Evening everyone. I have a 1989 Iroc with the L98 350 in it. The motor was professionally rebuilt to stock about 2 years ago right before I bought it. The car has always fired immediately and ran perfect. Last weekend I changed the oil and the following morning picked up what sounded like a valve tap. Two days later I went to turn a corner and it started backfiring out the exhaust and back through the intake. I was able to nurse it home at about 40 with a consistant backfire/popping. The car still fires and idles well (other than the tap), but the second you start to give it any gas, it begins backfiring. The more gas the worse the backfire. Im no mechanic, but can usually fix it if I can figure out what it is. Thats where Im looking for help. Can anyone put in your thoughts and ways that I can check it. With no garage and no money right this second, wouldnt you know that is when it would happen!

Update: This story was posted earlier on another site. I since found where the steering column was rubbing on a spark plug wire and had wore it literally in half. I run down to AutoZone with a big smile expecting a cheap fix. I unplug the wire and it actually runs well considering. I get the new wire and plug it in. Right back to the same thing. Its a tick with the wire off and a backfire through the intake with it plugged in. Much worse issue plugged in than without. Any help would be greatly appreciated.

Thanks in advance
Bob

 

The wire being bad may not have been firing the spark plug. Pull that plug, it may be gas fouled. If so replace it. Check that first. Also, you may have a vacumn leak. Check all vacumn lines for cracks, tears, or off fittings. Also, if I am getting this correctly, you have a tapping sound where? Intake, valve cover area?

 

Thanks Badman for helping out. Sorry if I wasnt clear at first. I was trying to get the message out before dinner. I really need this car back on the road. The noise (without the plug wire on) seems to almost be an external spark tap, ting, peck. Once the plug wire is back on, its a definite pop as if it was a backfire in the intake. The pop in a hollow area. The peck is very timely and consistant. The pop does not seem to be as repetitious. It runs well without the wire, but obviously like on 7 cylinders. With the wire hooked up, it stumbles and falls all over itself. Cant hardly drive it down the street. The plug is firing well and is not fauled.

 

Might be a bent pushrod or a lifter collapse or a broken rocker arm on that cylinder. Only way to know is pull valve cover. Also check dist. cap, terminal might be shorted out, but it sounds like it is getting spark to that cylinder. Also check spark plugs wires are on correctly as to firing order. 1-8-4-3-6-5-7-2. Trying to think of anything else, if I do I will post it.

 

I'm thinking that when the spark plug wire was shorted out due to the column rub, you may have caused some sort of short or maybe fried something. I would post this question in the electronics section also. Just a shot in the dark, I'm out of ideas and guessing now. Maybe some of the TPI gurus can chime in.

 

Ok, thanks for the help. Now I have to admit that I should have just done this 6 months ago when it happened. Ive been sitting around worried to find out it was a thousand dollar fix and it was a rocker nut that had come off. Screwed it back on, checked the others and it runs perfect again. Now its time to start looking at this board and see what you guys can point out for boosting the performance without having to dig in to the block. Ok, well unless you can walk me through a cam. Id love for it to have a little cam sound! Many thanks.

 

Glad I was able to help. You might check the other nuts, sometimes they lose their tension and need to be replaced. Or go to a locking set of rocker nuts. That will cure any further potential problems. Badman

 

Cam swap? GREAT mod, but not sure it should be the first. If I ever buy another L98 and mod it one thing at a time, it'd be headers/exhaust first, torque converter second. ....but the cam swap taught me SO much. It was a great experience for this "non" mechanic!!!

...BTW, glad you got the problem solved!