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Discussion Starter · #1 ·
I have a 1992 B2600i. It was given to me and I know about issues with the fuel pump on it's way out. And when I first got the truck there were no issues, other than having to pull over to vent the gas tank.
When the weather started to cool off but not yet cold, I could no longer just start up and go. It idled fine (1500rpm) but when I gave it gave gas it would drop down to 500rpm or so and when I took my foot off of the gas, it rose back up to 1500rpm.after maybe 15 min. or so, I could give it gas and it wouldn't die down and I could take off. I could put up with this for a while.
A while has passed and I can't take it, Now I have trouble even starting it. I have to pump the gas four or five times, take my foot off of the gas and then try to start it. It would catch but a no go. I then started to just leave the key fully turned to keep the starter running and it if caught, I'd let the key go. Id' still have to let it idle for quite awhile.
So, thinking it may be a thermal sensor, I'd let the truck idle for a bit and then turn it off. I was thinking that the engine compartment would be warming up the sensors. Sometimes it would work and sometimes, not! Since my truck is too old to do a OBD reading, I have to shoot in the dark.I took of the mass air flow and cleaned it with that spray stuff. Both ends were covered in a black like soot. I made sure it was clean and put it back on. My next thought was if the mass air sensor looks like this then what does the air filter look like? I went it to the auto parts store and had to order one. My next escapade will be to completely tear down the air intake system and fully clean it, including the throttle body and all. I have one question and I can't find the answer to it anywhere!!!!! Behind the air intake "pipe" there's a sensor coming out of it going into a black box and I found the name or "RESONANCE CHAMBER"!!!! Does anyone here have a clue what it's for and it's purpose????? Thank you for any and all help/suggestion that you may be able to contribute!!!!!
 

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Well, I am not mechanic but the resonance chamber on Subarus were on the air intake and did two things; they tuned the sound and did something to the air flow as it went into the intake. It is one of the items that Subaru guys who like to mess with their cars take off, it gives the engine a better sound according to them. It is also something that many people take off when they put in cold air intake systems.
 

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Discussion Starter · #3 ·
Well, I am not mechanic but the resonance chamber on Subarus were on the air intake and did two things; they tuned the sound and did something to the air flow as it went into the intake. It is one of the items that Subaru guys who like to mess with their cars take off, it gives the engine a better sound according to them. It is also something that many people take off when they put in cold air intake systems.
Thank you for that. I'll just proceed with my next step of cleaning the complete air intake system uncluding a new air filter. I've still a sneaking suspicion it's also one of the two temp sensors as well. It appears that after I let the truck warm up for about 10 minutes, turn it off and let set for maybe 5 minutes and restart that it cuts my "waiting time" about in half. really irritating at the moment. Will keep posting what I did and the results and hopefully something will click!!!!!
 

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If you knew about a fuel pump issue, I’d start there. I know it’s easier said than done but I’d check the volts and amps from the pump, if it’s getting weak yeah you could have those issues. Or check the output pressure of the pump. :)
 

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The smaller rubber hose that comes off of the air pipe, fits over an air jet or something similar to that......it is not a sensor.....it then goes into the valve cover, UNDER the resonance chamber. Any rubber hose or O-ring (at the resonator neck) that is part of the air intake tube into the throttle body, must fit tightly and not leaking any air. If anything along the air pipe fittings, from the Mass Airflow Sensor (MAF) to the Throttle Body, is leaking and pulling additional air into the throttle body downstream from the MAF, then the MAF is not reading the amount of air coming into the engine correctly. That small rubber hose is usually cracked, and hard as a rock, if it has never been replaced.......you can buy them new from your local Mazda dealer, or online from any Mazda Parts dealerships.

Another thing that could be causing your problems is the ECU. The original B2600i ECU's have been known to have two leaking capacitors (as they age) that will leak onto the circuit board and then etch the board and eventually create corrosion that will affect the injector circuits......creating idle & drivability issues. If you haven't looked at your ECU circuit board for corrosion, you may want to.

Another thing to check is the electrical harness plug that connects to the MAF.......the rubber cover will deteriorate and let moisture into the connector and cause some pin corrosion. There is a small hoop wire that retains the electrical connector, so you will need to pry it open to unplug the connector from the MAF.

Let us know what you discover.
 

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Discussion Starter · #6 ·
If you knew about a fuel pump issue, I’d start there. I know it’s easier said than done but I’d check the volts and amps from the pump, if it’s getting weak yeah you could have those issues. Or check the output pressure of the pump. :)
Yes, I was informed of this possible issue; however, #1 when I first got the truck it actually started and ran good other than occasionally having to pull over to vent the gas cap. #2 up until the weather changed and got colder in like Sept. or Oct. then my issues began. It would start and idle just fine but as soon as I applied any amount of pressure to the accelorator and held it like floored, the rpms would drop and would run really rough, spit and backfire and would "surge". The instant I took my foor off of the accelorator, it would recover and the rpms would go back up to 1500. Sometimes if I very lightly pressed the accelorator, it would go up to 2000 rpm but more when more pressure was applied, it would cough, spit, backfire and any other adjective you'd like to use. I now let it idle on cold start for about 5 min. I then play with the accelorator and turn it off for 2-3 minutes and turn it back on again. If the results were the same, I'd repeat. Sometimes, this will speed up the process as when I restart and rev the engine and the rpms jump up and continue to stay up, I'll be ok but it the rpms drop off irregardless of what I do, then I repeat the process. Once the engine warms up and I drive it, turn it off and restart before it totally cools down, I'm fine but if it gets too cold, I have to do the same process again. I'm thinking this is a seperate issue from the gas pump as I'm pretty sure the gas pump doesn't care about engine temp. I could be wrong!
 

