[xgoater]

HELP PLEASE!

I have a 1996 Tahoe 2 door 4WD with the 5.7L gas engine. The "service engine soon " light came on a while back. It starts right up. Idle is rough when cold. Smoothes out mostly at higer RPM but not totally. Both seem a little better when up to operating temperature. Lately it is a lot rougher at idle and a little roughness at higher RPM.

Code says a misfire on cylinder 5. I put new plugs, wires, cap, and rotor on. No difference. I have run Lucas fuel treatment through it for about 200 miles thinking it was a sticky injector. No change. Pulled the coil and had it checked out - they said it was okay. I looked at vacuum lines and nothing appeared to be cracked or loose. I've tried to read the service manual but IMP that is the second poorest written book I've ever read.

I need to go to KC this weekend (375 miles one way). I'm afraid to drive it. I'm not a mechanic, I've done what I think I can, and I don't have the money to take it to a shop or throw parts at it.

Can anyone help me with what might be wrong with it?

Thanks in advance for any assistance!

Terry

[RichV]

Terry, Sounds like you hit all the basics. I have run across this same problem twice in the past few years ( I'm a 25 yr tech).Both vehicles showed misfire codes that didn't go away even after full tune and motor -vac (high end injector/top half cleaner). The trucks ran fine if you drove them normally but as soon as you stomped on it to pass or climb up a hill misfire galore. If these symptoms sound like yours,pull the drivers side valve cover and adjust the valves. It's pumping up the lifters and holding the valves open. Are any other cylinders showing missfire or just 5?

[sleepy]

Start it and unplug the injector on no5 if it doesn't have an effect you could have a bad injector OR broken or rubbed threw and grounding out wire to that injector. or maybe a bad connection (corroded plug)

[Larry P]

Terry can you post a little more info, do you know what the compression is and the leak down on cylinder 5, you need to know if the cylinder is good before replacing everything around it. Also need to know fuel pressure and if it leaks down or not after shutting the truck off.

[stimpy]

these are known for injector problems at 75+ miles replace the injector . its cheaper to buy a set theu rock auto as morethan likey your going to loose the other ones , the pintle seat wears out in them

[xgoater]

Thanks for the help guys!

Rich - No, it's just a rough idle. The higher the RPM, the smoother it is.

Sleepy - I'll look at checking that. I'm not a mechanic so some of this "simple" stuff confuses me. But I got the service manuals for it so I'll give it a try.

Larry - No, I haven't done any compression or fuel pressure tests. That was going to be my next step, but I don't have any test equipment. I went to AutoZone to rent theirs and the guy there said I shouldn't try it by myself if I'm not experienced in doing it!!???

Stimpy- That;s exactly what the high school buddy mechanic said.

I went back to my buddy mechanic and he said again it's a plugged fuel injector. I just need to replace the injector and it will be back to normal. The only problem is that year has the "spider" injector and you can't replace just one - you have to replace them all - which isn't a bad idea. But the set if $400+ at Rock and I don't know if I have the expertise to be able to figure out how to R&I the injector set.

He said it won't hurt anything to drive it - in fact he said a trip like that could help free up the injector with the Lucas treatment in it. So I'm leaving for KC in the morning and we'll see how it goes.

Thanks again everybody! KC or bust!

[xgoater]

FWIW, I just got my Tahoe back from the shop. My misfire problem ended up being a leaking intake gasket! I was lucky (???) enough to get a retired GM mechanic to look at it and in less than 5 minutes he diagnosed it as a leaking intake gasket. He referred me to a local shop who confirmed the diagnosis and then fixed it. She runs like a champ again.

I know there can be a lot of causes for a problem like this but I thought I'd post this so someone else doesn't throw parts a problem that may not be the real cause. Fuel injectors, sensors, coils, etc. can add up to big bucks real quick and still not even touch the real problem. So if you're not sure what your problem is, try and get a good mechanic to diagnose the problem. It will save a lot of time and money in the long run.

Thanks again for all the help!

Terry

[Coupe62]

Mine did the same thing and it turned out to be the coil

[xgoater]

Sounds like you got by about $500 cheaper than I did! I was hoping mine was going to be simpler and cheaper than an intake gasket, but no such luck this time. But this is the first major repair I have had to do to it in 13 years, so I suppose it was my time.

These newer vehicles run and perform great with all the computers and stuff on them but when they go bad it can be a nightmare to figure out. At least for me it was.