[WhizzR]

Hi All -

I've been lurking in the forum for a couple of months now, soaking up the ambiance, and it's time to post.

I have a '91 B2600i 4x4 that I have an unnatural attachment to. Seriously, this truck and I have been through a lot together, and I don't mind putting a few bucks into it to keep it on it's wheels. Some work I've already done to it includes a complete R&R of the A/C system with an upgrade to R-134, a complete rebuild of the left-front 1/4 drive-train and suspension after a frozen bearing caused the entire outer axle and wheel to spin right off the truck (a great story if you want to hear it), a differential rebuild, and a complete brake replacement, including drums/rotors, and all pads/shoes.

A friend of mine who is retired mechanic recently did a complete engine overhaul for me. He pulled the engine, stripped it to the crank, and put in all new timing gears/chains/guides, new bearings, and a re-built head. Also in the mix were new plugs, wires, cap, etc.

After reassembling everything, he worked on and off for about a month trying to get the truck running properly. This past week he finally brought it back to me in frustration, saying he gave up. I've got nearly $900 in the engine repair (plus all of the other work I've done on this truck) and I really want to get it drivable. At this time, it will BARELY start when cold, and once hot, if shut off, it will not start at all. When it first starts, it sounds like it's only firing on a couple of cylinders, rather than on all four. This seems likely, as it is putting out thick black smoke, and there is a definite smell of unburned fuel. If you try to start it hot and fail, pulling the plugs reveals them to be soaked in gas. Drying them with compressed air sometimes helps to get it started again.

Other details you should know are that the reason for the engine rebuild was that I had a serious overheat with warped head. The truck sat in my driveway for quite a while before I went ahead with the rebuild -- probably long enough for the gas to go REALLY bad. My mechanic drained and cleaned the tank, and ran a large amount of highly-concentrated fuel system cleaner through it. Among other new parts that have been installed are a new O2 sensor, and a new fuel pump.

The Check Engine light is currently on, but I couldn't get the ECU to flash any codes. I had picked up a used ECU of unknown condition on eBay really cheap, but when I pulled my pax side kick panel, I was shocked to find an ECU there that says it is made by Mitsubishi, and it was refurbed in 1999 by a 3rd party (NOT AvPro). The ECU that's installed doesn't look anything like the one that I got off eBay. It's far larger, and seems to have a different wiring bundle interface. I had no idea the ECU had ever been changed out. The engine appears to be the original G6 engine that the truck came with.

So I'm looking for some ideas. I can post pictures of the ECU that I found in the truck if that will help at all. I also have a new set of fuel injectors that I don't know for sure if I need. I've been reluctant to install them, because if they don't fix the problem, I can't return them once they're used.

Sorry so long, but this has been a long saga. Any help would be VERY MUCH appreciated!!!

-jeff in Florida

 

[Tyranitar]

Ok, it does seem that there is an issue with the injector drivers. Being refurbished by a company other than AVPro is significant, because AVPro is the only company that removes the contaminated humiseal coating in addition to repairing the damaged components. If the contaminated coating is not removed, failure is guaranteed. The computer used in these Mazdas was manufactured by Mitsubishi Electronics, which is a different department than Mitsubishi Motors. I would be interested in seeing both computers and how they are different. I would also recommend opening the ECU that is in the truck right now and looking for the same corrosion signs that an original failed unit would have.

 

[WhizzR]

Thanks for the reply!

As soon as I can snap a couple of pix, I'll post them here.

One other thing I forgot to mention yesterday (as if my original message wasn't already long enough) is that the ECU that I just purchased from eBay is from a 2WD truck, where my truck is a 4x4. Is there supposed to be a significant difference in these ECUs? The two I have a nothing alike. I'm thinking maybe that the 2WD one is from a truck without EFI?

Regards!

