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Strange new driving sensation (86 GLHS)

2K views 26 replies 6 participants last post by  Skyroof 
#1 ·
All,

I have a GLHS with a stock configuration engine, stock turbo, 3" wastegate, 2.5" exhaust, and stock A-525. After the engine is warm, the RPM's at idle had been sitting at 1100 and was running flawless. Without touching anything under the hood, the RPM's suddenly dropped last week to at a fairly consistent 800 at idle. If I am driving a constant speed in the city, the car starts bucking a little like the engine doesn't want to hold a constant RPM (If I am parked in neutral and bring the engine over 2000 RPM's, I see tach needle fluctuating up and down by several hundred) . I get the same sensation if I am descending a hill in 2nd gear for braking or if I am moving slowly with RPM's low in any gear. Acceleration, boost, and shifting through the gears seem to be normal. The engine does not seem to have any extra vibrations out of the ordinary.

Does anybody have an idea where I should begin looking to solve this problem? Thanks in advance for your help.

Skyroof
 
#2 ·
Check your faults codes. Several can be set without power loss light illuminating. Report back what you find. I know factory tachs are horribly inaccurate, but 1100 RPM at idle when warm is NOT normal idle RPM. Your VECI sticker underhood lists 900 RPM for your vehicle. Could be lots of things like broken/cracked pneumatic line. Better have a screwdriver and extra HEP in the car. Could also be a sign that HEP is about the strand you.
 
#9 ·
I probably won't get to the fault codes for a couple of days. Expecting rain for the next 7 days here and I will be keeping the car covered up.

The idle has been high since I bought the car 5 months ago. I haven't been driving it much since October because of all the rain and no working wipers. I was just beginning to think about lowering the idle some when this problem started.

With OEM Mopar HEPs no longer available, are there any aftermarket brands worth trying? Rock Auto carries several. If I went for the Airtex/Wells HEP, there are two different ones. Which would be correct for a Cali emissions car? Airtex/Wells part #8A9 or Airtex/Wells part #4P1232?

http://www.rockauto.com/en/catalog/...1094576,ignition,distributor+pickup+coil,7176

Thanks all for the tips on where to get started.

Skyroof
 
#3 ·
A code check is always the first thing to check, the key dance is great tool.

Something to consider is the Hall Effect, distributor pickup under the distributor cap.

They often don't show any codes when failing but the loss of tach signal is a clue.

Ironically I find used HEPS to be as reliable as new, new are often faulty.

Any 8V Turbo Engine HEP from 1986 and newer is compatible.

Wiggling the wires at idle can sometimes induce issues.

Check the shutter wheel for looseness while checking the distributor.

Lots of possibility's but this is where I would start.

Good Luck!!

Thanks
Randy
 
#7 ·
They often don't show any codes when failing but the loss of tach signal is a clue.
Loss of Tach signal, as in the Tach works intermittently? About 3 weeks ago, my Tachometer started working intermittently. I thought it was because I drove down a bumpy San Francisco street that almost knocked my fillings loose! Do you mean my Tach problems might also be a clue for a HEP going bad?

Skyroof
 
#6 ·
I had a similar problem with one of my GLH TI cars. I changed the AIS a couple times and then realized the problem was the vehicle speed sensor on the transmission. The originals tend to fail after years of exposure to heat, road grime and leaking oil. The new ones are much better, just make sure you get one for a mechanical speedo cable.
 
#8 ·
Right.

While intermittent HEP issues can be hard to pinpoint a loss of tach signal is a clue.

Easier noticed while driving on a smooth road and the Engine falters.

A quick eye can notice the tach falling an instant before the Engine falters.

Totally unrelated is cracked solder joints on the tach board.

Many tach issues can be resolved by reflowing the tach board solder.

Tach problems on a fine running Engine are often solder issues.

Good tach faltering when the Engine sputters or stalls can be HEP related.

As mentioned, a hanging Engine idle, especially when slowing to a stop can be speed sensor related.

