Thread: 99 GTP runs fine cold, seems to lose a cylinder when up to temp?

Hi Guys,

I'm new to these forums, thanks for having me. I've had my '99 GTP for about 5 years now, it's been really good to me but within the last couple of weeks it's been running rough, it seems to lose a cylider once the engine comes up to normal operating temp., it runs fine on a cold start but as seen as it gets up to temp it seems to lose a cylinder, no engine lights come on at all when the cylinder dies. I did some poking around here earlier, someone mentioned that the ICM located under the coil assy can malfunction under these conditions? It's a consistent problem and since it seems to run fine for the first few minutes after a cold start it would lead me away from wire leakage/bad plug/clogged fuel injector?
Someone else mentioned it could be a sticking valve, possibly the valve stem/sleeve swelling after heating up and ulitmately sticking at higher temp? I put a can of Wynn's engine tuneup in the crankcase to try and free up the valve (if it is the valve), it's been a couple of days and I haven't noticed a difference, its' still doing it...

Any suggestions?

Hi Lawngoose,

Thanks for the reply, I do plan on changing the wires/plugs this Friday, I have a buddy that's going to help me. I've never had the wires/plugs changed since I've owned it, is there a tutorial posted in the forums on how to do it? I've changed them a few times on previous cars but never this one, is it difficult to do for this particular engine?

Thanks!

Originally Posted by bluegtp91

Fronts will take about 5-10 minutes...the rears...a different story...get some ratchet straps and pulling that thing forward after taking the dog bones off will make it a breeze. Then, run your 2,4,6 wires under the blower snout for a much cleaner engine bay look.

Thanks for your input bluegtp91, that seems to be the concensus, start by changing the plugs/wires. I was fortunate enough to have a neighbours friend stop by tonight, he's been a GM mechanic for 30+ years, he advised me to go with OEM (AC Delco) wires and plugs. He instructed me to remove the 4 forward dogbone bolts and then the two lateral mounting bolts on the block, replacing them after the dogbones are removed, then attach ratchet straps and pull the engine forward, he didn't say how far though? He said the lower engine mounts will stretch or even split if they're old? I'm a little concerned...

just don't over do it. Pull the engine forward enough to get access and you be ok.

UPDATE

OK, upon backing it into the driveway this afternoon, I noticed a faint smell of rotten eggs (sulfur), I read somewhere that this may indicate a bad catalytic converter?

Originally Posted by gtpinsc

bad cat... get a whole new downpipe here ZZPerformance get a 3inch pipe, converter is included. 5 years never changed plugs and wires? wtf.

Thanks for the feedback, I know, 5 years (60k miles) is unforgivable, I live in the rust belt so the car is rusting pretty bad, I don't want to put too many $$ into it, especially after this f%#$ing recession...I've done some more reading and I'm going to have my my mechanic check the pressure in front of the cat this Friday, as well as change the plugs/wires, I'll keep everyone updated...thanks guys!!

Originally Posted by 98GTPCALGARY

Cat-less 3" dp = WIN

5 YEARS??????

I'd love to go cat-less but here in Ontario we have to get emission tested every other year to get plate tags, what is the OEM diameter? 2 inch? If I go 3" I'm guessing I'd have to replace everything from the cat back?

Originally Posted by gtpinsc

well since u dont like to change plugs... get iridiums or platinums.

If I bought iridiums or platinums, I fear they'd outlast the car , it has 233km on it and the body is falling apart, pretty bad rust, around here (Detroit rust belt) they use salt on the roads in the winter, en masse. Mechanically, it's been really good to me, I'll change the plugs and wireset on Friday and let you know if there's any difference, my mechanic said he'll test the coils, ICM and catalytic back pressure on Friday, at my request. I described the problems I was having and even he was somewhat perplexed...I'll keep you all updated...thanks guys...

Rotten egg smell means the cat is working, but the engine is running pig rich. Usually smells like that when you floor it multiple times. You must fix your misfire issue before you go wasting money on a downpipe to continue having the exact same problems. Just sayin...

Answers all over the place... Sucks when your trying to get a problem fixed. But if you feel loss of power I would check the CAT first. If you feeling like you lose a cylinder then I would go with plugs, coils, ICM.... Good luck

The CAT IS FINE, it's supposed to smell like that when you have a misfire, some of you guys are just oblivious to the obvious answers. OP if you waste money on a new dp, or a new cat, ect, i will put you on the **** list, that's not a good list to be on. Fix the effing misfire, that's your problem, not a clogged cat. Do any of you people even know what a clogged cat feels like? No, of course you don't. So in that case, shhhhhhhhut-up.

Originally Posted by Turbo4door

The CAT IS FINE, it's supposed to smell like that when you have a misfire, some of you guys are just oblivious to the obvious answers. OP if you waste money on a new dp, or a new cat, ect, i will put you on the **** list, that's not a good list to be on. Fix the effing misfire, that's your problem, not a clogged cat. Do any of you people even know what a clogged cat feels like? No, of course you don't. So in that case, shhhhhhhhut-up.

Posts like that and don't think anyone would care if they were on your **** list!!