Stalling 1998 Mazda B2500 - manual

[1998 b2500]

Hello everyone - hope all is well. I've got a problem with my B2500 (2.5 Ranger) and I need some kind help.

My truck is a 1998 Mazda B2500, 5 speed Manual transmission, with about 196,000 miles. Been running just fine until this stalling thing started.

Here's the symptoms: When cold, starts up, warms up. Once warm, it stalls. The engine will restart, may run for up to 30 seconds, then stalls. While driving, the truck will stall in gear, and feathering the gas pedal will get it to fire again for a bit. There is no "Check Engine Light."

My Actions:
1. Compression test is about 190 PSI on all 4 cylinders
2. cleaned MAF (no effect)
3. checked voltage and ohms at TPS (nothing out of ordinary)
4. Fuel pressure on the rail is 67 psi steady, running or key on
5. sprayed carb cleaner around engine while running and no effect on rpms
6. disconnected IAC when cold and the idle dropped about 500 rpm to 600ish rpm.
7. listened to fuel injectors - they are all clicking.

results:
no change! All above actions produced no changes. The truck still stalls with no load, barely runs without throttle play when warm. I'm stumped - and no check engine light!!!
Thanks in advance for your assistance.

 

[alwaysFlOoReD]

There may be pending codes. Did you look?
Also try a vacuum gauge, they can tell a lot about how an engine is running.

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[1998 b2500]

I have an OBDII scanner that talks to TORQUE (Android app). No fault codes. The app shows realtime data. When the engine is running, before it stalls, it shows about 21 on vaccum. The throttle is steady at 16.9. I'm guessing that the throttle is the signal from the TPS. Is this what you mean alwaysFlOoRed?

 

[PetroleumJunkie412]

Torque is mostly useless.

Welcome to TRS

 

[snoranger]

Is it stalling as it goes into closed loop?
If you have a way to see it (scanner, torque app, etc) watch and see if it stalls as soon as it switches out of open loop.
If you don’t have a way to see it, quick and dirty way... unplug the coolant temp sensor. (The one for the computer, not the one for the gauge.) That will keep it in open loop. If it still stalls, then we can start eliminating suspects.

 

[1998 b2500]

Is it stalling as it goes into closed loop?
If you have a way to see it (scanner, torque app, etc) watch and see if it stalls as soon as it switches out of open loop.
If you don’t have a way to see it, quick and dirty way... unplug the coolant temp sensor. (The one for the computer, not the one for the gauge.) That will keep it in open loop. If it still stalls, then we can start eliminating suspects.

Thanks!

I was not sure what to monitor in Torque -- so I unplugged the coolant temp sensors. There seem to be two - one on the cylinder head and one on the thermostat housing.

Started the truck and warmed it up. While it was warming, it stumbled/skipped a few times but kept running. After a few min, the rpm dropped to low idle, then it stalled. Truck would not restart until I plugged in the coolant sensors - then it would run a bit and stall right away.

I noticed this while watching gauges in Torque:
I was watching the vacuum guage on Torque. Usually it is steady at around 21 vacuum pretty smooth idle. Then, the gauge shows like 20 psi boost (I don't have a turbo!) and then 21 psi vacuum. When this happens, the engine is still running smooth. AFTER the vacuum gauge goes from vac -> boost -> vac, then it stalls.

 

[1998 b2500]

Torque is mostly useless.

Welcome to TRS

It is not easy to use. Torque gives me real time data, and I bought it thinking that since it had so many downloads, stars, etc.... it should be good, but definitely not intuitive. Do you have any apps that are more useful than Torque? Or easier to use?

 

[PetroleumJunkie412]

May want to check and see if forscan applies to your truck. If it does, get it and never look back ??

 

[alwaysFlOoReD]

Get a real vacuum gauge.

 

[1998 b2500]

May want to check and see if forscan applies to your truck. If it does, get it and never look back ??

Hey thanks PetroleumJunkie412. I gave it a try, found it on googleplay. For whatever reason, my S7 couldn't connect to my wifi OBDII tool . Oh well. What a weird stalling problem... my truck was running fine and all of a sudden... Talked to a good buddy of mine - he mentioned that I should look at the sensors with mechanical moving parts. In my motor, that would be the TPS and IAC. Gonna check it out and let you guys know...

 

[1998 b2500]

Get a real vacuum gauge.

Aww thanks! Do you think I should go for Snap-On? Or a cheapo from China on Amazon? I'm gonna check the moving sensors... let you guys know what I find... alwaysFlOoReD, do you have a recommended brand for Vacuum Guages? What port would you hook up to on the 2.5? Thanks for the tips!!! I really appreciate it.