-jeff in Florida

 

[WhizzR]

Ok, it does seem that there is an issue with the injector drivers. Being refurbished by a company other than AVPro is significant, because AVPro is the only company that removes the contaminated humiseal coating in addition to repairing the damaged components. If the contaminated coating is not removed, failure is guaranteed. The computer used in these Mazdas was manufactured by Mitsubishi Electronics, which is a different department than Mitsubishi Motors. I would be interested in seeing both computers and how they are different. I would also recommend opening the ECU that is in the truck right now and looking for the same corrosion signs that an original failed unit would have.[/b]

Hi Ty (and everyone else) -

Well, since my last post, I've sent off my truck's fuel injectors for re-build (which didn't help anything) and I pulled the ECU and sent it off to be re-built by AVPRO (which didn't help either), and I've put in a new battery, because the old one kakked on me, probably from endless cranking.

To re-iterate: I've done a complete rebuild on this engine, and I can get it started (barely) when it's stone cold, but it runs badly, and once shut off, if it's even a LITTLE warm, it won't restart. The CHECK ENGINE light is on, but I can't get the ECU to flash any codes. Most recently, I verified that the cap and rotor were good, and that the plug wires are on in the correct order (gotta check out the BASICS sometimes).

Ideas! I need ideas!!! This truck is killing me!

-jeff in Florida

 

[Tyranitar]

Ok, the MAF sensor if faulty or dirty, or disconnected, can cause a non-running condition. Have you checked the fuel pressure when this non-running condition occurs? Is it possible that a wire harness has been damaged during the engine rebuild? I would not rule out the possibility of a faulty PIP as well. I wish I knew which wire to probe with an LED strobe light or oscilloscope, but a bad PIP could very well behave differently depending on temperature. Since PIP also signals to fire the injectors, this could cause the problem.

 

[WhizzR]

Ok, the MAF sensor if faulty or dirty, or disconnected, can cause a non-running condition. Have you checked the fuel pressure when this non-running condition occurs? Is it possible that a wire harness has been damaged during the engine rebuild? I would not rule out the possibility of a faulty PIP as well. I wish I knew which wire to probe with an LED strobe light or oscilloscope, but a bad PIP could very well behave differently depending on temperature. Since PIP also signals to fire the injectors, this could cause the problem.[/b]

Sorry, but I'm not up on all the acronyms -- PIP? I poked around the internet, and the closest I could come is "Profile Ignition Pickup". Not sure where this is, or how to test it. Is this what you meant?

To answer your question, no, I have not checked the fuel pressure. I can tell you that part of the refurb on this truck has been to R&R the pump and screen. My mechanic friend told me that the truck IS getting fuel - now, whether the pressure is within tolerance is another story. I don't even have the tools to check the pressure, but I imagine I could either rig up something, or borrow it.

What's the best way to clean the MAFS? I was going to pick up some spray cleaner at the auto parts store, but I hear that the MAFS can be easily damaged if mistreated. They're expensive to replace, so I'm a little reluctant to go at it without some consultation.

Yes, it is possible that a harness was damaged. Heck, for that matter, ANYTHING is possible with this engine re-build. I did not actively take part in the actual R&R - I was the "money man" who supplied parts and money on demand. *SIGH* I have well over $1200 invested in this engine right now, and nothing to show for it. It MUST be mighty close to being operational - after all, I've replaced almost everything replacable! About all that's left is the distributor. I tested the spark last night, both at the coil wire, and at the end of one of the plug wires, and it was strong enough to jump a gap over 1/2" wide, so I'm thinking that the ignition is okay (not necessarily including the timing, which I think may have been set without grounding the test connector). Last night I opened the air cleaner to check the filter. It was dirty, but not plugged. Nevertheless, I left it out temporarily, and after that the engine wouldn't even so much as PUTT even once. Just endless cranking, cranking, cranking. I pulled one of the plugs, and it was wet with gas (but not SOAKED). I never did get it to start again before the mosquitoes drove me indoors for the evening.

I went about 1/3 of the way through this forum last night, pulling every thread that related to engine starting, running and quitting, hard starting when warm, etc. I'm consolidating and condensing the possible causes and fixes. When I'm through, I'll re-post it, and hopefully we can get it into a FAQ, because these problems seem like a common occurances as these trucks age.

Meanwhile, I've seen at least 4 different descriptions of how to pull codes out of the ECU. The one on AVPRO's website seems to be inaccurate (the test connector is not where they say it should be). Ty, after reading all your posts, I value your expertise perhaps most of all, so could YOU please post a set of instructions on how to pull codes? Please don't just say stuff like "Ground the test connector" because the vast majority of people who read these (myself included) do not know where the test connector is located.

