LHS help from a Chryco tech....

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redlined

redlined

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My '97 LHS has a miss. 3.5 V6. Engine's in good shape, even comp across the cyls, uses no oil, plug color looked good etc. Has about 95,000 miles, been garaged/pampered since new. Had a little putter at idle to begin with, has progressed to a noticeable miss under load. Gas mileage has dropped 3mpg {27 to 24} and the torque is down too. Lost it's pep.

Had to replace the injector O rings, so while I had the upper plenum off I replaced the injectors, plugs and wires, as these were all OEM. Still had the putter at idle. It soon progressed to a miss under load, I then replaced the coil pack as well, to no avail. I can find no vacuum leaks. I can feel the miss at idle in gear now.

I have an old SnapOn scanner, has no codes. By initiating an injector kill test the putter disappears, smooth as glass. This is open loop, correct? Any suggestions where to look next?
 
i worked as a dealer tech for 17 years,two problems that cause that where lower intake,the gasket would split causing a vacuum leak . some times if you spray carb. cleaner under the intake,below thermostat area of lower intake.some time though you have to just pull lower intake and look for carbon tracking from split gasket. the other problem was the egr valve . this also easy to test .the two tubes comeing off egr to top of intake,can be pluged by inserting a sheet metal plate between gasket & upper intake.if car run better,bad egr. pm me and let me know what you find
 
What I'd like to know is what does commanding an injector kill test have to do with smoothing the idle? I get a marked difference on cyls killing injectors, but with all 6 on, the idle goes butt smooth, no putter/miss.
If it goes open loop when the kill test is commanded, then something under computer control is causing or aggravating the problem.

Back to the EGR possibility? I assume this setup uses an EGR position sensor?



No lifter noise BTW, and engine is very clean inside. The oil's never been dark. IMO, if it ain't clear as when it came outta the jug it needs changing.
 
Killing the fuel to the effected cylinder will stop the fire and prevent the exhaust from being shoved back up the intake. This would help get rid of a sputter caused by the reverse flow. Check the Exhaust lobe or follower!! Or don't listen it don't matter to me . Been there on several motors. If you say you checked everything you did what else could it be. If the exhaust valve doesn't open it will still show compression. It still draws air and fuel and it still seals off on compression stroke so it fires. Just that when the intake opens the exhaust goes out that way. Shut off the fuel and you don't get the explosion to cause the back flow.
 
Oldmanmopar said:
Killing the fuel to the effected cylinder will stop the fire and prevent the exhaust from being shoved back up the intake. This would help get rid of a sputter caused by the reverse flow. Check the Exhaust lobe or follower!! Or don't listen it don't matter to me . Been there on several motors. If you say you checked everything you did what else could it be. If the exhaust valve doesn't open it will still show compression. It still draws air and fuel and it still seals off on compression stroke so it fires. Just that when the intake opens the exhaust goes out that way. Shut off the fuel and you don't get the explosion to cause the back flow.[/QU


Ok, I won't since you can't comprehend what I've written. Not killing any injectors, just going into kill test mode, which is open loop and commands a preset ignition timing/pulse width to stabilize RPM. Back out of the kill test mode into closed loop, the putter comes back and RPM drops. A mechanical malfunction would be apparent regardless of computer mode, not to mention the fact I've replaced enough flat cams in Chevy small blocks to recognize the symptoms.
Click to expand...
 
the 94 JY was having some weird idle issue and sputter under load... O2 sensor was toast... i mean weird issues, would just freak out and start stalling and then pick up again after loosing 10 or 15 mph, idle would be anywhere between 500-1500 as well...
 
the 3.5 was know for lower intake gaskets leaking and egr valve problems . i would check them. o2 sensor you would see stuck with scan tool.
 
redlined said:
What I'd like to know is what does commanding an injector kill test have to do with smoothing the idle? I get a marked difference on cyls killing injectors, but with all 6 on, the idle goes butt smooth, no putter/miss.
If it goes open loop when the kill test is commanded, then something under computer control is causing or aggravating the problem.

Back to the EGR possibility? I assume this setup uses an EGR position sensor?



No lifter noise BTW, and engine is very clean inside. The oil's never been dark. IMO, if it ain't clear as when it came outta the jug it needs changing.
Click to expand...

no egr position sensor on this car,just vacuum transducer
 
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