redtailed

I've been trying to help my friend repair his 1990 Suburban V8 but I am having some trouble narrowing down the cause of the problem. Any help would be greatly appreciated.

It is a 1990 Suburban 1500 V-8, with throttle body fuel injection and automatic transmission. When started, engine will start smoothly and idle for one revolution, then stumble, surge and die. If throttle is pressed down, engine will stay lit, but will miss severely and backfire to the point of not being in anyway drivable.

So far I have checked the spark plugs, and the #7 cylinder (passenger side, nearest to firewall) was soaked with unburnt fuel. Distributor cap was checked and the rotor contact showed wear, and the points on inside of cap showed heavy build up of carbon. Both were replaced but Problem has not gotten better.

Pulling different spark plug wires results in a very noticeable miss for that cylinder, including when pulling the wire for the #7 cylinder. This seems to suggest the #7 cylinder is indeed firing.

The ECU shows no trouble codes whatsoever.

Has anyone had any similar problems or suggestions on where to look next?

maxxman04

run compression check on all cylinders. should be 150 or better with no more than 10 psi difference between the highest and lowest cylinder. burnvalve, cracked head/block, worn rings, all will cause low compressoin, no fire, bad idle and such.

73shark

Welcome to the forum.

Be sure to have the throttle wide open when doing the comp. check.

maxxman04

yeah, i did forget to mention that. my bad. thanks 73shark.

VanGo

Maybe you should swap the #7 plug with another cylinder and see if the problem follows the plug.