Thanks! And thanks for your willingness to share your knowlege!

-jeff in Florida

 

[Tyranitar]

The PIP is the signal inside the distributor that indicates camshaft position. The ECU uses it for ignition and injector timing. If it is weak or erratic, it can cause problems. The MAF sensor should be cleaned with either electrical parts cleaner, or MAF sensor cleaner. Since you mentioned it would not start at all without the filter, this may suggest an issue with that paticular sensor. Try unplugging its electrical connector and see if anything changes. I'm not sure what will happen if you do this, but I know on several Ford designs, that unplugging the MAF causes the computer to try to operate without it, often with much greater success than if it is left connected. You obviously should run very long like this, but it does help isolate the problems.

Now on the subject of the diagnostic connector, where is yours located?

 

[WhizzR]

The PIP is the signal inside the distributor that indicates camshaft position. The ECU uses it for ignition and injector timing. If it is weak or erratic, it can cause problems. The MAF sensor should be cleaned with either electrical parts cleaner, or MAF sensor cleaner. Since you mentioned it would not start at all without the filter, this may suggest an issue with that paticular sensor. Try unplugging its electrical connector and see if anything changes. I'm not sure what will happen if you do this, but I know on several Ford designs, that unplugging the MAF causes the computer to try to operate without it, often with much greater success than if it is left connected. You obviously should run very long like this, but it does help isolate the problems.

Now on the subject of the diagnostic connector, where is yours located?[/b]

I guess I forgot to mention in my last post that also last night, I tried unplugging the MAFS - no difference. However, as I sit here thinking about it, that's about the point when it stopped even giving me a "PUTT" once in a while. When I quit, it was free-cranking with NO detonation activity that I could detect.

What I believe is the diagnostic connector is up by the windshield wiper motor. There are two connectors there - both are 6-wire molex housings, but one is white and has 5 wires, and the other is green and only has three. The white one is the one that has always been plugged in there, but I believe I've had the truck running with either, or even NEITHER of them plugged in. At some point in this truck's illustrious past, someone removed about an inch of insulation from one of the wires on the white connector, and spliced in a wire to an electric radiator fan (the original clutch fan has been removed). In all my testing, I've been keeping the fan power wire disconnected, to ensure it's not having any unexpected effect on the system - once I get everything working, I hope to put in a new thermostat to control this fan. Bear in mind, the truck used to run just fine with this wire connected directly to the wire leading into the white molex -- BEFORE I had the engine rebuilt.

Now, up near the above-mentioned green molex connector, coming out of the same wiring bundle (I believe) is another, smaller green molex, which I think has only a single wire. This is what I think is the connector that needs to be grounded to flash ECU codes, but as I've previously indicated, I've never gotten my ECU to flash ANYTHING.

That begs a question - if your ECU has no current codes, is there a "No Codes" signal?

Sorry for all the "I thinks" and "I believes" - but I'm at work, and therefore can't go look at the truck to verify. When I get home, if it turns out something is different, I'll let you know.

-jeff in Florida

Update: Just got in from working on this beast. Brought home some MAFS cleaner - no change. I also used contact cleaner on several of the main connectors, to ensure they're clean. Again, no change.

I double-checked the diagnostic connector configuration. All of above-mentioned connectors emerge from the same wire bundle up near the wiper motor. What I said was correct: There is a white one with 5 wires, a green one with 3 wires, and a small green one with 1 wire. I tested this with a meter, and it has 12 volts on it. I grounded it, and turned on the key, but my CEL stayed lit solid. There is also a connector with two wires. Of all these connectors, only the white one is connected to anything.

As of now, I STILL cannot even get so much as a single "PUTT" out of this newly rebuilt engine.

I pulled off the fuel line as it exits the filter to make sure fuel is getting where it's supposed to be. Yes, there's fuel there, but I'm not sure the pressure is as high as it should be. I'm going to rig up a pressure test tomorrow, and see if I can find out exactly what the pressure is. I'm also going to get a new filter just because it's one consumable that I haven't replaced yet.

SCADS! This is frustrating! If I didn't like the truck so much (and if I didn't have so much $$$ wrapped up in this repair) I might just junk the darn thing!