 

[1998 b2500]

Thanks!

I was not sure what to monitor in Torque -- so I unplugged the coolant temp sensors. There seem to be two - one on the cylinder head and one on the thermostat housing.

Started the truck and warmed it up. While it was warming, it stumbled/skipped a few times but kept running. After a few min, the rpm dropped to low idle, then it stalled. Truck would not restart until I plugged in the coolant sensors - then it would run a bit and stall right away.

I noticed this while watching gauges in Torque:
I was watching the vacuum guage on Torque. Usually it is steady at around 21 vacuum pretty smooth idle. Then, the gauge shows like 20 psi boost (I don't have a turbo!) and then 21 psi vacuum. When this happens, the engine is still running smooth. AFTER the vacuum gauge goes from vac -> boost -> vac, then it stalls.

Alright, I decided I'd pull the IAC valve to check it out. Been looking on this forum for a couple of weeks and saw that people have some success after cleaning the IAC. So, I pulled it, it is a moving part with 196,xxx miles on it... not so bad looking, carbon on it. Cleaned it a bit, and was checking the movement... Seems like it just goes back and forth effortlessly. I applied a voltage to it and could feel the solenoid pulse but there is no movement.

I've been thinking... after pulling the coolant temp sensors, the truck suddenly stalled when warm. There were a few stumbles on the way. My TORQUE app shows throttle position at a steady 16.7%, no fluctuations. Since my truck has progressively stalled more over the testing process, I'm starting to think that a mechanical part -- like the infamous IAC might be it.

Gonna try swapping it. Will advise further.

 

[1998 b2500]

Alright, I decided I'd pull the IAC valve to check it out. Been looking on this forum for a couple of weeks and saw that people have some success after cleaning the IAC. So, I pulled it, it is a moving part with 196,xxx miles on it... not so bad looking, carbon on it. Cleaned it a bit, and was checking the movement... Seems like it just goes back and forth effortlessly. I applied a voltage to it and could feel the solenoid pulse but there is no movement.

I've been thinking... after pulling the coolant temp sensors, the truck suddenly stalled when warm. There were a few stumbles on the way. My TORQUE app shows throttle position at a steady 16.7%, no fluctuations. Since my truck has progressively stalled more over the testing process, I'm starting to think that a mechanical part -- like the infamous IAC might be it.

Gonna try swapping it. Will advise further.

OK... PROBLEM SOLVED. IT WAS THE IAC VALVE!!!!!!!!!!!!

It was the IAC Valve. I bought a new IAC from O'Reillys for about 50 bucks - and comparing my 196,xxx mile IAC to a new one I noticed the following:

1. Old IAC plunger has no resistance to movement back and forth;
2. New IAC plunger snaps back to a center position when pushed either way;
3. Old IAC will push closed or open and stay that way;
4. New IAC will snap back to center position;
5. Old IAC passed the "disconnect and see rpms drop" test;
6. New IAC was installed and just works! So I didn't bother with the "disconnect and see rpms drop" test.

So, bottom line, even though the IAC Valve passed the disconnect test, it was progressively failing. Looking back, it totally makes sense. After 196,xxx miles, an electrical solenoid may have seen its 15 minutes of fame...

Anyways, I just wanted to thank you guys for the ideas. I tried them and found the my solution.

Good luck guys (and gals)

and Happy Thanksgiving.

 

[1998 b2500]

OK... PROBLEM SOLVED. IT WAS THE IAC VALVE!!!!!!!!!!!!

It was the IAC Valve. I bought a new IAC from O'Reillys for about 50 bucks - and comparing my 196,xxx mile IAC to a new one I noticed the following:

1. Old IAC plunger has no resistance to movement back and forth;
2. New IAC plunger snaps back to a center position when pushed either way;
3. Old IAC will push closed or open and stay that way;
4. New IAC will snap back to center position;
5. Old IAC passed the "disconnect and see rpms drop" test;
6. New IAC was installed and just works! So I didn't bother with the "disconnect and see rpms drop" test.

So, bottom line, even though the IAC Valve passed the disconnect test, it was progressively failing. Looking back, it totally makes sense. After 196,xxx miles, an electrical solenoid may have seen its 15 minutes of fame...

Anyways, I just wanted to thank you guys for the ideas. I tried them and found the my solution.

Good luck guys (and gals)

and Happy Thanksgiving.

Oh yeah, one more thing... There were never any pending codes and never a check engine light with this problem. So weird! But I guess that is the signature of a failed IAC.

 

[alwaysFlOoReD]

Thanks for posting your fix.