Why does it Misfire after new Plugs & power brake booster

Asked by Oct 01, 2010 at 09:17 PM about the 1990 Chevrolet Lumina Minivan

Question type: Maintenance & Repair

1990 Chevrolet Lumina Base 6 Cyl 3.1L  (88,000 miles)

June 3, New spark Plugs installed.  (Original Spark Plug wires remain)
July 15, Power Brake Booster Replaced. Shop said battery was disconnected and computer needed to automatically reboot. But the engine stalled all day at stops and when coasting.
July 19, Shop ‘cleaned’ idle control valve and stalling problem stops. But the Engine now misfires.
August 9, Shop tests (and dislocates coolant reservoir, now rubber bushings are cracked/split) and decides #5 is misfire but they are not responsible.

When the engine is cool, it runs steady but as engine heats up, misfire starts.

Shop # 2 says New Spark Plug wires must be installed and Induction Service required.

5 Answers

165

i would put wires on it. also chevy 3.1 and 3.4 are very prone to valve issues. if the engine is noisy i would have valves checked. but the wires are a more likely cause of your misfire

I am getting into this way to late to help JWN, but for anyone else with a misfire on one cylinder...pull the plug wire off the offending cylinder and exchange it with one of similar length on a cylinder that is firing properly. If the miss moves with the wire, you've found the problem. If not, you have a different problem. Check for spark at the plug by sticking a philips screw driver into the end of the plug wire for the offending cylinder (get one with a well insulated grip and be sure NOT to touch the bare shaft), hold it near a grounded metal portion of the engine, have someone crank the engine while you watch for spark. NO spark..you have a coil or ignition module problem. If there IS spark you have a spark plug, valve, head, piston or ring problem and need to progress to a compression test and test the plug to narrow the possibilities. Again, to test the plug switch it with one that is working. If the problem moves with the plug, it is the problem.

misfire can be caused by bad wires and coil pack. in this case it sounds like the coil or ignition module

265

bad injector on that same cyl was my fix...juss sayin.. along with the other options..good luck

If you suspect a bad injector, do the same as the plug, exchange it with one in a cylinder that is firing and if the problem moves to that cylinder you have found the problem, that injector. I do not like replacing parts to "find out" if that is the bad component. With a multi-cylinder engine of any kind, if the component is interchangeable without major work, trying that will tell you if it is that component. It can be time consuming but pin points the problem or totally eliminates something that could be contributing...I like a for sure answer that the component I suspected IS or IS NOT the culprit. If not I can go on to something else. You are right though, it could very well be an injector. A lot of times a sticky injector will come back to life, at least for a while if your run injector cleaner in your gas. Another fix is MotorCote in the gasoline (or diesel fuel); about 4 oz will usually free up a sticky injector. The recommended amount in the oil will usually free up a sticking ring. Actually, I would recommend both. My son has used MotorCote to get chain saws and two stroke motor cycles to run after they had already seized up one or more times. It works wonders. n He owns a repair shop and works on a lot of motorcycles, ATVs, snowmobiles and lawn mowers and swears by it.

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