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85 New Yorker 2.2 T1, multiple red 1991 Spirit R/T's, lots of bits and pieces
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Discussion Starter · #1 ·
I've got a 91 Spirit R/T that has a somewhat common problem. Sometimes it's great, sometimes it lacks throttle response sometimes. Here is one very specific symptom: Closing throttle (such as while driving mildly around town and letting off the throttle before shifting) causes a sudden surge forward for just a moment. Another symptom is that it just doesn't have much power, unless the throttle is feathered just right.

From my reading, it appears to be a common problem from having a poor electrical connection to the TPS or a bad TPS itself.

All three of my red 1991 Dodge Spirit R/T's had this same problem. (Of those, one was stripped and another was converted to 8v.) I've tried a handful of TPS's, including a new one, a couple that work perfectly in 8v, and various ones from other SBEC cars. Each behaves differently! For example, the one installed now has a strong idle oscillation and an occasional backfire. The previous one would bog down at stops. I've spliced in a new connector. I even used a drill bit to clean all of the connectors. I've replaced the SBEC-II. (I have a second stock one as well as a FWD Stage 1 calibration.) I've had the same problem on three wiring harnesses, and I also did my best to ensure good contact there. I double-checked all of the vacuum lines.

When testing the TPS, rising up from 2v to about 2.6v and then going back down causes a jump on ALL TPS's! I also cleaned and reattached all ground straps.

I'm still confident that it's related the TPS or the TPS wiring somehow, because of exactly how it behaves. I have one Chrysler marked TPS, one no-name TPS, and four Holley TPS's, all of which test bad. I'm out of stuff to change!
 

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I've got a 91 Spirit R/T that has a somewhat common problem. Sometimes it's great, sometimes it lacks throttle response sometimes. Here is one very specific symptom: Closing throttle (such as while driving mildly around town and letting off the throttle before shifting) causes a sudden surge forward for just a moment. Another symptom is that it just doesn't have much power, unless the throttle is feathered just right.

From my reading, it appears to be a common problem from having a poor electrical connection to the TPS or a bad TPS itself.

All three of my red 1991 Dodge Spirit R/T's had this same problem. (Of those, one was stripped and another was converted to 8v.) I've tried a handful of TPS's, including a new one, a couple that work perfectly in 8v, and various ones from other SBEC cars. Each behaves differently! For example, the one installed now has a strong idle oscillation and an occasional backfire. The previous one would bog down at stops. I've spliced in a new connector. I even used a drill bit to clean all of the connectors. I've replaced the SBEC-II. (I have a second stock one as well as a FWD Stage 1 calibration.) I've had the same problem on three wiring harnesses, and I also did my best to ensure good contact there. I double-checked all of the vacuum lines.

When testing the TPS, rising up from 2v to about 2.6v and then going back down causes a jump on ALL TPS's! I also cleaned and reattached all ground straps.

I'm still confident that it's related the TPS or the TPS wiring somehow, because of exactly how it behaves. I have one Chrysler marked TPS, one no-name TPS, and four Holley TPS's, all of which test bad. I'm out of stuff to change!
Sounds like a grounding issue.
 

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85 New Yorker 2.2 T1, multiple red 1991 Spirit R/T's, lots of bits and pieces
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Discussion Starter · #3 ·
Sounds like a grounding issue.
I thought the same thing. I've sanded and reattached all of the ground straps and also manually grounded the TPS pigtail. Jackson Simler suggests checking the speed sensor, which I'll swap out today and see.
 

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Discussion Starter · #4 ·
Well, that raised more questions than it answered... The speedo was working fine with the old speed sensor, but when I pulled it out, it was obliterated, and the electrical connector was rust-tastic! The new speed sensor popped right in (and I stripped out the bolt threads). It didn't get rid of the buck/surge behavior of the throttle when closed, but it seems to have restored consistent acceleration during boosty pulls.

I think I need to just keep buying TPS's until I find one that the car likes. shrug
 

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85 New Yorker 2.2 T1, multiple red 1991 Spirit R/T's, lots of bits and pieces
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Discussion Starter · #5 ·
I hate this car! :-D I got another TPS, and it bucks but also stalls and the idle hunts around randomly. It tests bad in the car and on the bench. (Does nobody make a good TPS for SBEC anymore?)

While searching for a sensor that works, I continued looking down other possible routes. I found a mystery vacuum line, which I plugged. I also read that some people have this same idle surging/bucking problem when the PCV valve grommet leaks. Well guess what....huge leak! I replaced it, and it's super tight, and the problem is still there.
 

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I hate this car! :-D I got another TPS, and it bucks but also stalls and the idle hunts around randomly. It tests bad in the car and on the bench. (Does nobody make a good TPS for SBEC anymore?)

While searching for a sensor that works, I continued looking down other possible routes. I found a mystery vacuum line, which I plugged. I also read that some people have this same idle surging/bucking problem when the PCV valve grommet leaks. Well guess what....huge leak! I replaced it, and it's super tight, and the problem is still there.
Was it new? I've never had a tps issue on over 50 of these cars?

