[benvanderjagt]

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!

 

[benvanderjagt]

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.

 

[benvanderjagt]

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

 

[benvanderjagt]

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.

 

[benvanderjagt]

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."

 

[benvanderjagt]

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??"

 

[benvanderjagt]

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.

 

[benvanderjagt]

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.

 

[benvanderjagt]

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!

 

[benvanderjagt]

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.

 

[benvanderjagt]

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. )-:

 

[benvanderjagt]

The speedo seems good. If I were to guess based on performance, the mixture is wrong most of the time. It smells rich. Once in a while (usually after fiddling with stuff around the TPS), it drives great for a little while, very responsive, smooth, and powerful. In other words, it feels like it reads the TPS right sometimes and wrong most of the time.

 

[benvanderjagt]

I'm trying to do little things at a time, since it's an intermittent problem with strange nuances. So, here's what I've done. I swapped out another MAP/Bar set, and nothing changed. (Previously, a known good set made the car basically not drive at all.)

I attempted to remove the O2 sensor. It's a new Bosch sensor, but then again I have two new TPS's that don't work at all. I noticed that keeping a very exact throttle during acceleration had a specific behavior: Smooth torque for a second, then misfiring for a second, then smooth torque for the duration. That made me think it was incorrectly adjusting to the mixture it was seeing go out the pipe. Unfortunately, it's very stuck. I may try that tomorrow. I have an almost new Mopar sensor I can try.

I haven't yet tried unplugging the speed sensor. I discovered that it does in fact happen across all speeds. I also haven't done the vacuum idle RPM check as described above.

Here's the interesting thing. I change the TPS yet again! The buck/surge when closing the throttle plate is there, but now I have smooth solid acceleration across the RPM range. The exhaust eye-burn seems to be gone, too. Oh, and get this. This TPS reads 1.6v when the throttle is closed! It's a Holley (stock) from out of a 2.5 Turbo. shrugs This TPS is way wrong, but the computer likes it, and it drives great.

I've still got to try driving with the speed sensor unhooked, and I also still want to install the boost gauge.

I had yet another theory about all the madness. I notice something very strange about the temp gauge. As soon as the temp starts to rise into the normal operating range, the tach starts to work. I assume that has to do with the cluster. However, when the engine is showing full operating temperature, the buck/surge problem is either minimal or gone. It's almost never at full operating temp...or at least is rarely SHOWS that. The previous owner had simply removed the thermostat. I installed a 185 degree thermostat. I expected to see the needle stay up higher, but it doesn't. I was under the impression that the coolant temperature sensor only controls the fan and the block temperature sensor only shows a readout on the cluster, and the O2 sensor gives it the feedback whether to choke or not. Could it be that one of these sensors is bad and causing it to stay rich? I did once see the "temperature stayed too low for too long" code before installing a thermostat, so I know the car is capable of determining that, but I haven't seen it ever since installing the thermostat.

 

[benvanderjagt]

Try swapping the temp sensor. I tried 4 of them till mine ran right. The bad ones had the connector spin side to side if u twisted it.

The single screw one or the two pin one?

 

[benvanderjagt]

I feel like I'm writing a bad comic about a demon-possessed car.

Disconnecting the speed sensor doesn't seem to have an effect, other than getting a code.

I replaced the O2 sensor. The old one seemed good, but a faulty O2 sensor would have made sense. shrug I tested the old coolant temp sensor. At full operating temperature, it should read between 100 and 1000 ohms. It read 984. After much delay cooling and warming back up, I replaced it with a new one, which also reads about the same. I deleted the BOV, and that solved the inconsistent power problem. (It seems they're all bad. Meh, I'll probably just leave it off. I'm sure the big ol' Garrett can eat the boost just fine.) Keeping in mind, the problem I'm trying to solve is still the power surge when the throttle plate closes, so even a faulty BOV sorta kinda could make sense if it's letting the boost out when the throttle opens and the turbo is spooling up, then closing the throttle closes the BOV and suddenly there's boost hitting the intake....but alas, that does not seem to be the cause either.

So....I went for a test-drive after changing the (apparently good) O2 sensor with another O2 sensor, and it threw a fireball out the intake! Fortunately, the radiator spontaneously started spraying coolant to put out the fire.

The key dance gave 12, 53, 24, 24, 55. I did it twice to make sure, and both times it gave code 24 twice, which is bad TPS.

Got it back into the garage and replaced some EXPLODED vacuum lines and fixed the coolant leak. I couldn't find anything else wrong, so I went to do several test drives, and it's been running perfectly. 🤬

 

[benvanderjagt]

Nope, I've pulled (and replaced) the injectors on the rail with pressure still up and it's always clean.

 

[benvanderjagt]

Ah, gotcha. I don't think that's what's happening. I'm sorry I neglected to mention the misfiring, stutter, and rattle that preceded the bang by a fraction of a second. I think the computer's interpretation of timing went waaay off for some reason. Everything on this car has been a mystery. The bigger mystery is why it runs flawlessly now. It's consistently responsive with smooth boost gain and easy control at low speeds. The buck/surge problem hasn't come back since the explosion either.

 

[benvanderjagt]

What was holding it together, positive thoughts? Wow! Then again, my Shadow's TEO4H turbo had no v-band clamp, and that sucker ran STRONG!

 

[benvanderjagt]

Have I already said that I hate this car? I hate this car! I love this car! Okay, I hate it too...but just in sheer raw performance, this thing is unreal! I've been taking as many side trips as I can, and it's still driving very very well. (It has a momentary hesitation at low throttle, but it hasn't bucked once. Also about one in twenty WOT pulls doesn't feel like it boosts at all. That might be a weak wastegate, boost hunching, not sure. These are subtle, ignorable, and probably just minor out-of-spec issues.) Apparently the car just needed to be flame seared like a steak one time.

It pisses me off to not know what the problem was, but if I were to hazard a guess, it was probably a blocked/cracked/leaking vacuum line that I hadn't detected before. I'll update if the problem comes back. shrug

 

[benvanderjagt]

Turbo-III is just not good.

The buck/surge came back, and power disappeared again. Now it also occasionally stutters and stalls out, feeling a lot like the ignition system is repeatedly turning on and off. I did get another code 24, and THIS time I got a 3v reading at closed throttle, which means it wasn't making good contact with the TPS. Sure enough, the NEW connector stopped making contact with the TPS, no matter what angle I held it at. I also tested the Holley TPS I had in there (the one stolen from the 8v Spirit), and surprise! It was bad! It reads zero ohms at closed throttle. I took a TPS that tested good and I soldered that motherfucker in. Now there's no TPS code, but the buck/surge is constantly there, and power is poor.

Also I seem to have broken 3rd gear. It doesn't feel like there's anything to engage there, and it just pops back into neutral when I try. 1,2,4,5,R all work.

Screw this car. I'm selling it to try to get back my losses. Three Spirit R/T's, $10k dumped in, not one good running 16v example.