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06-08-2024, 08:49 PM | #1 |
Registered User
Join Date: Mar 2015
Location: South of Pittsburgh
Posts: 428
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454 TBI surging/loping
I made a thread a few months back about my TBI surging, I thought I had fixed it however its back and appears worse.
so backstory- truck was getting horrible MPG. unknown history so I decided to rebuild throttle body. in process found fuel lines rusted so replaced those. when I installed rebuilt throttle body and did IAC relearn, I was having issues. turned out to be a torn o ring but I had already bought a new one so swapped it. everything seemed ok, but every once in awhile truck would lope- like it had a cam in it. drives great, only does this at idle or creeping in low (truck is NV4500). so here is everything that has been done to the truck: previous mods: new ditsrubutor and coil adjustable FPR (set to about 12 PSI) TB spacer and better air cleaner in past 3 months rebuilt TB with new injectors new fuel lines new IAC new Throttle Position Sensor new MAP Sensor new O2 sensor (heated upgrade) new coolant sensor I dug out my old Chinese tech 2 and figured out how to read the data on the truck. I attempted to set the IAC count down, and it would be good, but when I start truck up it goes right back up. so for example I try to set to 15. its good, restart and its up to 30. I tried doing the IAC reset jumping terminals- when I disconnect IAC the truck lopes VERY bad and barely runs- it was not doing that 3 months ago. I also noticed if Im sitting in the garage and I raise the rpm slowly, it will climb to about 2400 or so, and then randomly drop to 17-1800, and then rise again, and just do that over and over. ive checked timing, its good steady not jumping. I checked for vacuum leaks with propane, nothing. I checked EGR and PCV, both seem good to me. at this point im lost. I dont know where to turn next. every time I think it's one thing and I change it, it runs good for a few miles, then random lope again. when this first started back in march- it was NOT loping when I tried to do IACA relearn, so to me it seems to be getting worse. I have a couple screen shots I took of my tech2 screen today when I had IAC set good and it was idling nice. then I shut off restart and it lopes. maybe someone can tell me if anything looks off? |
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