My Tbi car had a similar issue and it was the idle being set too low, bad plugs and my intake coolant bypass.

Try bumping the idle stop as high as u can without rpm rise. (The IAC will back off automatically)

Also try blocking all vac stuff besides pcv,booster and map sensor to eliminate any possible vac leak areas..
 

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Discussion Starter · #7 ·
The TPS I just tested was used but had less than 500 miles on it. (I bought it to use on the Spirit that shattered a head.) To be clear, even the "bad" ones work perfectly fine in the 8v. They're imperfect, but the 8v cars don't seem to care. My test method is either on-car or with a Korad power supply. They're showing lower than expected voltage on closed throttle plate and inconsistent readings across the throttle range.

Bumping the idle up sounds like a good idea. I found that I can avoid the problem if I never fully close the throttle... I also like the idea of blocking all of the "unnecessary" vacuum lines. I'll try that first, then the idle next. I have a new TPS coming from a brand I haven't tried yet, so I'll give that a go.

Part of me says, "This can't possibly still be a TPS problem, because you've tried so many sensors and plugs." Another part of me says, "It's gotta be TPS related, since it drives so very differently with each one."
 

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The TPS I just tested was used but had less than 500 miles on it. (I bought it to use on the Spirit that shattered a head.) To be clear, even the "bad" ones work perfectly fine in the 8v. They're imperfect, but the 8v cars don't seem to care. My test method is either on-car or with a Korad power supply. They're showing lower than expected voltage on closed throttle plate and inconsistent readings across the throttle range.

Bumping the idle up sounds like a good idea. I found that I can avoid the problem if I never fully close the throttle... I also like the idea of blocking all of the "unnecessary" vacuum lines. I'll try that first, then the idle next. I have a new TPS coming from a brand I haven't tried yet, so I'll give that a go.

Part of me says, "This can't possibly still be a TPS problem, because you've tried so many sensors and plugs." Another part of me says, "It's gotta be TPS related, since it drives so very differently with each one."
I was about to donate the Tbi car to the local gun range for their machine gun shoot. It was bucking,stalling basically undrivable in closed loop. I tried taping and gluing the pcv neck for any leaks and it did nothing.

In the end swapping to the used NGK plugs from the cracked head, reconnecting the intake heater hoses and the idle adjustment fixed it.

Now it's driven daily. Minor issues are 1 second idle drop when aftermarket fan kicks on (maybe too many amps), cooling fan comes on early or temp Guage isn't going past 1/4 and it felt random rough idle but swapped in a used cap/wires got it running smoother.

Maybe try different brand plugs and a tighter gap?
Also add extra grounds. I've been doing this for years and it cleared up a ton of electrical gremlins.

Run a ground from the battery Negative to the strut tower then the strut tower to the engine block. My 92 Sentra,05 Altima, and the $200 junkyard 89 Honda Prelude here all had stalling/running issues and this fixed it.

Motor vehicle Automotive air manifold Hood Car Vehicle
 

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Discussion Starter · #9 ·
I was thinking of adding a couple grounds in what I think are key locations. At least that's something that wouldn't hurt regardless.

And your story about how the car almost met its demise reminds me of a conversation I had with a coworker.

Me: "I'm gonna head up to the pistol range later and shoot the Taurus."
Him: "You still have that car??"
 

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1992 dodge shadow es turbo
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Have you looked at maybe the map sensor, or do you have access to a scan tool to watch live data on the sensors? If not you could temp wire in a volt meter to the signal wire and watch live voltage when it is acting up.
 

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Discussion Starter · #11 ·
I did replace the MAP and boost sensor, as well as the hose going to it, but I didn't run a live data test. That would have been a good idea. Even if the problem turns out to be a vacuum leak, that will help me determine that. I'll start with stripping down the vacuum system, then adding grounds, then see what makes the most sense next. Lots of possibilities.
 

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UGH, MAP sensors. Guys over at TM forums actually bench test the sensors with air compressor. Put a regulator on, and carefully test the full range of the MAP.
 

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Discussion Starter · #13 ·
Updates....

I removed everything but brakes, HVAC, wastegate, MAP/Bar sensor, PCV (which I sealed up tight), and fuel pressure regulator. In other words, I removed cruise control and a bunch of emissions stuff. It still had the buck/surge, but this time it backfired. Wheee!

I put those back and raised the idle by putting a strap around the throttle stop. Idle hunted a lot, mostly around 2,250, but the problem persisted.

I put the MAP/Boost sensor from the Shadow in. It ran rough for about a quarter mile, then died and left me stranded. No codes, just acted like it was out of fuel. So, I put the old one back in, and it drove like an entirely different car! It was super responsive. I couldn't believe how fast it built up boost and how strong it pulled throughout the RPM range! I drove for about 20 minutes with no problem! I took it home, and literally two blocks from my house it started the buck/surge thing again and now it doesn't drive right anymore.

