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need help fast!

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05silverado4x4

New member
I am working on a family members 1999 gtp. has a tuned pcm, cai, and 3.4 pulley. it ran like crap when he brought it to me, so I pulled the plugs out and found an electrode on one plug was broke. so replaced all plugs with ngk tr55's and a new plug wire set. ran awesome for a while. when I went to start it up later tonight the temp light was on and the temp gauge was stuck at 180 degrees and didn't move at all, the engine was cold so I know the temp gauge should not have been that high nor the temp light shoulda been on. now the temp light and gauge are stuck on and at 180 degrees. after driving it a little more the engine became sluggish and had NO power... with the pedal floored I could barely make it up hills. I thought it may be a limpmode, so I disconnected the battery for a while and tried it again and the same problems occur. when I first start it up the engine runs fine but then after maybe 15 seconds it starts running rough and has no power/sluggish. what could be causing this?... coolant temp sensor? plugged cat? egr? bad ecu? im lost. im a mechanic, but just figured maybe someone here has had this problem and knows what could be causing it off hand. need to get this fixed asap. I will put a backpressure gauge on the upstream o2 tomorrow morn to see if cat is plugged and maybe clean the egr and check for any vacume leaks. im just stumped lol :th_scratchhead:
 


Maybe the cats plugged, but we have a bigger problem I bet.


If this car has that 3.4 pulley with no other supporting mods like exhaust wise, say headers, downpipe or a powerlog from manifold, I' say we have atleast 1 chipped piston with that spark plug tip being broke off.
 
chipped up towards the top of the piston? I have a bore scope I can go into the cylinder and inspect the pistons. like I said tho, the car runs and drives perfectly fine for like 20 seconds then its almost like it goes into a limp mode and just have no power at all. and even at cold start the temp light is on and temp gauge reads 180. but that broken spark plug tip still does scare me that something else may be wrong piston wise like u guys are stating
 


okay I will bore scope all the cylinders and see if any pistons are chipped. if they are all fine where should I start? replace the coolant temp sensor to get the gauge and light working again?
 
Yes..

And I'd scope that one cylinder that had the bad plug. Because either it predetonated and blew the plug apart, the plug was ancient or something whacked it.
 


well just took itfor a drive right now, drives fine, tons of power and no temp light....? wtf. it was raining yesterday so maybe the water got into something electrical andmessed it up till it dried out? maybe a coil is going bad and was heatsinked? now im lost... lol
 
so I found a few wires I didn't like, fix them up and cleaned some connections. drove it around for quite a while today and ran awesome. hope it stays that way. I will still do some more wiring harness inspection just incase. also I replaced the ect sensor, and when I first started it up after I installed the new sensor the temp gauge was peged as high as it can go. did I get a faulty sensor?
 
Either that or the wiring to the sensor is messed up somewhere.

Also, I would be swapping back to a stock pulley if you have no way to scan for KR right now or you are just asking to replace this motor. Since there are no flow mods as mentioned it could just be a matter of time before a piston goes bye-bye. If it's running ok for now minus the temp gauge issue then I would say it gave you a 2nd chance, don't let it go by.

Also, what is it "tuned" for?
 
ok I will check the wiring to it. it is not my car, so not sure what it is tuned for. all I know is it has a smaller supercharger pulley and an intense racing tuned pcm and cai. also I was looking at the exhaust today when I had it up on the lift, the manifolds are stock but the down pipe looks a lot bigger than stock, and from the downpipe back to the muffler there is a new straight pipe, that tight bend in the exhaust was eliminated.
 


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