Alright, for the sake of electronics, lets call my truck an 87 TBI 454. It actually has the edelbrock tbi-mpfi conversion, but it utilizes the factory computer, wiring, & sensors. Now as for symptoms.

Yesterday went out, drove maybe 2 blocks from my house, and it started spitting and sputtering, idling really low (400rpm) and generally poor. So I checked the computer chip as it has popped loose before and given similar symptoms. After that, it fired up and ran just fine.

So today, I go to leave, get 3 blocks away and it starts makin a noise like an exhaust leak. Sounded like one of those delivery trucks with their massive exhaust leaks. Came home, parked it, took my moms jeep to school. Came home to start diagnosing, and the noise isnt exhaust. It was coming from the area of the torque converter/flexplate. Pulled off the inspection cover, and checked the TC bolts, 2 werent all the way tight, and looked over the flywheel as best I could for cracks.

Fired the truck up, didnt hear the noise, so took it for a testdrive. Got about halfway around the neighborhood and the noise started again. Got 2 blocks from my house and it started surging, spittin, coughin. Got home, killed it, checked the chip again.

I also changed the ignition module since I had another sittin on the shelf, and Ive had those cause weird issues in the past. Now the damn thing wont even start. It just backfires up through the throttle body when you try to start it. I swapped ign modules back thinkin maybe the new one was bad out of the box, still just backfires through the throttle body.

I checked, it is getting fuel, and it is at the correct pressure, it is getting spark. I am running a msd distributor (8366) and a msd 6al. Spark appears good and strong. I hooked up a multimeter between the 2 wires on the pickup coil and its got ~550ohms, and msd says it should have between 400 & 1300, so it is testing as good.

When you try to crank it, it just pops back up through the throttle body and if you mat it, sometimes it will fire and run VERY poorly, constantly popping up through the throttle body, like the timing is extremely retarded. I dont have a 2nd person to check timing, but going off how I aligned the cap when I installed the motor it doesnt appear to have moved, and the holdown is tight.

Does anyone have a clue as to what to check next? Im at wits end with this thing, does anyone have any ideas as to what to check next before I blow this thing up?

Long post, so I appreciate any help guys.
Thanks guys.

 

Since I posted, I have swapped out the oil pressure switch, thrown in a spare coil, and still nothing. I pulled the ECMB fuse to kill the fuel system, and cranked it over to clear it out, it ran......decently.......for 3-4 secs and then died. I put the fuse back in and its dead again, so its possible its just flooding out.


This sucks, anyone have any clue where to even begin? Maybe some good diagnostic charts?

 

Might as well throw another update on here, I found 3 plugs left from last time I changed spark plugs, I put em in, started the truck, and it actually started and ran for about 6 seconds before it died. I ran around to the front of the truck, pulled those plugs out and poured the gas out of em.

So its confirmed it is running EXTREMELY rich.

 

time for the hourly update

I went out to try it again after reading any and everything on the internet about TBI, and I noticed an anomoly, when I am cranking, the tach is showin 6-700rpm, when the truck tries to catch, it kinda gurgles, the tach starts dancing between 4 & 6k rpm. The tach is hooked to the side of my msd box, and the msd is tied into the factory wiring w/ msd adapters. Argh.

All of this, Im thinkin it might be the pickup coil sending out wacked signals

 

sounds like it, cause if I'm not mistaken if the pickup coil is shot the tach will either not work or will go haywire.

 

Well, just finished replacing the pickup coil, truck fired up and ran for about 30 secs, blowin all kinds of gas smoke out the pipes from yesterdays flooding, and then it popped out the throttle body a couple times and cut itself off

 

Just ran MSD's tests and the box checks as good.....

 

have you checked the timing? Not sure what else to look for given it ran for 30 seconds but then backfired and died.

 

Well I threw a spare computer & chip in, no change. Put in a new set of plugs, now itll run, but it just constantly spits back, everytime it pops little puff out the tbi.

Checked the timing, base appears to be about 4*'s which is good according to the sticker on the core support. With the EST hooked up, it was ~40*'s, so much for retarded timing. Is 40 a good amount, or is it just too far advanced now?

 

40 degrees at idle? Yeah, that would be too much. That's about as much as you would want for total advance.

 

Then what could be causing this thing to jack itself up 36*'s just by pluggin in the EST. Also this could be a little above idle, I wasnt in the cab, I was runnin the gun, and my dad was having to play w/ the throttle to keep it runnin at times.

 

Some of the things you describe sound like a timing problem. Like maybe some slop in the timing chain. But that's just a guess.

 

Yeh, I thought about that, but the motor only has ~25k or so, never been over-revved or anything. The other thing is, it was doing it, then it quit, and then it started doing it again. Just checked, cats arent plugged.

 

Still fighting this issue guys. I changed the plugs, so I can get it to fire up & run now, its just sittin there popping through the throttle body.

I since change the cap/rotor, bypassed the msd box, tried the diff comp/chip, put in a gm ignition module, and tested the spark plug wires with an ohmeter. Just came in a few minutes ago, from sprayin the wires down with water and starting it when its dark. No arching was visible between the wires. I swear it sounds like I have 2 wires switched, and no I dont, already checked that.

Im almost down to thinking its something mechanical, valvespring, pushrod, etc, but the thing is, I have true dual exhaust, and both banks sound the exact same.

 

K20, you said it seems to be running rich and that disconnecting the fuel pump seemed to smooth it out untill the pressure blead off. Have you checked your injectors and or fpr or any fuel related parts? Hope you find your problem.

Steve

 

Yeh I checked my fuel pressure the last day I posted, it was pegging the gauge at 60psi. So I ordered a new FPR, just got it today and installed it. I shorted the pumps to 12v to make em run and it was showing ~50psi. Ok, so I started the truck, gauge pegs out but its not poppin out the intake at idle.

If you even rest your foot on the gas though,it will start popping again. ARGH!!!!

What now?

 

http://i13.photobucket.com/albums/a2...22-07_1502.jpg found my issue........