1991 454 GAS MOTORHOME WONT RUN BACKIRES MISSES SURGING HARD STARTING SOMETIMES RUNS PERFECT FOR A SHORT TIME, CANT FIGURE OUT WHATS WRONG WITH IT

10

Asked by Apr 18, 2018 at 10:06 PM about the 1991 GMC Suburban

Question type: Maintenance & Repair

Just installed rebuilt (3 years old approx) 454 into Chevy P37 Class A
motorhome. Started right up after install. Ran fine, except motor abruptly quit
after about 45 min or so run time. (Idling in yard; ran up the road a 1/2 mile
no problems; quit while idling for long periods). Also have excessive draw on
starter battery; runs down overnight. Rebuilt engine came with new
distributor (3 years old again) and was using that ignition module.  (motor
home wasn't running when I bought it; towed it home; ruined motor from prior
idiot owner).  Changed to original module; ran poorly. Took both modules in;
both failed. Bought new one, but before I took old one out, I disconnected
wiring buss with 6 hot wires (one from battery; one to alternator; one to
computer; 3 to ??) looking for excessive draw, and dropped buss while
engine running. Shorted out; lots of sparks. Engine died immediately. Tied
buss off to the side, fired and stalled. Fired and stalled. Many many times.  
Installed new module in distributor; Ran for 2 seconds and stalled. over and
over.  Finally tried to accel when starting and got it into this loping galloping
RPMs up and down, but stalled at idle. Ran at increased rpms and it finally
smoothed out. Idled fine. Next time I started it, back to galloping. Timing light
says firing is 2 cylinders off which is impossible to run at that. I had set timing
to TDC with install, and rechecked. Not a vacuum leak. New intake gaskets,
no brake booster (hydraulic), no other vacuum leaks even though that would
describe this condition. Everything happened after shorting out wire. WHAT
did I fry??? If computer, would it still run in this galloping mode? Bought new
coil; no difference. I'm guessing 1st module caused the stalling after 45min.
2nd module simply bad. Shorting out wire did the damage, but what???

1 Answer

10

Correction on timing. It's fine. Class A motor home has to use an alternative timing point than #1 as you can only go from the bottom. I miscalculated which cylinder to use...

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