1990 Dodge, How to determine failure of MAP sensor, IAC, TPS or vehicle speed sensor???

[leroyd92]

I replaced the coolant temp sensor today and drove it, same behavior as before. The stumble is getting to the point it's basically a fall flat on its face and die. Once it catches up it takes off and flys.

I'm going to park it and wait for the other sensors to come in. I feel this is the TPS but I'm going off of what I sold at O'Reilly for 7 years. Around here, the power boats get garage and the off-road / rock crawler toys come out.

I am discovering this truck is a time capsule from 1990. I can say with confidence ALMOST ALL OF THIS TRUCK IS UNTOUCHED. At least in the engine bay....

I never noticed the rear of the truck has a RV vent thing installed. It looks so good you'd almost think it's factory

 

[leroyd92]

I replaced the coolant temp sensor today and drove it, same behavior as before. The stumble is getting to the point it's basically a fall flat on its face and die. Once it catches up it takes off and flys.

I'm going to park it and wait for the other sensors to come in. I feel this is the TPS but I'm going off of what I sold at O'Reilly for 7 years. Around here, the power boats get garage and the off-road / rock crawler toys come out.

I am discovering this truck is a time capsule from 1990. I can say with confidence ALMOST ALL OF THIS TRUCK IS UNTOUCHED. At least in the engine bay....

I never noticed the rear of the truck has a RV vent thing installed. It looks so good you'd almost think it's factory

Upon further inspection, the vent in the roof was from Dodge

This just keeps getting better

 

[dishdude]

Upon further inspection, the vent in the roof was from Dodge

This just keeps getting better

I think we need some pictures of this beast!

 

[leroyd92]

Okay there's been a new development with absolutely no change in anything that I've done. The truck sat for over a week and I went to go start it and now that flat spot does it in park also. I can time after time push the gas pedal and make the engine stall out.

I then put the new map sensor in along with the new throttle position sensor, installing neither one, one at a time changed anything.

Is this sounding like the characteristic of anything in particular? I have not checked timing yet. Figure I'd say that now

 

[michaelluscher]

Okay there's been a new development with absolutely no change in anything that I've done. The truck sat for over a week and I went to go start it and now that flat spot does it in park also. I can time after time push the gas pedal and make the engine stall out.

I then put the new map sensor in along with the new throttle position sensor, installing neither one, one at a time changed anything.

Is this sounding like the characteristic of anything in particular? I have not checked timing yet. Figure I'd say that now

Start checking fuel pressure, Oxygen sensor activity, stuck purge valve?
Time for live data

How's ignition parts, cap/rotor and wires?

 

[leroyd92]

Long story short.

I put the original oe 35 year old FPR back on it and the stubble drastically went away. It's still there when the truck is very very cold but the behavior of the truck changed.

The stubble also became less when I made a 1/8" gasket for the EGR system and blocked it off, but the valve wasn't stuck.

My only issue now is as I'm coasting to a stop while the truck is cold, like, running for less than a minute cold, it will drop RPM so low it starts to die or will die.

I have a replacement IAC and hall sensor sitting on the table ready to go in if I can diagnose what it may be.

One thing I noticed, when you bump the throttle the scanner shows the timing retarding pretty rapidly.

I touched the throttle with a rod ( enough to tickle the RPM ~400 rpm) and watched the timing drop to like 7 or 4??????.


I've also put my foot on the throttle enough to maintain 7-800 rpm while the truck is still very cold, and it won't stall as I coast to a stop.

I drive like a grandpa, all of my driving is very part throttle and feather footed. My flat spot is right off of idle, and I can feel it getting smoother and smoother.

 

[leroyd92]

When the RPM drops low enough that I think it's going to stall, I can feel it catch up and try to correct itself. When it revs up it sounds like it revs to 8-900 rpm. So I know things are working, they are just lazy...

I was told to bypass the regulator and put an after market system in it that I can tune. I'm not that interested in that idea but I will if need be.


I am curious if it could be the hall sensor. The plug looks newish and I'm certain it's not OEM.

 

[mk378]

Get the CEL working so you can at least check for blink codes. Measure something, anything, to guide the diagnosis rather than firing the parts cannon blindly.

 

[leroyd92]

When the RPM drops low enough that I think it's going to stall, I can feel it catch up and try to correct itself. When it revs up it sounds like it revs to 8-900 rpm. So I know things are working, they are just lazy...

I was told to bypass the regulator and put an after market system in it that I can tune. I'm not that interested in that idea but I will if need be.


I am curious if it could be the hall sensor. The plug looks newish and I'm certain it's not OEM.

 

[leroyd92]

Are the blink codes more accurate than a mt2500 scanner?????!

 

[clinebarger]

Are the blink codes more accurate than a mt2500 scanner?????!

Snap-on software is pretty good with Domestic OBD1.....But DTC's are DTC's in the end no matter the retrieval process if done accurately.

Sensor/Scan Data can be fundamental to diagnostic's.....Doesn't necessarily have to be a MT2500, A first gen Solus/Pro or Modis would have the same software as a late MT2500 assuming it has Domestic Software to begin with.

 

[dishdude]

The ECMs weren't the greatest in these, they usually partially failed and would do odd things. Keep in mind how primitive the electronics were, and Chrysler liked to mount them in a plastic box under hood that air being sucked into the engine was pulled through. Not the greatest environment for a printed circuit board...plus you're dealing with 35 year old capacitors on the board.

 

[JHZR2]

The ECMs weren't the greatest in these, they usually partially failed and would do odd things. Keep in mind how primitive the electronics were, and Chrysler liked to mount them in a plastic box under hood that air being sucked into the engine was pulled through. Not the greatest environment for a printed circuit board...plus you're dealing with 35 year old capacitors on the board.

The capacitors to me would be the first suspect…

 

[mk378]

Yes bad capacitors in the ECU are common on old Hondas. Often it manifests as failure to start, but can also be various runnability issues.

 

[leroyd92]

Soooo, are you all suggesting that my issues can be better logged/tracked my the cel codes???

This is my first Dodge, if it was my 90 GM I wouldn't be asking these questions.

I assumed a scanner was the best way to log engine data. Tis why I acquired one.

If the cel flashes are better I'll figure out why it's not flashing. It doesn't light up when cranking over either.


I will tell you 1000% certain that putting the oe FPR back on the truck made it a completely different truck. The scanner now shows the exhaust switching from lean to rich, before it stayed on lean regardless of that I did with the throttle.

And within a day the truck stopped dieing as I coasted to a stop, I even backed the truck in last night and gave the motor ZERO time to idle before driving down the street, no stumble, no stall when I coasted to the end of my street

 

[wtd]

I'm not sure on that year of vehicle but no CEL with key on, engine off or initial cranking can indicate an ECM problem. I would definitely check to see if the light is burned out and if not, you will have to figure out why it's not coming on.

 

[leroyd92]

I'm not sure on that year of vehicle but no CEL with key on, engine off or initial cranking can indicate an ECM problem. I would definitely check to see if the light is burned out and if not, you will have to figure out why it's not coming on.

This is great to know.

I've been driving this truck daily for the last 3 days and it's been running perfect.

I'll acquire an ECM and keep all the spare parts i bought in the truck when I'm out hunting or in the desert. I purposely bought a " parts cannon" because it was going to go with the truck out in BFE anyways. But I want to know what does what when drivability issues show their ugly head