Power Limited Light

[jpp426]

I recently purchased a 85 Laser Turbo. It had been sitting for a while (a year) but documentation showed it was well maintained...i.e., regular tune ups, oil changes, good general all around servicing. It has 125K miles. My problem is that I drove it home and it ran great. Later that week, I got a little froggy and decided to put my foot in it. Well, it boosted up and took off then it shut down. From what I read, hit an "overboost" condition and shut everything down. Once the boost returned to normal, the power limited light had illuminate and it would not rev above 2K and I limped it home. I did my best with my limited knowledge to troubleshoot the problem. Fault code indicated faulty TPS. Disconnected the battery and changed it. Started it up, same problem. I've checked wiring, hoses and everything else that I thought that could cause the problem and I'm at wits' end. One person told me that the exhaust (converter) could be clogged. Any guidance will be greatly appreciated.

[jpp426]

thanks for your help. It seems that it is not worth repairing - off to the salvage yard.

[dwh4784]

Maybe you blew the MAP line off? Also make sure all the grounds are perfect, I was having trouble with the TPS throwing a code and I swapped it out...no change like you said. But I redid all the grounds and that fixed it. Grounds to check are: firewall to intake manifold, passenger side motor mount bracket to body, wiring harness to head(front drivers side), harness to top of transmission and obviously the battery.

[jpp426]

Thanks for the guidance on the MAP sensor. I "looked" at it but didn't do in indept investigation. I will check all the grounds and readdress the MAP sensor. Sounds like a project this weekend. Thanks again.

[GLHSKEN]

Map sensor... I think you mis-read the codes. TPS has no limp in mode. Map limp in mode is 2k rev limit.

JPP... Don't post a sarcastic response if your thread is not immediatly helped... Just bump it up to the top. 85 has the map on the logic module in the kick panel. There is a long vacuum line there... Might want to check that.

[mw6886]

Yes, TPS has a limp in mode.

Just clarifying.

[dwh4784]

Yeah it leaves the PL light on but the 2k thing really sounds like the MAP. I blew my MAP line off once and it acted just like that. And the part about it happening in full boost suggests it too.

[jpp426]

Map sensor... I think you mis-read the codes. TPS has no limp in mode. Map limp in mode is 2k rev limit.

JPP... Don't post a sarcastic response if your thread is not immediatly helped... Just bump it up to the top. 85 has the map on the logic module in the kick panel. There is a long vacuum line there... Might want to check that.


GKHSKEN - I had no intentions of the post being read as sarcastic. If it came across that way, I apoligize. I'm new to this so I ask your (all) forgiveness. It's extremely hot outside today and I will check and replace it if necessary and post the results. Thanks for all the help - it's really appreciated. JPP

[sdac guy]

Yes, TPS has a limp in mode.

Just clarifying.Yep, this is correct, sorry Ken. The TPS fault code is 24, and it will put the car into limp in mode with the power loss lamp on until the condition is cleared.

I agree with the other posts that a vacuum line might well be the problem as it happened while under boost. But also it happened at WOT, so it is entirely possible the TPS is dirty or broken inside.

From the 'instructors guide' "the TPS voltage cannot be below .16 volts or above 4.7 volts. If either of these voltages are exceeded the power loss/limited lamp is turned on. The system is now in limp-in mode and fault code 24 will be stored in the module's memory."

Good luck JPP on solving this problem.

Barry

[GLHSKEN]

LOL You are all correct... Tps does set the light (when it wants to) I should have clarified. The TPS limp in does not affect driveability the way your car is being affected!!! :)

If you reached an overboost condition at higher revs then it would not rev above 2k, you blew the map line off. (or a hold in it. If it's the old hard line, sometimes it's tought to see the crack..

[sdac guy]

LOL You are all correct... Tps does set the light (when it wants to) I should have clarified. The TPS limp in does not affect driveability the way your car is being affected!!! :)

If you reached an overboost condition at higher revs then it would not rev above 2k, you blew the map line off. (or a hole in it. If it's the old hard line, sometimes it's tought to see the crack..