Thanks
Randy
 
#10 ·
#13 ·
if the engine is idling high like you say i would be leaning more towards a vacuum leak than anything else. that car is now 30 years old, and all the plastic vacuum lines and the rubber couplers they attach with are probably very brittle and falling apart. a vacuum leak that is enough to bump the idle up by 200 rpm wont set any codes, but can definitely cause the problem you are seeing.

if possible the easiest way to find the problem is to use a smoke machine hooked up to the brake booster line with the throttle body capped off and watch for the smoke around vaccum lines, intake manifold etc. if a smoke machine is not available you can spray an area with carb cleaner or brake parts cleaner- if you hear the idle change at all there is a vacuum leak in that area. also check the vacuum dashpot on the charcoal canister with a hand held vacuum pump- those have a habit of failing and causing a vacuum leak as well. check the brake booster, and the map sensor while you're at it, same deal- use a hand held vacuum pump, pull 22 inches of vacuum, if there is any drop in vacuum then replace the part. if you do find one leaking vacuum line- replace ALL of them. the plastic line and the rubber couplers are available in most auto parts stores in the "help" section- the black plastic line is "emissions line" and the couplers are usually in the vacuum parts section.

Also a sticking pcv valve can cause this. pull it out and shake it- should sound like a round lead fishing weight rattling around inside of a metal thimble- if it even remotely sounds suspect- replace it.

i would very strongly suggest doing the above first before replacing sensors, as you will end up pulling your hair out if you load up the parts cannon and it turns out it was just a vacuum leak.
 
#14 ·
Thanks for your tips. Your paragraph on how to check the vac lines is very appreciated since I have never had to look for vac leaks on a FI car before. I should have mentioned that the engine was rebuilt & installed in 2012 with all new vacuum, fuel, etc. lines installed by the previous owner since most of this stuff was ripped out when he got the car. So not dealing with 30 year old lines here that I know of. It passed Cali Smog in September, so everything was working right at that time (the idle was high during the test). Other than trying to get a handle on fluid leaks on untouched old components, I have not had to touch anything on this engine until now.

I am going to start by replacing the current HEP since I don't a lot of faith in it given the description by others in the thread and that it is likely at least 15 years old. The speed sensor is likely also pretty ancient.

I also own a Honda CRX Spyder. Carb'ed Hondas are the 80's epitome of vacuum lines, so pulling hair out is nothing new.

Thank-you much!

Skyroof
 
#15 ·
you can also try resetting the IAC. start the engine and allow to warm up to full operating temp, unplug a vacuum line to cause a high idle- around 1500-2000 rpm, wait 2 minutes, unplug the IAC and then turn the key off. then plug in the IAC and restart the engine. the computer will try to fully close the IAC when it sees the high idle , the above procedure will do a complete reset.

you can also remove the IAC and plug the hole in the throttle body with something, start the engine and allow to warm up to full operating temp and see where your idle is- should be at 900 with the hole plugged and engine warmed up. this will take the IAC out of the equation in relation to idle speed.
 
#16 ·
Rain has finally stopped, so had a chance to uncover the car and check for engine fault codes. Pulled a Fault Code 33 - AC Clutch Relay Circuit Open or Shorted. This is no surprise since the AC components have been removed from under the hood. So no fault codes worth mentioning.

Going to start with the HEP. With OEM unavailable, I went with a BWD - bought two after reading that 50% of aftermarket ones are bad. I won't have time tomorrow to work on it and more rain coming in over the weekend, so I probably won't swap the HEP until next week.

OHNOTAGAIN - Noted about possibly taking a look at the IAC. Thanks for the suggestion.


Skyroof
 
#17 ·
New HEP installed. The car started strong with the cold idle sitting around 1400 - much stronger than the sputtering 800 on start up I have been getting of late. Idle after about a minute dropped to about 1100 RPM. After the engine warmed, the idle settled down to a lumpy 900 - 1000 RPM. The high rev hanging idle when coming to a stop is completely gone and the "light bucking sensation" at steady driving pace has mostly disappeared. When just revving the engine without gears engaged, the RPM's have stabilized with no floating up and down. RPM's at idle are fairly steady with no bouncing up and down with only the normal 2.2L coarseness.

The only disappointment was my Tach, which is still flaky. So unless it is the solder in back needing touch-up, I am not sure what else it might be.

With the hanging idle seemingly gone, I am going to skip replacing my speed sensor for now. BTW. The BWD (Borg Warner) Speed sensor I bought looks identical & have all the exact same placement of the stamped numbers as the OEM Mopar one on eBay, but the numbers stamped are different. The BWD has the adapter wire harness in the box.

Thanks to all for your help and suggestions.

Skyroof
 
#18 ·
Problem is not solved. Today while driving, the car began to buck again. Lower speeds, especially when driving a constant speed in slow traffic where the RPM's are around 1800 - 2000. Give it more gas and the problem disappears. I check the wires for consistent spark to the plugs using a timing light and feel steady exhaust coming from the pipe. But lightly giving it throttle from under the hood, I can feel that there is a lower RPM spot I can hold it where I hear the engine RPMs shifting up/down rapidly. Any ideas? Clogged injector? Or should I start the hunt for a vacuum leak?

