If this is previously been covered elsewhere I apologize. Hope the seasoned Vets here can help me out. 99 2.4 LD9 grand am SE. on the clock is 160K miles. At 96K it had the following engine work done.main bearings replaced, Oil Pump Replacement, head work, including 3 angle valve job, new lifters, water pump, timing chain, possible upgraded cam ( not sure i don't see any GM part numbers on it, and the lobs look pretty aggressive) Current mods are Pace Setter headers, Weapon R cold air intake, CAT delete, and Exhaust.
About 2 weeks ago, i was at a red light, and all of the sudden started running extremely rough, and died. Got it to fire back up, under throttle only, and barely made it 1.5 miles back home. She was back firing out the exhaust, jumping, misfiring, you name it. No CEL was triggered. Given the symptoms, i assumed it jumped a tooth, and the timing was off. Upon inspection, it looked like the timing chain tensioner failed, allowing the chain to jump. Since this was beyond my skill set, i tasked the work out to my buddy who is an ASE mech. After he replaced the timing chain, tensioner, ect its still running rough, and vapor locking. ( now im getting a flashing CEL) I assume, or thought, that he didn't time the motor properly.. He said you bent a valve, so top end tear down began... Everything looks great. cams, lifters, valves look, perfect. Side question, do any of you know if the stock cams have GM part numbers on them? He strongly feels the cams have been upgraded, but im not 100 percent certain. I cant find any GM part numbers on the cam.
Any feed back here would be greatly appreciated. Im spending money, and not getting any where. Thanks in advance.
Any one? would be appreciated ?
Ignition coil pack housing shorting out inside of it will cause these symptoms. I think that the white ones are better than the black ones. If for no other reason you can see the scorch marks when they begin shorting in the white ones. This is an easy and not too expensive of a fix if it is what your problem actually is. The backfiring is probably from unifnited fuel in the exhaust from only 2 cylinders firing as a result of the failing housing.
I used to have a 96 Cav LS with the LD9 and that happened to me once and interestingly my son had a 99 GrandAm with this engine as well. I had all of the same symptoms and like with you had to keep my foot heavy on the gas just to get mine home too. I am sure it was not good for the cat as could be seen from all of the rich smoke coming out. For me, it was the inside 2 cylinders not getting spark and compression testing revealed much lower pressures due to the fuel wash. Adding oil in the spark plug holes and retesting restored compressing indicating the lack of a spark. When the coils tested out ok I then noticed th Brian run marks in my coil pack housing. I also checked on the quad 4 forums and realized this was the likely culprit. A quick replace with a new one and I was back in business.
If someone looks hard on the old quad4 forums they can probably find my posts on this incident from over 10 years ago now. I think I was "96DOHC" on there.
The plain Jane ln2s (unmodified) are certainly less fun to drive than with the LD9 but are so much better behaved and nearly bullet proof. I prefer them now.
Still, if this is what your problem is, your engine should start right up like nothing happened (as long as you don't get unlucky and buy a defective new housing out of the box - this has also happened to people) after you install the new one.
If you take care of your LD9 it should give over 200k miles maybe more since you got that new timing chain and water pump job recently completed. Mine ended when it got crashed...
This is my initial diagnosis. Good luck.
Typing late at night on an iPad while on travel instead of on a real computer keyboard will produce lots of interesting typos but hopefully you can still understand.
Thanks for your reply!
" ignition coil pack housing shorting out inside of it will cause these symptoms" i did replace both coils about 6 months ago.. So what your suggesting is that plastic spark plug boot / adapter will cause this issue? I did test and make sure that all plugs were getting juice previously. I'll inspect it again to see if there's new indication of bleeding spark. I have to reassemble the top end, and install the new gaskets.
I'm going to pick up a new housing from Advance auto. Keep you posted!
Most likely not the boots but the actual plastic housing assembly that looks like an upside down early 20th century "battleship" that you are about to purchase. These things get heated up and are subject to polymeric degradation and embrittlement. Since any scorch marks are typically black, any degradation(s) is much more visible and easy to spot on the white ones vs. the black ones. That is why I prefer the white ones. I actually still have a spare one of these in my possession even though my 96 LD9 Cav and my son's Grand Am SE are both now long gone.
When (notice I did not say if) the housing shorts out you will completely lose firing on 2 of your cylinders due to it shorting out to itself. When it happened to me there was no check engine light at all. It was near impossible to start and ran totally rough just like yours because it was only running on 2 cylinders. For me it was the 2 inner cylinders that were sparkless and when I checked, the compressions were reduced way down due to the unburnt fuel washing out the oil. Prior to figuring out it was the housing I added oil to the 2 low compression cylinders and rotated the engine by hand and found the compression values were restored indicating an ignition based problem and not a blown head gasket which is what I had initially suspected. (Also no coolant in the engine oil was a good sign though the fuel getting into it it was definitely altering it and making it stink of gas)
I hope this is what your problem is because it is very cheap and easy to fix.
For me I went from thinking my car was dead for good to feeling like I scored a free car all in a matter of a few hours.
Please report back whether this was the problem and if the fix worked.
DAMN! I left out a very important piece of information. would the raw fuel loading up cause the engine to vapor lock? I CANT BELIEVE i forgot to mention that in my initial thread. Every other symptom is EXACTLY the same as you described with your car. ( Ive started to assemble the top end) I'll keep you guys posted.