 

[Tyranitar]

Yes, AVPROs instructions are incorrect as far as the location of the wire is concerned, however, the procedure should work. However, in mine, it does not get me any codes either. I'm not sure if there is something more to it or what? I will do some more checking to see what if anything more is required to pull codes.

 

[Tyranitar]

Ok, did a bit more checking, including a call to the Mazda dealer. Didn't find out much of anything. I would check along the entire wire harness to see if there are any connectors unhooked, or wires that may have been damaged. I talked to the guys at AVPRO, and they said that it is possible the computer may still have an issue, but that it is unlikely, as they test drive each computer in their 2.6L MPV. Which by the way, that is why the code instructions are wrong. The diagnostic connector is on the driver side on the MPV, but on the passenger side on the B2600i. According to the Mazda Dealer, grounding that connector may flash the codes, but that it does not always work. Is the CEL on with the ignition off, or is it on when you get the engine running? It is normal for it to be on when the engine is not running, it is only important if the engine is running and the light comes on. So far everything here seems to point to a faulty MAF sensor. On my Aerostar, my MAF sensor went out while I was driving. When it went, the engine had no power and began misfiring, like it was shutting down ignition. It then killed when I tried to let it idle. It would not restart till it cooled down, and then it ran very poorly. These symptoms seem to closely mimic the ones you describe. I know they are different vehicles, but the same principles may apply here. My van was easy to diagnose however, since it was easy to pull the codes on. It actually had 4 codes related to MAF function.

It is entirely possible that to consistently pull codes, and more elaborated reader may be required. I will see what I can come up with.

 

[WhizzR]

Ok, did a bit more checking, including a call to the Mazda dealer. Didn't find out much of anything. I would check along the entire wire harness to see if there are any connectors unhooked, or wires that may have been damaged. I talked to the guys at AVPRO, and they said that it is possible the computer may still have an issue, but that it is unlikely, as they test drive each computer in their 2.6L MPV. Which by the way, that is why the code instructions are wrong. The diagnostic connector is on the driver side on the MPV, but on the passenger side on the B2600i. According to the Mazda Dealer, grounding that connector may flash the codes, but that it does not always work. Is the CEL on with the ignition off, or is it on when you get the engine running? It is normal for it to be on when the engine is not running, it is only important if the engine is running and the light comes on. So far everything here seems to point to a faulty MAF sensor. On my Aerostar, my MAF sensor went out while I was driving. When it went, the engine had no power and began misfiring, like it was shutting down ignition. It then killed when I tried to let it idle. It would not restart till it cooled down, and then it ran very poorly. These symptoms seem to closely mimic the ones you describe. I know they are different vehicles, but the same principles may apply here. My van was easy to diagnose however, since it was easy to pull the codes on. It actually had 4 codes related to MAF function.

It is entirely possible that to consistently pull codes, and more elaborated reader may be required. I will see what I can come up with.[/b]

As usual, thanks for the reply. I'm fascinated that you're not able to pull codes either. Is that because your ECU doesn't contain any tripped codes? Did you try to do anything that would cause a fault, like pull the MAFS connector? If there is ANYBODY ELSE reading this that has successfully pulled codes on a 91 B2600i, please jump on in and give your 2 cents worth!

I will check into the cost of a new MAFS, but I'm afraid it's going to be pricey, and I'm getting reluctant to keep throwing expensive parts into this thing with no results. The injectors and ECU alone were over $350 between them, and in retrospect, I'm not sure I needed either one.

I'm a little disappointed in the response the Mazda dealership gave you. "Grounding the connector may flash the codes..." May??? "...but that does not always work..." Well that's great. What good is the connector if you can't rely on it to pull the codes? How do they do it when they can't use the diagnostic port? I remember reading somewhere (possibly a Chilton's manual) about a method to use an analog multimeter to pull codes by counting the number of "sweeps" of the needle when the meter is connected up to a particular wire. I can't find those instructions at the moment, but the last time I tried them, either they didn't work, or I had the wrong port.

To answer your question, when the key is turned on the CEL is illuminated all the time - whether the engine is running or not. I expect it to be on when the ignition is on but the engine hasn't been started, but it remains lit even after it starts. Not that I've seen it start lately - it's been two days since I could get the engine to do ANYTHING other than turn over.

