Well been a couple months since I've worked on my junk. Finally got back to it and still fighting with this Backfiring issue. Here's the situation- at idle engine runs great no backfires, no problem going through the entire rpm range, will idle all day with no issues. Once putting the motor under load (regular driving) it starts to backfire. No idea why it's doing this. Driving style doesn't cause it at all. Just happens. Temperature change doesn't cause anything, just backfires when it wants to. Now when it does backfire it goes through the exhaust. Once it starts to backfire motor seems like it wants to quit and it starts jerking from the backfires. While jerking the SES light flashes (thinking it's cause the motor isn't really running). To date I have replaced everything in the ignition system to include distributor, cap, coil, module, plugs, wires, ESC, wiring harness, Pressure regulator, fuel filter, and fuel line from the tank up. Timing is at 6 deg with the connector unhooked. I have no SES code otherwise to lead me in any direction. I have also checked the TPS and it's functioning properly and is sitting at .6 for idle. Comeon Gurus I need some help here before I drive it off a cliff (if it will make it that far).
BOB

 

How many miles on it? Camshaft going bad? Valve hanging up? Bad valve spring?

 

Pickup coil would be my guess.

SES flashing during cutout usually means the ECM isn't getting distributor pulses.

 

Did the new distributer come with a pick-up in it? I would have thought so. My general experience with a gm pick-up coil is that its either good or its bad. No good days or bad days so to speak. If its bad, the car doesn't fire. Can we get some more info. Is the pick-up coil new with the dist. or did the old one go into the new distributer. I would think a bad pick-up coil would cause a no fire misfire. I'm thinking a mechanical issue is allow it to fire (back fire) in the exhaust. Try pulling plug wires and see when if the backfire goes away. If you pull all 8 and still have it then that rules out my theory. If you pull one and the backfire goes away you have your cylinder. The car will obviously run like sh-t on 7 cylinders but it should be enough to track down a bad cylinder.

 

Distributor came with a new pickup and has a lifetime warranty. Cam has 1500 miles on along with the rest of the bottom end. The heads where the only item not rebuilt as they only had 60k miles on them, and everything looked good. If I had a bad valve spring or something wrong with a cylinder then wouldn't it act up at idle as well? The Idle is fine, only happens when a load is put on the motor.
Bob

 

Bob
Did you have this problem before changing to the new plugs? Sounds like a bad plug or wire under load. I'm wondering if this problem was there before the "complete ignition overhall". A crack in the porceline or to much resistance in the plug wire could cause this.

 

been running the same platinums since I first cranked the motor. I have changed out plug wires a couple times though. Might just have to swap them out again and see if that changed anything.
BOB

 

Have to reitterate one thing here...

If the SES is lighting up to the "miss"...you can eliminate everything past the dizzy...nothing tells the SES to light with a bad plug/wire/etc...just disconnect a wire off the plug and see.....gotta be in the dizzy or further back, IMHO....assuming it's not somehting that is setting a code.

 

Did you have this problem pre "new distributer"? Was that the reason for changing it? Further back would leave only the spark module and 'puter wouldn't it? All items you have already changed? You mentioned a life time warranty on the dizzy. Have you thought of getting another? Or was the problem there pre "new dizzy". Tough one!

 

Do you know anyone with a good quality scanner (ie snap-on etc) that you can hook up and go for a ride. This way you can re create the problem and see what the ses light is coming on for! Might be a way to save pulling ALL your hair out!

 

dont know anyone with a decent scanner. Called around to all the local shops and no shops I can find Have one either. Had problems like this before, so thats why I've swapped out so many of the ignition components. Thing is everytime I've swapped something out it's gotten better. Then it gets worse again. Last item I can really swap out that deals with timing is the Computer. Just wish I had a good scanner or datalogger to point me in a direction on what could be wrong. I think I'm on my 3rd distributor, so I can pretty much say that is definatly not the ditributor.
Bob

 

I'm not telling you what to do here, but, I run my own Midas Muffler shop here in Windsor and we have all pretty much gone to full service shops. Maybe you could contact one of they're shops down there and see if you could get a scan there. Ask what kind of scanner they have and if it has real time capabilities. There has to be some shops in your area that will scan it and go for a ride with you. They may want a chunk o change since they know that your going to fix it yourself, but sometimes you find a shop that is reasonable. Try some of the speed shops down there or a place that does performance tuning.
I'm thinking that by now it would be cheaper to pay for a scan then to keep replacing parts. This has to be getting frustrating! Good luck!
Rob

 

well for S&Gs swapped out the wire going from the Coil to the distributor but no change. Almost seems like spark is being totally cut from the motor, then suddenly it kicks back in causing a back fire. So question is what would cvause it to toally loose spark then regain it milli seconds later? COmputer is the last thing I can think of anyone else care to chime in?
BOB

 

Is it a tpi motor? If so maybe check resistance on your injectors, may be a long shot but its an easy test. Just thought id throw it out there.

 

Check all your grounds. From your last post it sounds as if your loosing power (or ground) to either the ignition or 'puter. As you start to load the engine the resistance in the bad circuit may be causing a loss of power. Just another $.02 thought. You should be around $18.00 now!

 

Yep Tuned Port 327 in a 94 4x4 Toyota pickup. Going to double check and probably redo all the grounds tomorrow.
How can I check resistance on the injectors?
Bob