Timing problem with 89 G-30 Van

[Piston]

Timing adjustments are pretty straight forward... But it sounds like there is more to this than just timing adjustments. Backfire's are usually associated with ignition problems but weak fuel pressure can also cause this. I seriously doubt its a ECM failure or even a sensor of sorts.

Fuel pumps plagued these vehicles from day one. TBI only runs 9-13psi and if its not within that range it will run like crap. 7psi will cause unstable idle, backfire's through the intake and sluggish performance. Problem is, owners didnt change the fuel filter enough, which overloads the pump and wiring.

Throwing parts at a problem will eventually get it done (sometimes) but I'm willing to bet its a "basics" problem.

Have him verify these things:
-- Ignition pattern. Verify proper saturation dwell time from the ignition mondule. How's the secondary pattern and KV reading. If there is a burned rotor, it will show up there!

-- Fuel pressure @ idle and full throttle (should NEVER be less than 9psi)

-- Good injector spray pattern. He can check this with a timing light to see a perfect cone spray pattern.

-- Find out what the block learn/long term fuel trim is reading. Should be 128 on both.

-- Timing adjustment. Inside the cab, passenger side, under the heater box ( just above the carpet) you'll find a harness. There will be a black/tan wire with a very small connector, disconnect it. Your now in service mode and can set the timing. The check engine light will come on to let you know its in the correct mode and will stay on until you turn the key off, reconnect the timing connector, then restart. You'll set the timing with a regular timing light connected to #1 wire. Set timing @0 degree's

There are times when a vehicles timing can be adjusted to compensate for a weak pump, but this only lasts for a short while.

Have him give you answers to those questions I've asked and also how he's setting the timing. If he can't figure out how to check these basic FI basics I've listed.... You might concider finding someone that does. These are readings that GM has used for over 20 years. I hate to bash another mechanic but lets face it.. there are plenty of mechanics, not as many techs.