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post #1 of 26 Old 02-16-2017, 02:08 PM Thread Starter
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Unhappy Strange new driving sensation (86 GLHS)

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
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post #2 of 26 Old 02-16-2017, 03:08 PM
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Re: Strange new driving sensation (86 GLHS)

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.
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post #3 of 26 Old 02-16-2017, 03:08 PM
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Re: Strange new driving sensation (86 GLHS)

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

86 GLH S60
86 GLHS 373
89 Turbo Minivan
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post #4 of 26 Old 02-16-2017, 03:09 PM
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Re: Strange new driving sensation (86 GLHS)

Hi Todd !!!

Thanks
Randy
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post #5 of 26 Old 02-16-2017, 03:10 PM
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Re: Strange new driving sensation (86 GLHS)

Quote:
Originally Posted by Glhs60 View Post
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
Haha tree'd you Randy. Reaction time FTW!!! hehe
Todd
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post #6 of 26 Old 02-16-2017, 04:31 PM
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Re: Strange new driving sensation (86 GLHS)

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.
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post #7 of 26 Old 02-16-2017, 05:47 PM Thread Starter
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Re: Strange new driving sensation (86 GLHS)

Quote:
Originally Posted by Glhs60 View Post

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?

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post #8 of 26 Old 02-16-2017, 06:22 PM
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Re: Strange new driving sensation (86 GLHS)

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

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post #9 of 26 Old 02-16-2017, 06:26 PM Thread Starter
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Re: Strange new driving sensation (86 GLHS)

Quote:
Originally Posted by 4 L-bodies View Post
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.
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/d...ckup+coil,7176

Thanks all for the tips on where to get started.

Skyroof
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post #10 of 26 Old 02-16-2017, 06:47 PM Thread Starter
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Re: Strange new driving sensation (86 GLHS)

Quote:
Originally Posted by Glhs60 View Post
Right.

As mentioned, a hanging Engine idle, especially when slowing to a stop can be speed sensor related.
A hanging engine idle? Haha. Yep. Got that too. Been with the car since I bought it. Guess I need a speed sensor too.

Anybody know if Standard Motors Products part # SC5 correct? Only one Rock Auto carries.

1986 DODGE OMNI 2.2L 135cid L4 Turbocharged Speed Sensor | RockAuto

Thanks.

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post #11 of 26 Old 02-17-2017, 06:24 PM
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Re: Strange new driving sensation (86 GLHS)

Quote:
Originally Posted by Skyroof View Post
A hanging engine idle? Haha. Yep. Got that too. Been with the car since I bought it. Guess I need a speed sensor too.

Anybody know if Standard Motors Products part # SC5 correct? Only one Rock Auto carries.

1986 DODGE OMNI 2.2L 135cid L4 Turbocharged Speed Sensor | RockAuto

Thanks.

Skyroof
I'm surprised your original sensor lasted this long. The wires usually became brittle and would break. Mopar 5227896 is correct part # but completely different looking than your original sensor. This also requires you to use a small 6" pigtail wiring harness adapter that probably is no longer available at Mopar. Back in the day, they included these pigtail adapters with VSS purchase. Just make sure whatever one you buy, it has threaded nipple for manual speedo.
Someone on EBay was selling NOS VSS for $20 a while ago. I stocked up (lol). You might check there or Google that part #.
It's very possible that your 86 GLHS already has had the newer VSS installed. If that is the case, then the wiring pigtail will already be installed.

Todd
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post #12 of 26 Old 02-18-2017, 12:31 AM Thread Starter
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Re: Strange new driving sensation (86 GLHS)

Quote:
Originally Posted by 4 L-bodies View Post
I'm surprised your original sensor lasted this long. The wires usually became brittle and would break. Mopar 5227896 is correct part # but completely different looking than your original sensor. This also requires you to use a small 6" pigtail wiring harness adapter that probably is no longer available at Mopar. Back in the day, they included these pigtail adapters with VSS purchase. Just make sure whatever one you buy, it has threaded nipple for manual speedo.
Someone on EBay was selling NOS VSS for $20 a while ago. I stocked up (lol). You might check there or Google that part #.
It's very possible that your 86 GLHS already has had the newer VSS installed. If that is the case, then the wiring pigtail will already be installed.
Actually, I am not very surprised at the sensor lasting this long. This car only has about 1300 miles on it since 2002 and 102K overall. It sat from 2002 - 2014 & again in 2015 - Fall 2015. When I have time and weather cooperation, I have been sorting things out after its long slumber.

I will check and look around to see if a MOPAR VSS exists for sale anywhere. If not, I will have to turn to the RockAuto part.

Thanks for your input. Much appreciated.

Skyroof
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post #13 of 26 Old 02-18-2017, 06:09 AM
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Re: Strange new driving sensation (86 GLHS)

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.
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post #14 of 26 Old 02-18-2017, 02:28 PM Thread Starter
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Re: Strange new driving sensation (86 GLHS)

Quote:
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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.
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
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post #15 of 26 Old 02-18-2017, 03:36 PM
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Re: Strange new driving sensation (86 GLHS)

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.
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