Backfiring, Smoking, Ready to Sell Car (just looking for ideas)
03-25-2009, 08:10 PM
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Backfiring, Smoking, Ready to Sell Car (just looking for ideas) Well I'm at a complete loss as to what might be wrong with my 98 Z28. Perhaps someone has an idea.
Over the winter I changed a few things. Prior to the project, I had a T-Rex camshaft with stock heads and everything seemed peachy. Well I decided I wanted to put some heads on it, and make it easier to tune by going to a 2000+ PCM. Here's what I changed:
Used CNC ported 853 heads with 918 springs slightly milled to 62CC (perhaps I have a bad spring)
2000 PCM out of a 2000 Trans-Am (repinned to work with my 98 Camaro, everything seems fine with it)
New MLS Gaskets
New LS7 lifters
New Comp 7.350 Pushrods
New TR55 spark plugs
New MSD plug wires
Flycutted Pistons
The result... constant backfiring and smoking. I don't have any misfire codes, but wow it sounds terrible. It WILL NOT run on it's own (ie Idle). My only codes are for the deleted AIR and EGR (but I have yet to change the codes on the PCM, so this is no surprise to me). I've checked the plugs and wires hundreds of times, and can't find anything wrong there... even went back to the stock wires just for ***** and giggles. I thought that maybe piston to valve clearance was in jeopardy, but after pulling the driver's side head, that doesn't seem to be the case.
Could I have bought a shitty set of heads? I had a valve job done on them and had them cleaned up before installing... only thing not checked were the valve springs... could one of them be bad? I'm at a complete loss... tired of throwing money at this thing. I have terrible luck with this car, and being in Utah there really aren't any shops that specialize in LSx stuff out here so I don't know what to do. If I can't figure it out, I'm selling it. I know someone else out there has way more know-how than I do and could figure it out.
Should I try a compression check? Just curious what steps I should take to try and diagnose this before selling it or "accidentally" starting it on fire. Thanks.
Over the winter I changed a few things. Prior to the project, I had a T-Rex camshaft with stock heads and everything seemed peachy. Well I decided I wanted to put some heads on it, and make it easier to tune by going to a 2000+ PCM. Here's what I changed:
Used CNC ported 853 heads with 918 springs slightly milled to 62CC (perhaps I have a bad spring)
2000 PCM out of a 2000 Trans-Am (repinned to work with my 98 Camaro, everything seems fine with it)
New MLS Gaskets
New LS7 lifters
New Comp 7.350 Pushrods
New TR55 spark plugs
New MSD plug wires
Flycutted Pistons
The result... constant backfiring and smoking. I don't have any misfire codes, but wow it sounds terrible. It WILL NOT run on it's own (ie Idle). My only codes are for the deleted AIR and EGR (but I have yet to change the codes on the PCM, so this is no surprise to me). I've checked the plugs and wires hundreds of times, and can't find anything wrong there... even went back to the stock wires just for ***** and giggles. I thought that maybe piston to valve clearance was in jeopardy, but after pulling the driver's side head, that doesn't seem to be the case.
Could I have bought a shitty set of heads? I had a valve job done on them and had them cleaned up before installing... only thing not checked were the valve springs... could one of them be bad? I'm at a complete loss... tired of throwing money at this thing. I have terrible luck with this car, and being in Utah there really aren't any shops that specialize in LSx stuff out here so I don't know what to do. If I can't figure it out, I'm selling it. I know someone else out there has way more know-how than I do and could figure it out.
Should I try a compression check? Just curious what steps I should take to try and diagnose this before selling it or "accidentally" starting it on fire. Thanks.
03-25-2009, 08:50 PM
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First of all, thank you for responding. I'll get a clip of the car running. No shops around here specialize in working on F-Bodies, so I'm kind of on my own here. I just don't know what it could be. I will get a clip of it as soon as I can. We're supposed to get snowed on, and with no garage I'm **** out of luck as far as working on it when the weather sucks. I'll do a compression check sometime this week (weather permitting) and post back the results. Thanks again.
03-25-2009, 08:57 PM
#4
When you put it together did you check the valve to piston clearance.With that cam and milled 5.3 heads you might of bent some valves if things were not checked properly.From the way you say it runs,sounds like a few bent valves.Have someone do a leakdown test of all eight cylinders.Or compression test.
03-25-2009, 09:16 PM
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When you put it together did you check the valve to piston clearance.With that cam and milled 5.3 heads you might of bent some valves if things were not checked properly.From the way you say it runs,sounds like a few bent valves.Have someone do a leakdown test of all eight cylinders.Or compression test.
03-25-2009, 09:21 PM
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Can we please keep this on topic? That problem is between me and you. I'm doing all I can to address that problem. I will PM you now. Sorry to everybody who now believes I'm a ******* thief.
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03-25-2009, 09:32 PM
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is it poping out the intake or exhaust? could be a number of things ignition timing, cam timing, bad cam or crank sensor, cracked spring, i'd do a compression check first, if it's good you could rules out bent valve or bad spring,
03-25-2009, 09:37 PM
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Much appreciation for the response! The POP is definitely coming from the exhaust. Would the PCM throw a code if the cam or crank sensor were bad? EFILive shows RPM when cranking it over so I know it's getting a signal from the crank sensor. Guess the next step will indeed be a compression/leakdown test. Thanks again for the response.
03-26-2009, 01:09 AM
#10
Did you get the coil signal wires right? Sounds like it is cross wired from that way you say it's backfiring and all. I would trace down each of those wires to make sure each injectory is firing on the right cylinder and that each coil is doing the same. I don't know if this has anything to do with it or not but if you look at a 98 LS1 tune you will notice that the firing order is moved 1 spot to the right from a 99-up tune. Again that may be something completely computer related but it could be something too. Just another thought for ya there.
Im also interested to see where you got your re-pinning information cause I'd like to do the same to my 98 T/A to take advantage of the extra tables and RTT.
Im also interested to see where you got your re-pinning information cause I'd like to do the same to my 98 T/A to take advantage of the extra tables and RTT.