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Discussion Starter · #7 ·
The smaller rubber hose that comes off of the air pipe, fits over an air jet or something similar to that......it is not a sensor.....it then goes into the valve cover, UNDER the resonance chamber. Any rubber hose or O-ring (at the resonator neck) that is part of the air intake tube into the throttle body, must fit tightly and not leaking any air. If anything along the air pipe fittings, from the Mass Airflow Sensor (MAF) to the Throttle Body, is leaking and pulling additional air into the throttle body downstream from the MAF, then the MAF is not reading the amount of air coming into the engine correctly. That small rubber hose is usually cracked, and hard as a rock, if it has never been replaced.......you can buy them new from your local Mazda dealer, or online from any Mazda Parts dealerships.

Another thing that could be causing your problems is the ECU. The original B2600i ECU's have been known to have two leaking capacitors (as they age) that will leak onto the circuit board and then etch the board and eventually create corrosion that will affect the injector circuits......creating idle & drivability issues. If you haven't looked at your ECU circuit board for corrosion, you may want to.

Another thing to check is the electrical harness plug that connects to the MAF.......the rubber cover will deteriorate and let moisture into the connector and cause some pin corrosion. There is a small hoop wire that retains the electrical connector, so you will need to pry it open to unplug the connector from the MAF.

Let us know what you discover.
I will check this out as well. Thank you so much. Not having a garage or a place to work on the truck long term, I have to be quick about it and show no tell tale signs. So anything I can do without attracting attention or making a mess.......I'm all for. Thanks again. More to follow.............
 

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Discussion Starter · #9 ·
The ECU is behind the passenger side kick panel......disconnect battery before you remove it to check the board. I think you are having ECU corrosion issues, myself.
As of this moment, I've replaced the air filter, cleaned out The MAF and sprayed some throttle body cleaner with the engine running and the air intake removed up to the throttle body. You can see pics of the airliners new and old side by side, nothing out of the ordinary there. Also a pic of the butterfly valve shut as it should be. What I did find interesting was the black line outside of the exhaust pipe after spraying the throttle body cleaner into the throttle body. J'll post pics in this order. Any more comments or suggestions are welcomed. Thank you
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Road surface Wood Automotive tire Rectangle Grey
 

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Discussion Starter · #10 ·
Sorry, working with my phone here isn't the best. It should read air filters.......I hate auto correct! The last pic is what I found on tge found after spraying that Throttle body cleaner directly into the carb while holding down on the throttle cable. It was really watery and looked like thick black soot. After doing this spraying a few times, I shut it down and put everything back together. NO DIFFERENCE!!!!! Should I do this longer or what???
 

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Like I've said a couple of times now......take a look at the ECU if you haven't yet. There are two original capacitors that will leak and etch the circuit board and then corrode the thin copper imprinting on the circuit board.......THIS IS A KNOWN ISSUE! It happens to all of the factory ECU's. Some last longer than others......some have already been "rebuilt"......some have been rebuilt well, some have not been!

Here is a factory ECU in pristine condition.....the RED & BLACK Capacitors are the culprits:

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Passive circuit component Circuit component Hardware programmer Electronic component Capacitor



Here is a factory ECU where the two red & black capacitors have leaked and repairs have been attempted......the BLACK capacitor has been replaced.....but this ECU still had issues:

Passive circuit component Circuit component Hardware programmer Electronic engineering Capacitor


Circuit component Electronic component Audio equipment Tableware Gas


Circuit component Passive circuit component Hardware programmer Electronic component Electronic engineering


Circuit component Passive circuit component Hardware programmer Gas Computer hardware
 

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Discussion Starter · #12 ·
Thank you. That's my next step. Don't qabtvyouvto think I'm disregarding or ignoring you! So, let's say I do find a faulty ECU, How do I resolve it and not get another faulty unit?
 

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If your computer shows no sign of corrosion, then it is not the computer that is giving you trouble......more than likely.

You can buy one through RockAuto.com also.....

 

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IF.......your ECU IS bad......you may want to check this company out......

 

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Discussion Starter · #19 ·
Hi "Axel". OK, so I've removed the ECU for inspection. For all intents and purposes, it appears brand new! I going to attempt to attach photos here. There were zero signs of corrosion or leakage whatsoever. You can see for yourself. Who knows maybe by disconnecting the battery and removing the ECU it may clear itself (wishful thinking). We'll see after I reinstall it and reconnect the battery. I'm still perplexed by the real rich rich exhaust and the thick black soot on the floor left when I do bait going. A residual from the throttle body cleaner? Anyway, it's always had a very rich odor in the exhaust with piss poor gas mileage. My best options are checking/replacing the two thermal sensors and a tune up. Like I said, when I first got the truck it started and ran fine but when thr weather changed, so did the truck
Passive circuit component Circuit component Computer data storage Hardware programmer Electronic instrument
Passive circuit component Circuit component Computer data storage Hardware programmer Electronic instrument
Circuit component Passive circuit component Hardware programmer Electronic engineering Electronic component

Passive circuit component Circuit component Hardware programmer Electronic engineering Electronic component

Passive circuit component Circuit component Hardware programmer Electronic engineering Audio equipment

Audio equipment Computer hardware Electronic device Machine Electronic engineering

Circuit component Passive circuit component Hardware programmer Electronic engineering Electronic component
 
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