A couple of things here. First off, the TPS fault code 24 always sets the limp in mode and turns on the power loss light (according to the 'instructors guide'). Unless he had a code 45, the engine did not hit overboost. It may have shut down due to the TPS code 24, and he mistook the symptom for an overboost condition. But if it really did overboost, then code 45 would have been set also. Code 45 will stay in memory for quite some time unless it is cleared.

Again, according to the 'instructors guide' the "limp in mode will limit the engine to 2000 rpm when the TPS indicates an opening of 22 degrees or more."

Limp in mode will also limit boost (if attainable at all). If the TPS is the code causing the limp in mode, then it very well may limit engine rpm all the time since it cannot trust the reading from the TPS.

Every time I have had a bad vacuum leak in the MAP line, or have it come off because of boost pressure, the car stalls and if it restarts it runs very badly and stalls again, and code 13, MAP pneumatic error, is set (after trying to restart it). The code 13 is set when, during cranking, the logic module doesn't see a change in the MAP reading. If he doesn't have a code 13, the problem likely is not a vacuum leak in the MAP line. Still possible, but not the likely culprit to this problem.

Barry

[GLHSKEN]

Dammit... O.K. I've had rotten TPS's that never set a code.

Form Mini-mopar

Results If Component Fails
Fault code 24 is stored, the power loss light is turned on, and the logic module will enter limp-in mode. The logic module will then use the MAP sensor as an indication of the thottle position. A MAP sensor voltage less than 2.0V is considered closed throttle and a MAP sensor voltage greater than 2.0V is considered wide open throttle (WOT).



Boost is not limited... But she will spit and sputter on occasion. I've run down the strip like this. Drove home at well over 2k rpm. The map limp in limits you to 2k rpm.

Map limp In from Mini-mopar

Results If Component Fails
A fault code 13 is stored, the power loss light is turned on, and the system will enter limp-in mode. The AIS will then be completely closed and the logic module will use the TPS and the ignition reference sensor to guess what the manifold pressure is. Also, the engine speed will be limited to 2,000 rpm on turbo engines when the throttle plate is opened more than 22 degrees to prevent overboost


BTW... Any other codes???

At this point, I'm confused as hell!!! LOL

[sdac guy]

Dammit... O.K. I've had rotten TPS's that never set a code. That's exactly correct, I do not disagree at all with that. And what is posted on Russ's site is pretty much word for word from the instructors guide.

BUT here's what JPP said in his first post in this thread "Fault code indicated faulty TPS." So he HAS (or had) the code 24. Therfore the power loss lamp was lit and it was in limp in mode. And he said he couldn't get it to rev over 2K. It's in limp in mode! Said he disconnected the battery, started it again, same thing (power loss lamp, won't rev), still in limp in mode!

All I am saying is that it may indeed be a faulty TPS and that is the only problem. IF that is the case, having him chase a vacuum problem is a waste of time. A bad TPS would explain ALL of the symptoms the car has, and clearing that code is the first order of business.

Also, remember this is an 85 which had been sitting for a year. If the battery was dead (or had been disconnected), then the adaptive values in the logic module had all been lost. In that case, overboost for the first few times at WOT is perfectly normal. Once the module re-learns the boost control and sets the adaptives correctly, the false overboost shutdowns should cease.

Barry

[sdac guy]

Also regarding the TPS and possible problems. Since the car was sitting for a year, it may be just a corroded connection causing the problem, and not an actual bad TPS.

Check the connections for the TPS under the hood, and pull the connectors from the logic module, look at them closely for any whitish grey or light bluish corrosion. Also pull out the logic module where the connectors on it can be examined up close. Clean any pins/connectors thoroughly that appear to have any discoloration.

The logic module is the one located under the passenger side kick panel in front of the door.

Barry