Misfire, Can't find cause.

[chadm_88]

My buddy's neon has a misfire on Cyl. 3 and I can't figure out what's wrong. We've replaced the spark plugs, checked compression, and checked spark from the wire. Should I proceed to check fuel injector pulse, or are there any common problems with neons and misfiring?

Also, all the cylinders checked out at around 175 PSI, which is good because they were even, but what is the spec supposed to be for these?

[mikeburrit01]

ive had the same exact problem, i know you posted this a while back, but ive just given up, im convinced that it's either the valve spring on the intake side, the cam, or the pcm... either way, i might keep the car just as a mpg saver or look for a salvage complete head that wasnt totaled due to broken timing belt

[Johnobub]

I had the misfire problem, I tried everything. During the time of having the misfire problem, I also had a problem with the head gasket and needed a rebuilt head because the original head was warped so bad. A new cam came with the rebuilt head and after replacing the head, no more misfire. It works fine now. This proves it is probably the worn cam that caused the misfire problem.

[mikeburrit01]

where did you get your rebuild head? did you get a good price? im in fear of having to do this because just doing the head gasket and re-timing the thing was such a hemorrhoid.

[Johnobub]

Originally Posted by mikeburrit01

where did you get your rebuild head? did you get a good price? im in fear of having to do this because just doing the head gasket and re-timing the thing was such a hemorrhoid.

It cost around $800. I figured it's cheaper than buying another car so I fixed it. It's still running good. No more misfire error.

[mikeburrit01]

alright, thanks johnobub, i think even 500 more is more than im willing to put into this car. id rather just save for a newer

[Oldsmobile Doctor]

I have replaced the coils on all three of my Neons two misfired and one hesitated

[danielsatur]

Don't rule out the injector, because a clicking sound and pluse doesn't mean the flow rate is correct.
Try rolling injector 3 with another to see if the problem rolls, if the injector is bad a local diesel shop can micro bath, blow out, test flow rate, and put a new seal on it.

[mikeburrit01]

ive done everything.... it's mechanical. and i know what you're thinking, did you try...? yes i did, the only electrical thing i didnt swap was the computer.

anyways, i am thinking of going to the salvage yard and getting a head off a totaled sohc neon just for the camshaft. but my main concern is that majority of totaled neons occur from timing belt break and the valves being smashed. would this affect the camshaft lobes or twist it?

[danielsatur]

If the compression test is good, the head, valves, and cam are good.

[denisond3]

I have a 97 Neon SOHC, that has a bad misfire, which the codes tell me is either "CPS signal not present when engine cranking", or "random misfire". I have replaced the usual stuff; plugs, wires, coil pack, Crank Position Sensor, Cam Position Sensor, etc.
I have had a mechanic (a neighbor) tell me the 1st generation Neon camshafts arent held from moving left-right as closely as most cars, and when the cam shifts toward the timing belt end of the engine, the target magnet in the end of the cam moves away from the cam position sensor too far - like .010" or more. Then the engine misfires because it wont run right without the cam position signal. He said a new cam position sensor wont fix it, but a new target magnet (it screws into the end of the cam) would help.
I have other hobby cars, and havent gotten around to looking into this yet. I also know the engine wiring harness on my Neon has some problems. It was damaged by heat and I had to replace about a dozen of the wires in it, but may have not used the right wire gauge and splice locations. When use an oscilloscope to look at the signal going into the PCM, there seems to be more noise than signal. In fact the signal seems to disappear in the background noise - though this could also be the fault of my 'uncompensated' scope probe. I want to fix the car, but before I begin, am hoping to find someone who can get me a good engine wiring harness. I have found many 1st generation Neons in junkyards, but most of them are either missing the engine (which the wiring harness mounts to), or at least that wiring harness.

If anyone happens on a solution, I hope you will tell us about it.

[XWrench3]

i have had misfires before with mine that gave me fits. if there is more than 60,000 miles on the wires, replace them. that is what fixed it every time. the codes indicated the second time that it had a bad t.p.s., but it was WRONG to the tune of $130,00. a $30.00 set of wires fixed the problem.