ESTAVER Posted March 21, 2009 Share Posted March 21, 2009 Having increasing problem with stumble/backfire when accelerating in O/D. All other gears have excellent throttle response throughout all speed ranges. This started as stumble on light excell. uphill and has progressed to heavy stumble and serious backfire at accell. at any speed/grade in O/D. Tranny downshifts fine when called for, but now I don't dare punch it in O/D for fear of bolwing the air filter box apart (again) Normal cruise in O/D is smooth. Have 190K on engine with original injectors, but I would think injectors would show at other gear curves. The only other performance problem is a little idle hiccup now and then. I have not pulled the O2 sensor yet, but the readouts on diagnosics display appear to be in the indicated range. I've checked most of the Shop Manual looks, but I'm hoping to save time in the troubleshooting process by hearing y'alls suggestions. Thanks as always...Drew in Charleston,SC Link to comment Share on other sites More sharing options...
DAVES89 Posted March 21, 2009 Share Posted March 21, 2009 If you havn't done so do the coil pack/ignition control module upgrade and clean the Idle Air Control. Link to comment Share on other sites More sharing options...
D-a-n-i-e-l Posted March 21, 2009 Share Posted March 21, 2009 Sounds a bit like the TCC is acting up. Link to comment Share on other sites More sharing options...
Jim Posted March 21, 2009 Share Posted March 21, 2009 I know it sounds simplistic but try new spark plugs.See if it stumbles/backfires when the engine is relatively cold, before the temp reaches 140 degrees. That is when the system goes into closed loop.My first Reatta had a similar problem and after much checking I finally replaced the plugs and everything was fine. The plugs "looked" perfect but wouldn't work when the car went into closed loop. I put the old Reatta plugs in a Corsica and it ran fine since it was not as computer controlled as the Reatta. Link to comment Share on other sites More sharing options...
Guest crazytrain2 Posted March 22, 2009 Share Posted March 22, 2009 While you're at it check the plug wires (how old are they?)and the mass airflow sensor (tap on it lightly w/engine running *NOT on the flat plastic surface area though*). Link to comment Share on other sites More sharing options...
padgett Posted March 22, 2009 Share Posted March 22, 2009 Secondary ignition will act exactly that way (stumble at moderate load/low rpm). It also will rarely set any codes. Does it smooth out if it downshifts ?If so my experience is above 45 mph (sounds like you), check the coilpack for proper resistances (see FSM)first - below 45 mph replace the plug wires/plugs. Link to comment Share on other sites More sharing options...
ESTAVER Posted March 22, 2009 Author Share Posted March 22, 2009 Thanks for the help gentlemen. I'm going to apply your suggestions today and will report progress. Link to comment Share on other sites More sharing options...
Guest tomt Posted March 22, 2009 Share Posted March 22, 2009 My similar problem ended up being wires, but more importantly NEW wires. I'm guessing some of them have been on the shelves so long that there may have been moisture issues. The wires tested bad, were replaced, and the stumbling was gone.Again, a freeby as the wires had been sold to me by a Buick Dealer, and were tested and replaced by another one.Incidentally the stumble only showed up as it went into overdrive, as yours.Tom T. Link to comment Share on other sites More sharing options...
ESTAVER Posted December 24, 2009 Author Share Posted December 24, 2009 Again, thanks to all forum members for your advice on this problem.I looked at all the suggested sources of this stumble but found no problems. Recently I decided to go with the Delco coil and module upgrade the Padgett the Man has created as an instructional. (great) In that piece mention was made about looking at using .045 gap on the plugs instead of the factory .060 setting.Low and behold... stumble is now history. Throttle response is again immediate and clean in Overdrive, on uphill or the flat.I had prepared to pull out my last two good hairs trying to fix this problem. Now I can do that comb over as planned.Thanks to Padgett for taking the time to create his many helpful postings and tips. Drew in Charleston, SC Link to comment Share on other sites More sharing options...
charlie1 Posted December 25, 2009 Share Posted December 25, 2009 Thanks for posting the resolution. Link to comment Share on other sites More sharing options...
padgett Posted December 25, 2009 Share Posted December 25, 2009 Unfortunately this means that you have a weak ignition system and the fix may be temporary. Closing the gap reduces the load on the ignition system. The level of misfire you mentioned is excessive even for a Magnavox. (original is not that bad a system, just the Delco is better, a bolt on, and a good used one is less expensive than just a module or coilpack for a Magnavox). Link to comment Share on other sites More sharing options...
ESTAVER Posted December 25, 2009 Author Share Posted December 25, 2009 Thought I should mention that after finding the .045 plug gap worked as a fix to this problem, I did not replace my Motorola Coil Pack as it appears to be performing fine. Link to comment Share on other sites More sharing options...
ESTAVER Posted December 25, 2009 Author Share Posted December 25, 2009 Thought I'd also mention that after the .045 plug gap cleared the problem, I didn't change my coil and module to the Delco.I just saw a note from Padgett that this may be a temp. fix.If I can round up a Delco package at my local yard, I think I'll go ahead and make the change just to ensure peak performance. Link to comment Share on other sites More sharing options...
Guest ekvh Posted December 25, 2009 Share Posted December 25, 2009 I believe my plugs had to be set at .045 to run decently, that was after the Padgett upgrade with the delco coils. Maybe the one I installed is weak. I checked resistances and they were uniform across the three coils. I have an extra set in the trunk, perhaps, when it gets warmer, a LOT warmer, I'll switch them and go back to .060 gap. The other item in this mix is the inferior plug wires available. They don't seem to last a year. My supplier gives me new ones, but I would sure like to find a good brand that would last. Link to comment Share on other sites More sharing options...
padgett Posted December 26, 2009 Share Posted December 26, 2009 Plug wires I put on the Blue car two years ago (Bosch 8mm from AZ) seem to be working fine. Should have enough AC Rapidfires to last a while. #3 is gapped .045 and #14 .060 - seem to be the same plug otherwise. Link to comment Share on other sites More sharing options...
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