I'm gonna guess it's somehow MAP/Bar related. It makes sense. (Well, a bad TPS made sense. A vacuum leak around the PCV valve made sense. The shattered VSS made sense....) If I give it just a little gas, it just starts to build boost, and then I let off of the throttle and it backs off to vacuum, so if it's not accurately reading that little range right between boost and vac, then it has a lot of reason to be angry. They're new hoses. The electrical connectors look really good. I tried sensors that were running fine in another car. shrugs I'll probably just replace the sensors and hoses again and clean the connectors the best I can and see what happens.
 

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Remember with my van, the MAP issue would not appear until long periods under load, then it would start to fail, go from 3.5 volts straight to zero. I found it when I ran two wires from under the hood into the interior, and hooked up my mm, and watched the voltage. I pulled the rubber grommets back from MAP connector, and just shoved the wire down the connector - one for output voltage, and one to ground. When it would get around 4500 rpm, the voltage would go from 3.5, to zero, then jump back up and down. Then then motor would not rev, as in the video.

If that does not work, try the input voltage to MAP, make sure it does not drop off or fail.
 

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Remember with my van, the MAP issue would not appear until long periods under load, then it would start to fail, go from 3.5 volts straight to zero. I found it when I ran two wires from under the hood into the interior, and hooked up my mm, and watched the voltage. I pulled the rubber grommets back from MAP connector, and just shoved the wire down the connector - one for output voltage, and one to ground. When it would get around 4500 rpm, the voltage would go from 3.5, to zero, then jump back up and down. Then then motor would not rev, as in the video.

If that does not work, try the input voltage to MAP, make sure it does not drop off or fail.
Yeah from the video you had it looked like your van was electrically limiting itself not a mechanical issue.
I bet he has some bad grounds causing the sensors to drop out randomly.
 

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Discussion Starter · #16 ·
So here's what I've tried. I eliminated all manifold vacuum except MAP/BAR, brake booster, FPR, and PCV. (It's pretty hard to disconnect the PCV, but I also swapped out the grommet and even tried zip-tying every joint.) The wastegate solenoid was also still connected. Behavior was about the same, and the buck/surge problem was still present.

I bought a $15 TPS on eBay. It was 0.75v at closed throttle, 3.96v at WOT. However, the computer immediately (and consistently) gave code 24, "Sensor output less than 0.16V or greater than 4.7V". Reinstalling any of the used sensors cleared the code. I then bought a $36 TPS from CarQuest. It did the same thing.

I soldered a new ground from the TPS harness to the throttle body and also to the battery negative. No change.

I replaced the MAP/BAR with a set from another 16v Spirit, and it refused to run. It would sputter and cough, no codes. I put the original pair of sensors back, and it worked "normally".

I'm out of things to try. I'm not doing anything exotic. I'm just trying to get it running STOCK!
 

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1984 Dodge Rampage Turbo
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So here's what I've tried. I eliminated all manifold vacuum except MAP/BAR, brake booster, FPR, and PCV. (It's pretty hard to disconnect the PCV, but I also swapped out the grommet and even tried zip-tying every joint.) The wastegate solenoid was also still connected. Behavior was about the same, and the buck/surge problem was still present.

I bought a $15 TPS on eBay. It was 0.75v at closed throttle, 3.96v at WOT. However, the computer immediately (and consistently) gave code 24, "Sensor output less than 0.16V or greater than 4.7V". Reinstalling any of the used sensors cleared the code. I then bought a $36 TPS from CarQuest. It did the same thing.

I soldered a new ground from the TPS harness to the throttle body and also to the battery negative. No change.

I replaced the MAP/BAR with a set from another 16v Spirit, and it refused to run. It would sputter and cough, no codes. I put the original pair of sensors back, and it worked "normally".

I'm out of things to try. I'm not doing anything exotic. I'm just trying to get it running STOCK!

Measured voltage, is that static; vehicle in park? I would suggest monitor TPS and MAP voltage when it bucks/surges. Run wires into the interior and observe with MM both TPS and MAP. Only way to nail this down is to start observing voltages during the issue. If it surges, then voltage drops, it is not the issue. If voltage drops, then it buck/surges, it is your issue. Process of elimination.
 

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Discussion Starter · #18 ·
Measured voltage, is that static; vehicle in park? I would suggest monitor TPS and MAP voltage when it bucks/surges. Run wires into the interior and observe with MM both TPS and MAP. Only way to nail this down is to start observing voltages during the issue. If it surges, then voltage drops, it is not the issue. If voltage drops, then it buck/surges, it is your issue. Process of elimination.
The TPS test is as in the manual, KOEO. It would be very difficult to catch it while driving, as it's extremely brief and intermittent. I might be able to catch it if I had electronic and video recording at the same time.
 

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Discussion Starter · #20 ·
Off the wall thought.. did you check fuel pressure?
It's been a while, but yes. I can give it another test, though, since other things have changed. I've been tempted to add a boost gauge and wideband, but it seems a bit excessive just for diagnostic to get a stock car running as stock. )-:
 
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