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Discussion Starter #1
I got a 1985 Omni GLHS that was running great but suddenly developed a bad misfire. The car runs, but barely drives, it bucks under load. It has good compression and turbo has no shaft play. I've replaced several parts recently, but all from rockauto:
Spark Plugs - several times
Spark plug wires - several times
Coils - twice
Coolant temp sensors - both of them
Power Module
Speed Sensor - still throws a code though
AIS
TPS - I've played with the idle a lot
Also added some seafoam to the tank today to try and clean up the idle and it helped

Has a couple mods:
Vacuum block - added after the misfire developed to troubleshoot, still not sure if the solenoids for the EGR and MAP are any good.
K&N air filter
Big front mount intercooler
Stage 3 Cal from FWD Performance
804 injectors
Manual boost controller
Wideband O2 - likes to sit around 13-14AFR at idle, 10-12AFR when free revving, hits 17+ when it misses
Boost gauge - shows 16-20in/hg at idle depending on if it is missing bad and what RPM it is idling at

I've repaired wiring on the car in several places such as new fuel injector clips, new O2 wiring, new coolant temp wiring, fixed spread terminals at the LM, and even added grounds. I've doubled and tripled checked the wiring, but I'm not above doing it again. Only thing I think it is something in the MAP/CTS/IAT circuit, an ignition issue, or just plain bad fuel.

It rarely throws codes other than 15, 22, and 53. I believe the 22 is from pulling the coolant temp plug to confirm timing though (which is at 12 degrees).

Thoughts on where to start?
 

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First question...
Are there any fault codes stored in memory.
If Yes, Post Back with the fault code #.
If No, you have to determine what the cause of the misfire is, Ignition, Fuel, Sensor Readings, Engine Mechanical.
Start with Basics...
What is Engine Vacuum Reading at the Manifold and at the Map Sensor?
Are the Spark Plugs Fouled?
If Yes, 1?, 2? All?

Post Back and we will go from there.
 

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Discussion Starter #3
I'll answer as many of these as I can for now:
Code 15 is stored any time it is driven.
Code 53 is always stored.
Code 22 was stored, but I have since replaced the CTS - I will let you know if this comes back.

Vacuum reads about 16in/hg when it is idling (poorly and missing). Vacuum reads 20 on deceleration. I'll find out if the MAP vac matches the manifold.
Spark plugs are generally covered in black soot, I'll get a picture of one, but I don't leave the car running for very long under these conditions, so the plug rarely enters the cleaning stage. They are NOT wet. All of them match. I'll also rerun the compression test.

More information and pictures to come.
 

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No significant codes other than the 22 and it is important to know if it returns or if the condition is corrected.
84-86 were not smart engine controllers, if the CTS circuit goes open the controller says "Hey, it is -40 degrees, better add a lot more fuel", if there is a wiring/connector/terminal issue and the controller is not seeing the proper voltage (thinking it is colder than it actually is) you will also be rich.
Corrosion at the LM connectors/terminals is a common problem.
You can verify actual voltage at the CTS and if if correct verifying at the LM using your digital voltmeter and backprobing the CTS connector and then backprobing at the LM (Red Connector Cavity 25, Blue Connector Cavity 23)
85-87 LM Turbo Red.jpg 85-87 LM Turbo Blue.jpg Backprobing the CTS.JPG CTS VOLTAGE CHART 2.jpg

Engine Vacuum is in the Normal Range, just verify it is the same at the Map.
Next would be...
1)Ignition, do you have spark at each cylinder (25 KV Minimum)
You can use the screwdriver trick or an adjustable spark tester.
IGNITION- Checking For Spark 1.jpg IGNITION- Checking for Spark 2.jpg IGNITION - Adjustable Spark Tester.jpg

2)Fuel Pressure
 

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Discussion Starter #5
Thanks for the documents! I'll check the CTS. If the CTS does not read/ohm correctly, where can I buy the correct one for the GLHS?

I have a spark plug tester just like that, so I'll confirm that they all have decent spark. I will say that I've been through several sets of plug wires due to them coming apart when removing from the plug, so it wouldn't surprise me if that hasn't happened yet again.
 

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With the CTS you are checking Voltage, not Ohms, the Voltage = a Temperature.
If the CTS voltage is not correct you then have to determine if the issue is wiring or the CTS itself.
All vehicles TBI and Turbo from 85-95 use the same CTS.
If you want to cross reference the aftermarket parts the Mopar Part # is 5226374.
 

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Discussion Starter #7
I checked the CTS voltage at the sensor and LM, they matched and were correct. Had 5volts going to the sensor and measured 1.95 volts from it when warming up. Jumped from ~1.4 to ~3.8 as well like it should.

I checked spark with a tester similar to the one above. All four cylinders and coil checked out. Bought new plugs to go in after I have confirmed everything else.

I called it a day before I got a chance to look at fuel and managed to tear a muscle in my ankle getting off a boat this weekend, so I wont start working on it again until that heals. Last time I checked fuel rail pressure it was good, however that was quiet some time ago. I'll check the pressure at the rail and if need be I have a Walbaro 255 sitting in a box waiting to go in.
 

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First...
Get Well, here's to a Speedy Recovery!!!

1)We have a running rich/misfire/bucking under load condition.
2)The fault Code 22 has been resolved, Code 15 will only create a stalling on decel problem.
3)Ignition System capability has been verified OK.
4)You still need to verify Fuel Pressure, Map Vacuum/Calibration, Engine Mechanical.
 

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Discussion Starter #9
I had a friend come out to help me check fuel pressure. Static fuel pressure is only 47psi. Drops relatively quickly back towards the pump. Still don't have a good way of checking vacuum at the map. However, I figure I could pull the hose and replace it with fresh vac hose going to my vac block which I know pulls 20psi easy. Going to try to do a warm/throttle open compression test later today.
 

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Well you actually have a fuel pressure issue.
Besides checking fuel pressure and Map at idle you need to look at each when the problem is occurring.
You will need a Vacuum/Pressure gauge for both, total fuel pressure is is a combination of rail pressure and manifold vacuum pressure and to verify map voltage is correct you also need to verify the proper vacuum/pressure is reaching the Map.
 

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Discussion Starter #11
So I replaced the fuel pump with a brand new Walbaro 255. I also changed the o2 sensor and spark plugs. While the car runs "better", it still has trouble and doesn't pull full vacuum at idle, only about 15in/mg. However it will pull 20in/mg on engine deceleration. I then found what I believe to be a bad intake/exhaust manifold gasket. I've got smoke coming from around the furthest right hand side intake manifold bolt, next to the power steering pump. A bad intake manifold gasket would explain the poor vacuum. I thought about spraying throttle body cleaner around the intake manifold to check, but being so close to the hot exhaust might be a problem.

Is there any way to replace these while in the car or is it better to just pull the motor?
 

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Not entirely sure on an 85 but the later years you have to pull the head, manifolds, turbo as one assembly.
 
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