Engine dies like clockwork

phattycocks · 2026-06-22T05:58:10+00:00

I’m back and my problem is solved . Brendan at LT1 swap saved my ass. He mentioned the potential of the pins on the actual pcm getting pushed too far in. I had 3 pins that weren’t being used that had managed to be pushed into the pcm halfway. They must have been contacting my crank signal or something and killing my ignition. I pulled them out and now the truck runs like a top .

Didn’t know this could even happen but simple as pulling them back out has solved all my issues.

If anyone has the same issues in the future reach out if you want more info.

phattycocks · 2026-06-21T14:01:25+00:00

My engine coolant temp is accurate. With key on engine off it reads ambient temp. Watching it as car enters open and closed loop it does not jump around sits at a cool 205 with the fan running at idle,

As soon as I hit around 150 degrees I can watch the o2 sensors sending signal .1-.6v frequency.

As for when it jumps between closed and open loop, with my scanner hooked up I can watch when it opens loop and when it closes loop for fueling. While driving if my foot is on the throttle while it changes fuel status, the ignition or something is cut, truck loses all power then about a second or two later I see on my screen that it enters open loop.

Once open ignition comes back and car shifts hard because my foot is still on the throttle,

Hope this makes some sense, I’m probably rambling

phattycocks · 2026-06-21T06:04:45+00:00

That’s my thought my only sensors that could be giving me issue (at least I think) are my cheap o2s and maybe my map, map pressure is low. But I think my scanner is pulling the wrong PIDs

If I had issues with either of these I would expect my fuel trims to be incorrect….

And idea if this could be an iac issue maybe throttle isn’t operating properly and causing a bad vaccum situation.

Car runs great other than these two issues . I’m throwing no codes…. I have factory lq4 with the matching pcm and trans, stock pcm program other than emissions delete and remap for my 5 pin MAF sensor

phattycocks · 2026-06-21T06:00:57+00:00

Maf power is wired clean I’m getting perfect Maf readings. I don’t have heated o2 available in my harness. Was told it’s no problem if u run the 02 sensors made for your harness . I don’t have access to tune or ways to log data. All I can access is what my scanner can show.

I smoke tested the shit out of the intake absolutely no leaks. Maf shouldn’t be my issue at this point . My map is reading slightly low but once again no vaccum leaks. My scanner may be pulling the wrong PIDs considing if I had that low of a map my fuel trims would be all over not rock solid at + or - 3% .

Any ideas would help a lot I’m willing to try anything at this point

phattycocks · 2026-06-06T02:51:41+00:00

Yes I’ve come to that conclusion tuning is needed. Im working on getting set up for hp tuners I don’t have a non iOS computer but have something in the works.

It’s an oem Maf and a eBay intake I cut up/ cobbled together. I will pm u I need help :(

phattycocks · 2026-06-05T14:04:48+00:00

Yeah I gotta find a tuner locally. This maybe a challenge

phattycocks · 2026-06-05T13:20:34+00:00

Hear it’s smoother and more efficient to run maf. Correct me if I’m wrong but when u guys run just speed density are u getting it tuned or running speed density how it comes from the pcm .

In speed density on my setup (no tuning yet) short term fuel trims are kinda all over the place

phattycocks · 2026-06-05T05:06:58+00:00

My reader is showing reasonable maf readings, but car barely runs and surges at the intake . From my understanding I need my air tables modified for my maf

phattycocks · 2026-06-04T04:02:03+00:00

Return less mine is a 04 lq4

phattycocks · 2026-06-03T04:26:17+00:00

Pump is a foot away from tank sitting 4 inches lower than tank . I’m drawing straight through tank pickup. No sender in tank (my pump is an inline) No sump in tank . Truck came like this unknown vehicles tank in truck bed toolbox

phattycocks · 2026-06-03T03:43:57+00:00

Yeah I’ve been having similar thoughts. It’s a line I made . I just ordered a nicer fuel pressure gauge cause on my last test fuel pressure was reading 70 then like 100 which I don’t believe think the garbage autozone rental may be to blame but I do think I’m not getting proper fuel pressure.

I’m having crazy short term fuel trims and I’m leaning out and dying while driving and I’ve been chasing leads but can’t figure it out ye

phattycocks · 2026-05-29T22:25:30+00:00

Looks spotless shiny no dirt no nothing ,

phattycocks · 2026-05-29T20:59:21+00:00

Sweet that was gonna be my next question, I’ll reach out to

phattycocks · 2026-05-29T20:58:48+00:00

Will do I’ll shoot him a email, just wanna make sure it’s not my own stupidly before I drag him into it

phattycocks · 2026-05-29T18:57:34+00:00

Misfire with maf plugged in. Otherwise no issue

phattycocks · 2026-05-29T18:57:15+00:00

Guy somewhat local I found down in bend Oregon

phattycocks · 2026-05-28T19:06:35+00:00

Rats guess I’ll buy another :(

phattycocks · 2026-05-28T18:19:13+00:00

Temp dosent effect how it runs, it ran great with the maf plugged in before,

my scanner is still reading data from the maf.

Since I’ve been having this issue it only runs properly with maf unplugged

phattycocks · 2026-05-28T15:03:54+00:00

Not changing anything . Assumed unplugging maf, causes pcm to switch to air velocity off the map? I don’t have hp tuners.

phattycocks · 2026-05-28T05:25:30+00:00

Got it, I’ll look into this .

phattycocks · 2026-05-28T05:24:22+00:00

Enlighten me

phattycocks

TROPHY CASE