1994 Chrysler LHS Rough idle - cylinder 5

Tiny
LHSDUDE
  • MEMBER
  • 1994 CHRYSLER LHS
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 200,000 MILES
Slighly rough, rythmic idle. If I pull injector connector off cyl 5 no change. If I pull it off of any other cylinder it gets worse. Prior to this I replaced the air filter, all spark plugs, all spark plug wires. Ran 2 tanks premium fuel with inj cleaner thru it. Cleaned the idle air control motor (new style). Spark looks good on all cylinders. No stumble or miss off-idle. No check engine codes.

I tried spraying some carb cleaner around cyl 5 intake manifold but no change. Maybe not enough. Did compression test tonight. All cylinders good at around 160 psi. When I pulled the slightly new plugs (100 kms) to do compression test they all looked pretty much the same.

I suspect the cyl 5 intake gasket but need more proof. Acceleration and gas mileage are still good. Any ideas? I've heard ether or propane.

Thanks. LHSdude
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Friday, April 24th, 2009 AT 2:22 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
What were the compression readings.
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Friday, May 8th, 2009 AT 10:31 PM
Tiny
LHSDUDE
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They were all around 160-165, except for cylinder #3 which was 125. According to Chryslers Service Manual that is still within spec.

I suspect either a bad injector #5, a clogged inj #5, or intake gasket. I tried some carb cleaner around the intake #5 port/gasket area no change. I might try again with the new can I bought.

Do you know if it's possible to replace an injector on this vehicle w/o removing the intake manifold. The book says it has to come off but it looks like it might not have to. I.E. I can touch the 3 screws holding that injector locking clamp in. I need to read the book again.

Thoughts? Thanks!
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Sunday, May 10th, 2009 AT 10:39 AM
Tiny
LHSDUDE
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Forgot to mention something.

Using a 12v power source, engine off, if I apply power to the inj connector I can hear the plunger clicking inside (I assume it's moving). Using a scope I can see the injector wiring providing pulses on the end of the connector. Also, the new spark plug in #5 shows normal signs of combustion when compared to the others.

Thanks!
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Sunday, May 10th, 2009 AT 10:45 AM
Tiny
JACOBANDNICKOLAS
  • EXPERT
What specs does your book show for compression variation? I'm showing 10% difference.
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Sunday, May 10th, 2009 AT 1:12 PM
Tiny
LHSDUDE
  • MEMBER
Sorry for the delay. From the manufacturers 1994 LHS Service Manual, pg 9-70, 3.5L engine,
Compression Pressure = 155-170 psi
Max variation between cylinders = 25 percent

Since 5 of the cylinders are in the 160 range, 25% of that is 40psi. 160-40 = 120psi. So cylinder 3 being at 125 is still within spec, but barely. Also when I pull the inj connector on cyl 3 the idle gets rougher so I know that cylinder is making power. If I pull the inj connector off cyl 5 nothing happens to the idle.

Do you know if the injectors on the odd bank can be replaced w/o pulling the intake manifold off first?

Any other thoughts since I'm not convinced I've ruled out the intake manifold gasket completely yet.

Thanks. Ron
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Tuesday, May 19th, 2009 AT 10:00 AM

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