C-wade7

I put a 88 1500 tbi set-up on an ford 351 that was carbureted. Idle is good and it will run on the road ok but when attempting to accell from a stop it backfires like its lean. The map test ok, 1.0-1.3 at idle 4.75 engine off and when back probed and running it responds to vacuum changes normally. Timing is set to 0* with spout disconnected. Right about 10* spout connected and running. I'm using the ford distributor with vac and mechanical disabled and gm module and coil. Fuel pressure is about 11psi. Throttle position, coolant temp and o2 are working ok. Any ideas what to check??

C-wade7

On another note the ford distributor is fairly new. What I wonder about is it turns counter clockwise and the gm turns clockwise. I wouldn't imagine it would affect advance from the esc module but not real sure? I have read several other post about backfire concerns, but no real help.

RBob

iTrader: (1)

Could likely need more AE. Also check that the fuel pressure is stable, even the slightest drop off in pressure needs to be corrected.

Another thing to try is to set the base distributor timing at 6* BTDC (EST/BYPASS open). This will add 6* of spark advance across the board.

There is quite a difference in the tuning between a peanut cam'd swirl port headed engine and your 351.

RBob.

Formula 305

What have you done to tune it? Sounds like you're using the GM computer? Is it lean or not? What are your sensors telling you?

C-wade7

Thanks for input guys. Stock 351 in a 1 ton Grumman Olsen van body. Stock 7747 ECM, I have a friend with laptop tune capability and the piggyback needed to to put programmable prom in, but he's hard to pin down for any amount of time. I am really starting to think the spark advance may be retarding instead of advancing due to opposite trigger rotation. I color coded the timing marks and am waiting for the wife to get home and rev it while I monitor timing marks. Does that seem plausible to you, that it would retard instead advance?? It seems rich at idle but when warmed up the o2 cross counts and fuel block is 125-6 at warm idle

Schurkey

Delco modules (and pickup coils) are not specific for CW vs. CCW distributor rotation. The pickup coil cannot tell the difference, the signal it sends to the module is the same either direction. Therefore , the module cannot tell the difference, either.

Backfire on acceleration: Retarded timing or lean fuel mix. Either one causes fuel mix to still be burning when the valves go to overlap. Intake charge ignited--pop!

Another cause, of course, would be failure for the exhaust valve to open properly--failed cam lobe, bent pushrod, rocker arm out-of-position. But you'd have backfire all the time, not just on acceleration. (would be worse with more-open throttle.)

C-wade7

I know pick up doesn't care as far if firing but I wonder about the algorithm in the esc that advances. If it is looking at pick up speed and decides it need to fire just say 10m/s before pulse that is actually after tec in that rotation. I unhooked timing controll and set base timing to 12* before and drove it with out any spark controll and it was way better. I then reset it to 4* and re-connected the tan/black wite and unhooked knock sensor and it is backfiring again. With timing light on it it is 0* unhooked, 10* plugged in, but on quick tip in it goes retarded to 10* atdc then planes out to 20ish.
Thanks for the responses and keep the ideas coming!!
Coley