Need LS help opinion on a misfire/stumble - already replaced coils & plugs

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swdobbs

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My 2002 LS 3.9 w/ 95k miles developed a very noticeable miss at idle all the sudden one day after work on start up. It surges at stop lights, running ugly but No code.... yet! It still runs decent, just shakes bad at idle and has a miss at 46-50 mph under light load. Downshifts and pulls hard up past 100mph.

After reading this forum the 18 months I've owned the car, I expected coils, called max ordered motorcraft coils and VCG kit.

Replaced all the coils, no oil on any of them DRY spark plug wells (that must be like winning the lottery to an LS owner), replaced the spark plugs with NGK iridium. Old plugs uniform light tan discolored, none visually fouled, looked like oem equipment autolites platinum.

Still a miss at idle after replacing coils and plugs. I believed I have narrowed the miss down to cylinder #6 (drivers side 2nd from front). Runs just as bad with that coil unplugged, whereas the other coils when unplugged all make the idle and the miss far worse. I checked the spark from the #6 coil blue, pretty good consistent snap on the grounded screw driver compared to the other cylinders. I replaced the new coil with one of the other new coils, no change. I listened to each cyl with the socket extensions pressed to the ear, has a light tap coming from #6, doesn't sound like an injector tick, but I haven't heard one an LS injector go bad only chev LT1's.

So now what.... injector? (old spark plug looked same as the rest)

If it was a burnt valve, wouldn't it run bad all throught the rpm range?

Carbon on the cyl?

What would the veteran LS owners check next or do now?

Dealer is about the only option for a scan, no checker/autozone/auto parts stores that have code readers.

I really appreciate any opinions, I like the car but it sounds like its coming apart at idle.

Thank you.
 
Check the compression on the cylinder and check the fuel injector for that cylinder.
 
vacuum leak

JOEGR has a good knowledge of these cars. I'm not a big fan of NGK plugs myself. Had them in my BMW, not a fan.
 
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Tested the pulse/signal to the injectors, all good. Unplugged each of them to see if there was a difference, same miss at idle each time.

I'm going to throw in the towel and send it in to the dealership..... I noticed an off idle rattle in the pass side front (timing chain). Althought the car has the idle miss it will run off idle all the way thru the rpms well, I'm wondering if I lost a secondary tensioner on the pass side, creating slack in the timing chain when there is very little tension in the chains (at idle). I hope not because I'm not up to that job. I've got a couple hotrods I'd rather work 20 - 30 hours on.

Thanks
 
swdobbs said:
Tested the pulse/signal to the injectors, all good. Unplugged each of them to see if there was a difference, same miss at idle each time....
Thanks
Click to expand...

That test only verifies that the PCM is sending power to the injector. It does not verify that the injector is functioning. The only way to really do that is to pull it out of the manifold and see it spray. (Usually, you just substitute a known working injector instead.)

You verified that you have spark, and we'll assume that it is coming at the right time. That only leaves compression and fuel. The compression test is the easiest/cheapest to do, so lets hope that is the dealer's first step now. If you do have compression, then it's got to be the injector.
 
thank joegr,

I pulled the injector wire connections on the driver side one by one, listened for a change in the misfire, plug it back in run it up a little to clean what idle there was up, pulled it listened again. Noticeable difference on the drivers side injectors as each one was pulled, sometimes it took a couple seconds for the sutmble to get worse. Nice how the injector plug clips break off with a satisfying snap the minute I touched them.

Once I changed to the passenger side, I heard a rattle under the leading edge of the valve cover. I grabbed a couple socket extension put them to my ear and screw driver and tried to isolate the passenger rattle and compare it the driver side..... big difference! Passenger side, is loud compared to the drivers side Damn, that passenger side rattle sounds like timing chain tensioner, thats expensive and I don't have the enthusiam to jump into that this winter. I didn't want to let it idle sounding like that, so I stopped checking the injectors.

Dropped the LS at the dealership tonight, I guess I'll know tomorrow.

Thank you everyone, I'll post an update tomorrow.
 
Yes, I should have warned about the fuel injector connectors. If you look at them wrong, the latch breaks. Ty-wraps are a good work around for this.
 
Joegr,

Just got off the phone with the dealership and.....

The timing chain tensioner on the passenger is failing/has failed and the cylinders on that side are out of time.

That is news no LS owner wants to hear!

Well anyone want to buy a 2001 104kmile LS for $2500?

Has anyone had luck with having a used engine installed (or is that another crap shoot)?
 
I'm very sorry to hear that.
My suggestion (others will likely disagree, and so may you) is to sell (or trade) it and get a 2004 to 2006 LS. (Or, a 2003 if you really want to keep the auto-wiper function.)
 
Joegr,

I've got a couple local talented mechanics that are going to chase down some prices on a 70k+/- used motor and the cost to install.

I've considered a newer LS, but I think I may be done with "newer" vehicles for a year or two.

My wifes 2003 Mercury SUV w/ the 4.6 had a similar timing chain issue, we were lucky it didn't let go on the highway. The difference is it was under warranty... so our $400 deductible covered the $4000+ bill. Its run like a top ever since.

I really liked the LS and I may change my mind but newer vehicles are ONLY a good idea if it comes with a good warranty.

I have a driver/restored 1970 Chevrolet C10 truck with a 1994 fuel injected motor and 700r4 that I'll drive this winter. I may end up putting my 1952 Pontiac hardtop on the road as my second vehicle and use my wifes SUV for trips.

Thanks for the help, guys.
 
BTW, one of the many changes from gen I to gen II is the timing chain tensioners. That said, I understand...
 
swdobbs said:
Joegr,

Just got off the phone with the dealership and.....

The timing chain tensioner on the passenger is failing/has failed and the cylinders on that side are out of time.

That is news no LS owner wants to hear!

Well anyone want to buy a 2001 104kmile LS for $2500?

Has anyone had luck with having a used engine installed (or is that another crap shoot)?
Click to expand...


sorry to hear this, people have done the timing chains themselves on here, theres even a write up, but they do seem to go between 100k and 120k from what i read. i hope i still have some time, im at 90k
 
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