Alright guys, need a few words of wisdom on this one. I have a 94 Z28, with a fresh 4 bolt main short block, just installed, with LE1 heads/cam and full bolt-ons and tune. These were on the car before the new short block, so everything should be good. Well I went to start the car and it wouldn't start, only pop and that was about it. Checked the fuses and one of the under hood fuses for my injectors was blown, #9. Tracked it down and turns out I had pinched two wires under my fuel rails and they were shorting to the intake. So, because of their location, I just used some new wire and a few but connectors. Car fired right up, but now has a backfire out the exhaust. Weird thing is, it will run okay for 15 seconds or so, then pop once then run fine for another 15sec. If I step on the car it will rev right up without a miss or anything... Also the backfire is not harsh or loud, more of a pop. So pretty much the fuel is just burning late. Well, I used PCM Communicator to scan the car and when it is idling and starts to miss/backfire it shows "injector fault". If I rev it up from 2K-3K, and keep varying the RPM it goes to "no injector fault". So I am thinking that either I have another frayed wire I can't see, or maybe my connections are delaying the signal, causing the injectors to fire late and puts the fuel after the compression stroke. I will try and solder/shrink wrap the connections in the next day or two, it's just really hard to get to :-( and it's 30* or so up here... Is there anyway to track down which injector is triggering the injector fault? And do you guys agree with me that it is most likely a wire going to my injectors?

Thanks for reading,
Bill

 

its possible that it ruined the injector driver in the pcm

 

I would try fixing the wire again corectly and make sure you did not connect them backwards. Then check all of your wiring again to make sure everthing is as it should be. It would not cause a injector fault to show up but are you sure you dont have a exhaust valve lashed a little too tight?

 

Injector driver in the PCM? Sounds like a specific circuit and I would probably need a new PCM? Great anyway to test that. Doughboy, I know I spliced the right ones together, but I will re-do them with solder and I thought about the exhaust valve until I saw the injector fault code... Does anyone know how to further diagnose and injector fault, like track down which injector or how the computer knows there is an injector fault? And does anyone have more info on the injector drivers in the PCM?

Thanks,
Bill

 

Which injector fuse was blown? Fuse #9 controls injectors 2, 3, 5 and 8, while fuse #10 controls 1, 4, 6 and 7.

 

It was the #9 fuse and the two wires that were shorted to the intake were on the even side of the motor, and there were two wires shorted, injector 2 and 8 . My other questions is why does the "injector fault" go away if I keep the rpms up and varied so the car does not miss?

Thanks,
bill

 

Easyist way I know of to check for a injector fault is to first measure the resistance of the injectors with a DVOM all should be close to the same whitin a few ohms. Then Hook a noid light up to each injector harness 1 at a time and see if it flashes when the car is running. If it does not flash at idle but flashes when you rev it up I would say you most likely have a pcm problem due to the shorted wires. Then there is a special injector test tool you can buy from most major tool companies and some autozone type places that can be used to pulse the injector. Basicly it hooks to 12 volt battery then connects to the injector and has 2 buttons one pulses the injector 1 time the other pulses the injector a bunch of times. Hook the tool up to the first injector then turn the key to the run position to build fuel pressure (you will need to have a fuel pressure guage hooked up) push the button for 1 pulse and the guage should at least move a small amount and you should hear the injector fire (clicking noise), If it does fire write down how much drop in pressure you had then cycle the key again to raise the pressue back up and push the button to pulse the injector multiple times, again write down your results. You need to do this on each cylinder much in the same manner as doing a compression test, when you are done if you see a major difference between 1 or more cylinders recheck the cylinders with bad readings again and if your readings are not right that is a good place to start replacing injectors. After you do this test you need to take all the plugs out and disable the ign system and spin the engine over a few times with the starter to clear all of the raw fuel out of the engine. If you dont there is some possibility that the raw fuel will build up in one cylinder and hydraulically lock it and causing damage when you try to start the car. Some of the higher priced tools alow you to hook up to the injector harness and do some testing on them as well but to do just one car it would not be worth the price of one as it would be much cheaper to find a shop that has one and have them do it for you. This is how we do it in the shop when we have a lean cylinder or a missing cylinder that is not ignition or compression related. In your case I would do a compression test first to make sure you dont have a valve hanging open as the engine was just rebuilt and lashing a valve too tight is not uncommon thing to see happen. I know a tight valve will not cause a igjector fault to show up but it will cause a backfire. Good luck I hope you get it figured out. Let me know if you find anything else out I am always willing to try and help
Take care
Rob

 

so do u know how the car will act if the exhaust valve lashed to tight? and can it get tightened by it self some how?

 

If its lashed too tight the exhaust valve will be held open all the time and will backfire out of the exhaust when the cylinder fires. If it is just holding it open a few thou. the backfireing may get better or worse after the engine starts to get some heat in it. Other than pulling the valve covers and readjusting all the valves there is no way to be 100 percent postive. You can do a compression test which should show a low reading on the cylinders with lash too tight. There are other things that can cause a valve to hang open or stick open like valve guides too tight or if the piston to valve clearance was not correct and on initial startup and the piston kissed the valve or if you are running alot of seat pressure and a really lean mixture it can tulip a valve real quick in some cases. Dont really know too much about your engine and what was done so it tuff to tell. I would run a compression test first to make sure you dont have more than one problem (ie pinched wire and a tight valve) that way you can at least the tight valve lash out. Then move on to the next possible problem untill you find the one that fixes it.

As far as tightening on its own I would not think so usually if the adjusting nut or poly lock is bad they will loosen not tighten. but what can happen is when you are adjusting them if you turn them down too far or bottom the lifter by accident even if you loosen it up all the way the plunger in the lifter does not come back up right away so if you try to readjust with out spinning the engine over to make oil pressure push the plunger back up you will get it too tight even though it may seem adjusted right. Then when you do start it and oil pressure pushes the plunger up in the lifter the lash is way too tight and holds the valve open.

 

Yeah, so one of my connections must have been bad. I took the time to lay there on my motor and solder everything together. Got rid of the injector fault, but the pop is still there. I'm assuming that it is an exhaust valve with a little too much pre-load, I will have to check that out next weekend or whenever.

Thanks for the help and I will report back in a little while

Bill

 

hmm this kinda seem what might have happened to mine..when my car warms up its starts missing and hesitating hella bad and it just keeps getting worse and worse...

 

alls i have is bolt ons...new opti/wires/pluggs/coil/o2s..car runs perfect when its cold getts a little warmer and it just messes up unless iam punching the gas....

 

I had that "injector fault" message as well. It was a constant ground on my #8 injector. When you would turn the key to the "on" position it would ground the injector and the injector would be wide open dumping gas into the cylinder...even before starting the engine.

I went through the wiring harness and it went away.
Check your wiring if you -all of it- if you have not already.