If I'm able to successfully test the fuel pressure tonight, I'll post my results for you. It should be around 7:00 PM Central time.

-jeff in Florida

Update: Just got in from working on the lump, er, truck. Today I bought it a new fuel filter, and some parts to rig up a pressure tester. The pressure on the engine-side of the filter was over 40 PSI, and jumped to 60 PSI when I stopped cranking. So, that looked good. Unfortunately, I still can't get any activity out of the engine.

I pulled the #1 plug, (it was wet with fuel) and did a pressure test, and as expected, got really good results. It held over 160 PSI rock solid for 2 minutes. I once again poked around looking for loose connectors, and damaged wires, but found nothing. I tried cranking it over both with and without the MAFS connected. I tested the spark both at the coil wire, and the end of the plug wires. Everything looks fine. I just won't freakin' kick over. After some serious cranking I sniffed near the exhaust, and I could smell gas. So between that, and the plug being wet I'm assuming that it's getting fuel into the cylinders.


_{Anyone wanna buy a truck?} :thumbsdown:

 

[Midnight Mechanic]

I recently had my b2200 redone by the pro's and they had the timing off a tooth. Take a look just for kicks if everything is lined up. That one stumped me for months.

 

[WhizzR]

I recently had my b2200 redone by the pro's and they had the timing off a tooth. Take a look just for kicks if everything is lined up. That one stumped me for months.[/b]

Up until I pulled the MAFS the other day, I could get it to start when stone cold - just not when it was warm. When it was running, it ran pretty badly, and wouldn't idle very well. For the last several days I can't get ANYTHING out of the engine...

 

[Tyranitar]

Well, if the timing is off enough, and I'm assuming you've set it correctly, it might cause an issue. I am thinking this is a MAF issue, but by the same token, that is an awfully expensive part to experiment with. Try calling a few junk yards, and see if someone might per change have a 1989 -1993 B2600i in the yard. If they do, and it still has the MAF in it, then you can try swapping a used one and see what happens. The problem is, these trucks are not very common. A 4 cylinder MPV will also do nicely. Those are not very common, since most MPV buyers opted for the V6.
With mine, it just stopped running right one day and after a lot of frustration, I found a post on this very forum referring to AV Pro. I checked it out, send the computer in, and when it came back, I plugged it in. The truck started up rough, but once it got going and cleared its throat, it never gave me the same sort of trouble again. But I have had a couple run ins with the MAf sensor, and when it gets dirty, the truck starts stumbling and running rough. I have tried to force a code, but the thing is, the only major sensor I can mess with that does anything when I unhook it is the MAF, and then it doesn't want to run at all. Unhooking the O2 does nothing, though I'm sure the fuel economy drops.

 

[smuryof]

Whizz,

Where are you located? Anywhere near Utah? I have a storage shed with quite a few extra parts. I think I may have a MAF sensor.

Keep in mind that plugs repeatedly soaked in gas (as you are describing) can have ruined ceramic and end up grounding themselves out. Maybe during the course of all this testing, your plugs were ruined in this way and quit firing altogether. You could pull one and hold it against the engine block & check for your blue spark.

-Jim ('91 B2600i @ 240,000 miles)

 

[WhizzR]

Whizz,

Where are you located? Anywhere near Utah? I have a storage shed with quite a few extra parts. I think I may have a MAF sensor.

Keep in mind that plugs repeatedly soaked in gas (as you are describing) can have ruined ceramic and end up grounding themselves out. Maybe during the course of all this testing, your plugs were ruined in this way and quit firing altogether. You could pull one and hold it against the engine block & check for your blue spark.

-Jim ('91 B2600i @ 240,000 miles)[/b]

Hi Jim -

No, sorry - nowhere near Utah. I'm in the Florida Panhandle, not too far from Pensacola. However, if you have a MAF sensor that you'd like to give away or sell, I'd be pretty interested. Please let me know.

Latest saga: Today I pulled all the plugs, recleaned and gapped them, and spun the engine over to a few degrees before TDC to be sure it is at least sparking out the right tower in the cap. As is becoming a frustrating norm, everything checked out good, but I couldn't get ANYTHING out of the engine. Now, after a week of cranking, the battery is finally starting to die, so I'm going to pick up a charger this weekend.

