On my 94 LT1 with 104K miles. I developed an occasional miss a couple months ago. Over time, it has gotten worse to the point that now the car is almost undriveable. It constantly misses and feels as though it is "out of balance." It seems to shake with the speed of the engine rpm's. Almost as though one cylinders isn't firing and exhaust has become very rich smelling. It also seems to be almost backfiring through the exhaust, it's kind of a poping sound. It started hesitating a couple weeks ago during acceleration. It would shake up to 1500 rpm's then smooth out only to start shaking again with every shift. Now it has progressed to the point that you can't hardly accelerate or put the engine under any load at all without it shaking very badly.

I replaced the plugs and wires with AC Delco Wires and NGL TR55's which didnt help. I ohmed the coil and it was bad so I replaced that which also didnt help. After reading the threads here, I replaced the opti which also didn't at all.

I had a mechanic tell me that he thought that it could be the fuel injector drivers going bad in the ECM but didn't seem very confident about it.

Truth be told here, I am at a complete loss here. Due to loosing a great paying job recently and having to take a very low paying one, I really don't have much money to put into this. I am broke with every since of the word and don't know where to go next. The problem is that this is the only vehicle that I now own.

I am extremely desperate here. Any help that you guys can provide would be appreciated more than you know.

Sincere thanks in advance for any suggestions.

 

sounds to me you have a leaking injector or 2. get a fuel pressure gauge, take a pressure reading while running. it should be around 40psi. shut it off and watch the pressure. if it drops rapidly its usually an injector. On a LT1 you can also unbolt the rail and lift it out of the intake. turn on the key to pressurize it and see if they are leaking that way. Make sure you have the clips on the injectors that hold them to the rail, otherwise the injectors will shoot out of the rail.

 

......... Try pulling injector wiring clips off one at a time to isolate the lazy cylinder(s) ... remove injector plug and observe ANY changes in RPM ... you WANT the idle to drop ... if it doesn't change thats your weak cylinder ... then do a compression test to rule out mechanical issues ... i.e. valves , rings , head gasket , etc ...

 

excellent

 

Sorry gents. That is one thing that I did accidently omit. I pressure tested the fuel rails and it does not leak down. It runs aroind 42 pounds and when you turn the car off, after an hour, it has only fropper to 35 or so. I will try to find a compression tester and give that a go. Thanks.

 

If you can, a leakdown test will give you a better indication of where a problem might be coming from. Also, what did the plugs look like when they came out. Were they all dark? Oil fouled, wet? Could be the ignition module if you haven't changed that yet.

 

All of that doesn't tell you if the injectors are good or not. How many miles? Have you got rid of the usual culprits? Air leaks and filters?

 

The plugs were sooted black pretty badly. Seven of them were dry. The #7 cylinder was also black with a slight bit of wetness only on one side of the plug. They are gapped properly at .050" and were installed only 300 or so miles ago. By "leakdown test" are you talking about the fuel rails? If so, I did that and ran the rails up to full pressure which was 42 psi and after an hour of sitting with the key 'off' it had only dropped to 35 or so. At this time, I have not changed the ignition module. Is there a way to test it? I'm really gun-shy about continuing to throw parts at it if I can at all help it. I thought that I had read that if the module goes out, it won't run at all. Before this car, I have owned diesel trucks for years and have lost my touch with gas engines a bit.

 

A cylinder leakdown tester measures air pressure going into a cylinder through the spark plug hole compared with the air leaking out through the rings or valves. It isn't that expensive but requires the use of a compressor. The fact that your plugs are dry and sooty is good. They aren't oil fouled which would be an indicator of mechanical problems. Your issue seems to be either not enough spark, or too much fuel. Probably need to scan the engine parameters as the car is idleing to see what is going on. Could be your map sensor, but you're right, you don't want to throw parts at the car without knowing what the problem is. See if you can borrow a scantool. I know when ignition modules go out, weird things can happen, but don't buy a new one at this time. Go with a scanner.

 

http://www.carcraft.com/techarticles...ter/index.html

 

Wow. Sincere thanks on the feedback guys! My boss here gave me a number of a garage that owes him a favor. While I don't want to take advantage of the guy, I will definately ask him about borrowing or using his scanner at his shop.

In answering a few of your questions. The car has 104,000 miles. Filters are good. No vacuum leaks. I agree that just doing a fuel rail leakdown test won't show all injector failures. I ohmed them also and they are all even and within range. Again, I understand that it won't show all injector issues. Jon at FICINJECTORS said that if I send them to him, he will check them for me but my problem is that this is my daily driver for now and I can't be without the car for that long even though I really appreciate the offer.

If you unplug the injectors, each one will drop the rpm's. Here is a strange thing though. If you unhook an injector and hook up a noid light with the engine running, the niod light will not fire. If you start with the car not running and hook up the noid light and then star the car, it will flash as it is suppose to. If you then unhook the noid light and plug it back in, it will not relight.

Thanks for the leakdown test link.

 

Well, it seems that I had some problems with my new plug wires. I pulled them off at the ends to ohm them. When I reinstalled them and then ran the car, it ran perfectly. I am unsure whether they were not in the correct location or if one or more were not fully plugged in. Thank you all for your help and God Bless.

 

I can't be sure but you might have a bad wire. When you yanked them out, you might have "fixed" it. Can you cut the ends and reapply new ends?

 

I am unable to put on new ends but if the problem arrises again, I will definately replace them again. I used the AC Delco wires because it is what I could afford at that time which was only about 300 miles ago. Next time I think I will go with the MSD wires. Thanks aklim

 

MSD sells ends and you can buy those and if you have their tool, it is SO MUCH easier to install. You can either buy the tool or pay me shipping both ways and I can lend it to you.

 

Great! If it acts up again anytime soon, I am going to suspect the wires even though they are new. Thanks again.

 

Glad to hear you got it running without sinking anymore money into it.

 

Me too LT1!