Hanging idle problem is now gone.

Skyroof
 
#19 ·
key on engine off probe the wires of the TPS with a dvom, ground and signal wires. very slowly move the throttle open and closed, paying particular attention to the area of throttle blade movement where the problem occurs. if you notice any spots where the voltage does not change, or appears to flake out or suddenly jumps up then back down or dissapears then you have a bad TPS sensor that needs to be replaced.
 
#20 ·
Okay now that you've checked the obvious, now unplug the vacuum line (source) at your EGR valve, and plug the line, and retest. Sounds like EGR valve is opening when it shouldn't and is creating a lean condition right off idle. This just happened on my friends 86 well preserved GLHT he just bought.
 
#21 ·
UPDATE: Disconnnected the battery, removed the airbox, and replaced the VSS/Distance Sensor. After reconnected everything, the car started strong and ran well initially. The speedometer was working fine. After the car warmed, the tach suddenly cut out and the car suddenly was accelerating poorly. This was especially noticeable above 2700 RPMs.

After getting the car home, I verified spark to each plug using a timing light. I pulled up the fault codes of 12 (Memory standby power lost) and 15 (Vehicle Speed/Distance Sensor).

To date, I have replaced the HEP and the VSS (both with aftermarket BWD units).

Anybody have a clue what is going on with this car? Could the new HEP be a bad unit?

Skyroof


P.S. VSS had been replaced before. It had the later pigtail on the old unit. I used the new pigtail that came with my new VSS.
 
#22 ·
Had a little time this evening. I swapped in another new aftermarket HEP. This time upon starting the car, the RPM's fluctuated wildly, from 2200 to 600 while cold. Still skipping or missing when I throttle up. Thinking this is either a vac leak or I need to replace the throttle position sensor. Will spray some carb cleaner around to check my vac lines tomorrow. If I don't find a leak, a new TPS should arrive by Saturday. And since right there, I will change the AIS as well to eliminate that as a question.

Any other thoughts than the PCV or EGR? Thanks.

Skyroof
 
#23 ·
Randomly changing parts is rarely successful but can be very frustrating.

I try to pinpoint the problem whenever possible, eliminating things one by one.

I always eliminate the PCV system entirely for other reasons.

You could remove the PCV valve and plug the vac hose with a bolt.

Assuming the hose isn't cracked this will eliminate this system for diagnosis.

Don't block the valve cover nipple as the Engine crankcase must be able to breathe.

A section of heater hose can be attached to vent any oily mist away from the Engine.

EGR can be bypassed similarity by eliminating its vacuum source.

Note: EGR stuck open will not idle properly even with its vacuum source removed.

AIS can also be bypassed and idle speed set manually with the secret screw.

A spare AIS must be plugged into the harness to satisfy the L.M.

So now you should have a steady idle, say 900 that will not fluctuate due to AIS issues.

Then it's on to issues not related to AIS, EGR or PCV.

My diagnostic methods are not "in the book" but have been satisfactory for many years.

It's very hard to diagnose online but lots can be learned by the old farmer"cut and try"!!

When and if you figure out the main issue you can restore each system one by one.

It can be very rewarding to actually pinpoint a problem with understanding.


Good Luck!!!

Thanks
Randy
 
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#25 ·
Randomly changing parts is rarely successful but can be very frustrating.

I try to pinpoint the problem whenever possible, eliminating things one by one.
Randy,

You are right. Getting a bit ahead of myself. Thank-you for the check. My prob is I lack trust in the electrical sensors given this car's long outdoor baked slumber.

Next is to check for a vacuum leak. The hoses are new, but it seems to make sense to verify this system is functioning correctly. This will be followed by a PCV system check then an EGR. Will keep the thought of a ground problem in the back of my mind.

My VSS was wet with coolant - a product of a not near tight enough hose clamp. Given I had remove the airbox and plumbing to access, I decided it best to change the VSS while I could see it and physically felt well enough to reach it (won't go into that here).

TPS & AIS will remain in their boxes. They will remain as part of a stock of small parts I intend to carry if taking an extended future road trip.

Onto checking for a vac leak.

Skyroof
 
#27 ·
Update: The remaining power loss issue is now solved. The culprit appears to have been a gummed up fuel system. Two consecutive tanks of gas with a bottle of Techron added has cleared up the remaining power loss issues. I will change the fuel filter after this second tank runs down some.

Thanks again to everyone for your suggestions and help.
 
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