johnj92131 Posted August 21, 2016 Share Posted August 21, 2016 Replaced the exhaust manifold with new Amazon manifold, a new oxygen sensor, rebuilt Neon "703" injectors and a new CPS last weekend. When I got the truck back from the shop, I noticed some light throttle backfiring/poping going up a hill. At first, I put it of to the ECU relearning because of the fresh injectors. So I made a point of driving the truck most of last week to give the ECU time to relearn. By this Saturday, nothing has changed. So "assume" something is wrong with the timing or I have some faulty "703" injectors. So far, no check engine light. The old exhaust manifold was patched up to pass the last smog test in March. By my July cross country trip, I was sometimes getting a check engine light with a lean condition error message. But most of the trip, the truck ran just great. Now with all the new parts, I expected the truck to run great all the time. Backfire/Popping goes away with a heavier foot on the throttle, then comes right back under light throttle load conditions. Also some occasional "missing" at idle. Any Thoughts? I did read gogmorgo's thread with his bad fuel pump here: http://comancheclub.com/topic/50995-loosing-power-under-throttle/ But have not checked performance on a long mountain climb, just a short steep hill on the way home. Maybe I should take an hour ride up to Sunrise Highway (sea level to 4000 ft) and report back? I am leaving Wednesday to pickup the 86 diesel MJ in Victoria, B.C. then deliver the truck to Michigan. So would like to fix the problem by Tuesday. Link to comment Share on other sites More sharing options...
64 Cheyenne Posted August 21, 2016 Share Posted August 21, 2016 If this was me, I wouldn't go in the MJ if if this issue wasn't resolved. As far as helping, I'd check fuel pressure, maybe put the old injectors back in, see if that helps. And look at the plugs... FWIW the only time I had issues like this were from contaminated fuel, couple cans of HEET later all was better, and I'm not a fan of HEET because of alcohol base, prefer to keep tank full to prevent condensation. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 21, 2016 Share Posted August 21, 2016 No CEL, but did you check for fault codes with the key? Link to comment Share on other sites More sharing options...
johnj92131 Posted August 21, 2016 Author Share Posted August 21, 2016 No CEL, but did you check for fault codes with the key?No. Will do that ASAP. Also looked at old injector Saturday, o rings are damage or missing now. Link to comment Share on other sites More sharing options...
johnj92131 Posted August 21, 2016 Author Share Posted August 21, 2016 Blink codes are clear. Only 1-2 Battery disconnected and 5-5 End of Codes. Battery was disconnected to replace starter motor also last weekend. Gas tank is full. So I am off for a drive up the I-8 freeway to the first 4100 ft pass at Sunrise Highway. Then we will check the blink codes again. Link to comment Share on other sites More sharing options...
johnj92131 Posted August 21, 2016 Author Share Posted August 21, 2016 Looks like I have identified the problem - spark plugs! Engine was still missing going up the hill, so decided to pull a plug for a look. Found a huge gap and eroded tip - same issue with all 6 plugs. Last shop I had change the plugs 18 months ago put in a set of "Split-Fire" plugs. I am replacing them with Autolite 985 plugs, gapped to .035 and a fresh set of plug wires on Monday afternoon. The balance of Sunday is filled with Honey Do items. Link to comment Share on other sites More sharing options...
Eagle Posted August 21, 2016 Share Posted August 21, 2016 Looks like I have identified the problem - spark plugs! Engine was still missing going up the hill, so decided to pull a plug for a look. Found a huge gap and eroded tip - same issue with all 6 plugs. Last shop I had change the plugs 18 months ago put in a set of "Split-Fire" plugs. I am replacing them with Autolite 985 plugs, gapped to .035 and a fresh set of plug wires on Monday afternoon. The balance of Sunday is filled with Honey Do items. Some years ago my brother gave me a set of Split-Fires for my '88 XJ. Worst spark plugs I ever ran. I replaced them with NGKs and never looked back. Link to comment Share on other sites More sharing options...
johnj92131 Posted August 21, 2016 Author Share Posted August 21, 2016 Looks like I have identified the problem - spark plugs! Engine was still missing going up the hill, so decided to pull a plug for a look. Found a huge gap and eroded tip - same issue with all 6 plugs. Last shop I had change the plugs 18 months ago put in a set of "Split-Fire" plugs. I am replacing them with Autolite 985 plugs, gapped to .035 and a fresh set of plug wires on Monday afternoon. The balance of Sunday is filled with Honey Do items. Some years ago my brother gave me a set of Split-Fires for my '88 XJ. Worst spark plugs I ever ran. I replaced them with NGKs and never looked back. Yes, never heard a good thing about Split-Fire plugs. Amazing that the shop even installed them. Link to comment Share on other sites More sharing options...
johnj92131 Posted August 23, 2016 Author Share Posted August 23, 2016 Installed the fresh Autolite plugs. Gap set at .035. New spark plug wires just for the heck of it today. Started first time, Idle is smooth. Quick drive up and down the hill - runs great. Problem solved. Thanks for all the assistance gentlemen. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 23, 2016 Share Posted August 23, 2016 Sometimes we all forget about K. I. S. S. Link to comment Share on other sites More sharing options...
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