-jeff in Florida

 

[smuryof]

Let's go back to basics. Fuel and spark. I leave out compression, because if compression were an issue you'd at least get something.

I advise picking up a set of 4 of the cheapest plugs you can find and trying with those to see if you get anything. Try holding each plug, wire connected, against a ground (bolt head or something) to ensure you get a solid blue spark.

If you use brand new spark plugs, get solid blue sparks, the engine is not firing, and your plugs are getting soaked in gas, you can solidly conclude that you are getting way too much gas in the cylinders. But again, if your plugs are already ruined, you'll never know when you've got it fixed because they just won't fire.

If your truck does not fire within the first two seconds of cranking, it isn't going to - try not to crank more than 3 or 4 seconds at a time, is my advice.

So, get new plugs, crank for 2 secs, if the problem is the same, pull plug 1 and see if it is getting blue spark on cranking. If so, unplug the throttle position sensor to see if anything happens. Doublecheck the air intake from the air filter to the throttle body to make sure a hamster didn't climb in there and die, or something.

If none of that helps, yea you can swap out the MAF and/or your injectors, but I would doublecheck those things first.

 

[WhizzR]

Let's go back to basics. Fuel and spark. I leave out compression, because if compression were an issue you'd at least get something.

I advise picking up a set of 4 of the cheapest plugs you can find and trying with those to see if you get anything. Try holding each plug, wire connected, against a ground (bolt head or something) to ensure you get a solid blue spark.

If you use brand new spark plugs, get solid blue sparks, the engine is not firing, and your plugs are getting soaked in gas, you can solidly conclude that you are getting way too much gas in the cylinders. But again, if your plugs are already ruined, you'll never know when you've got it fixed because they just won't fire.

If your truck does not fire within the first two seconds of cranking, it isn't going to - try not to crank more than 3 or 4 seconds at a time, is my advice.

So, get new plugs, crank for 2 secs, if the problem is the same, pull plug 1 and see if it is getting blue spark on cranking. If so, unplug the throttle position sensor to see if anything happens. Doublecheck the air intake from the air filter to the throttle body to make sure a hamster didn't climb in there and die, or something.

If none of that helps, yea you can swap out the MAF and/or your injectors, but I would doublecheck those things first.[/b]

The "get back to the basics" is a good idea. So good, in fact, that I thought of it the other day. That's when I stopped messing with the MAFS, and the wiring, etc, and started verifying the three cornerstones of a running engine: spark, compression, and fuel. I've tested each of these to my satisfaction, but I only really tried one plug on the end of it's wire. Reading your e-mail reminded me that I had picked up a new set of plugs off of eBay a month ago or so. If I have the time tomorrow, I'll pull the wires, ground the plugs, and have my wife crank to verify the spark. I'll let you know the results...

Thanks for the suggestions.

-jeff in Florida

 

[smuryof]

... If I have the time tomorrow, I'll pull the wires, ground the plugs, and have my wife crank to verify the spark. I'll let you know the results...[/b]

Forgot to mention, make sure you are holding it firmly against grounded metal, and wear rubber gloves if you can. It sucks to get jolted by the 10,000 volts or so that the coil generates.

Looking forward to hearing the results...

 

[WhizzR]

Forgot to mention, make sure you are holding it firmly against grounded metal, and wear rubber gloves if you can. It sucks to get jolted by the 10,000 volts or so that the coil generates.

Looking forward to hearing the results...[/b]

I do appreciate all the warnings and you trying to look out for my best interest, but I should tell you that I've been working on engines since the late 1970's, and I was a mechanic in the Air Force from 1982-1985. :thumbsup:

That's the reason this whole business with this Mazda truck is so darn frustrating. :grr: NOTHING that I can draw from my past experiences has had any effect in getting this thing running.

So the cautions, while appreciated, are unnecessary - - at least for me. Perhaps someone else reading these posts might be helped though. BTW - typical coils generate at least 5x the voltage you mentioned above. Some go as high as 100,000 volts. (w00t) SHOCKING!

-jeff in Florida