2.8 TBI V6 - Won't run with MAP conn. after TBI rebuild

[armyBob]

Arrgh! Well the o-ring didn't fix it. I tested compression again and they are 180 psi all around. Why so high? Carbon deposits maybe? How hard is it to jump the timing chain? Also, if I am able to get it to run, it is backfiring a lot in the intake, but spark timing is correct and no vacuum leaks that I can detect. I've about had it, and am about to go to a professional. I would have gone sooner, but money is tight. Exhaust backpressure wouldn't make compression high would it? I pulled the o2 sensor again anyway.

[geoffinbc]

If number 1 is on TDC Compression (you absoutley must verify the compresion stroke) where does the rotor on the distributor point?

From all this backfiring through the intake your MAP sensor will be fucked. It cannot take that abuse. Im am pretty sure you can buy O-rings at the dealer.

[armyBob]

I figured the MAP sensor was a gonner at this point.

I had removed the rotor to check the ignition module (never did actually check it though), but it is keyed so it only fits on one way. Sure does seem like it's 180 degrees off or something. I'll check the orientation of the dist ASAP.

Chevy doesn't carry the o-rings individually.

I did check with ECT and ESC disconnected, no change.

Thanks so much.

[armyBob]

Rotor is aligned with 10*BTDC on compression stroke of #1 cyl.

Pickup coil resistance is about 800 ohm.

Ignition module - Tested BAD (once hot) at Autozone. Will replace.

Rotor looks a little worn but okay, will probably replace also.

[geoffinbc]

Yea ignition module may be a major contributor.

Where in the truck does the rotor point when on #1 TDC compression? Like 6 o-clock 7 o-clock 8 o-clock?

[armyBob]

About 7:00. It is slightly in the counterclockwise direction from the left mounting screw.

[geoffinbc]

Ok thats good. Have you changed the ignition module yet?

[armyBob]

No I'll probably do it tonight. Thanks!

[armyBob]

IT'S FIXED! The new ignition module did it. I can't explain how rebuilding a TBI unit would fry an ignition component, maybe it's a bizarre coincidence, but it works now!

I still have that issue with the oddly grounded injector. I tried swapping pin D16 to pin D15 on the ECU, but no difference. So the ECM must be bad. In any case it seems to be running the same or better than it did before (idles better in open loop) with the injector permanently grounded.

And the GM MAP sensor (which I think is the original) is still working fine after several loud backfires (one of which popped out the PCV valve).

Lesson learned: no matter what stuff you've done, if it won't start, return to the basics - compression, spark, fuel.

I'll be changing the oil immediately since it smells like fuel and I have a lot of ticking (diluted oil?).

Thanks to all especially betterthanyou (I owe you a cold frosty beverage).

[geoffinbc]

OK lastly. WHERE is this injector grounded? I cannot believe it is constantly grounded. Go buy an injector Noid light and test the injector connector. if it is pulsing it is working.

A multimeter will probably show a constant ground when the truck is running because of the speed the ECM is switching the ground on and off. A constant 12V supply should be present on one side of each of the 2 injectors. The other remaining sides will be switched via the ECM on 2 seperate connections.

[armyBob]

To the "meter" fuse, which is grounded via the main relay I believe. At first I thought it was using 12v from this fuse, but the fuse is on the low side not the 12v side of that circuit. As I said the wiring to the ECM isn't faulty (blue wire in my case) - good continuity. According to the info I have pins D15 and D16 are ganged together. It was on D15, moved it to D16 to test. However, it still won't run without the spliced wire to the fuse box. If the ECM (1228062) is bad i can get one from a salvage yard for $50. Seems a bit steep, I think I found a reman'ed one on Froogle for $80.

[geoffinbc]

Fuses are never on the ground side of the circuit. They always have 12V power.

The white and red injector wires should both have 12V power from the EMCI fuse. The are however spliced into a pink/black wire which is what you would find in the fuse box

The blue wire goes to D16 and the green wires goes to D14

There is no relay involved in the circuit