Captain Dave

I have several Astros, but my current problem is with my 99 Safai, 4.3 Vortec, AWD. While driving yesterday, experienced two sudden momentary drops in power then coasted. Realized fuel low, put in 2 gal, started ok but very little power at low revs and tendency to knock at higher throttle. Performed ok as long as rpm>2000, drove to work mainly in first; dieseled for 5 seconds after ignition off. Nothing obvious under the hood, started easily but still knocking on throttle. Would not start after work, hitched home.
Came back next day with full tools. All fluids fine, air filter ok. Fuel pump runs fine during pre-pressurize and during crank, fuel pressure at manifold >62 psi. Spark present during cranking at all wires, tested with scope and test spark plug. OBD2 daignostics communicate ok but show ZERO problems. Exhaust does not appear to be blocked. Cranks happily as long as I dare but no start.
Any chance it is a sudden death of the fuel pressure regulator in the intake manifold? If the crank position sensor died, shouldn't the computer know that? Anything else I should try before (gasp) towing it to a shop?
Many thanks in advance for any hints.

Thumper_ehhhhh

im not sure what the fuel pressure needs to be but when mind died the same way it was the fuel pump. It would still pump but not enough pressure to make it run. These are bad for fuel pumps. Not sure if its your problem but it was with mine.

ihatemybike

Does it stumble at all while cranking?

Thumper_ehhhhh

It did at first until it completely died.

shop2060

fuel ok crank, cam, coil, and module, are new still not have strong spark and no injector pulse any help welcome

Captain Dave

I should probably close this thread off. After replacing most of the ignition parts (which were all 11+ yrs old and deserved attention anyway) and most of the fuel parts (pump, filter, injectors, computer) with still no change (it would start and barely idle but would stall when throttle depressed, would rev up happily if fuel poured down intake with throttle open), I finally hooked my scope up to one of the injector drive signals. At idle, there was a narrow pulse. When throttle opened, instead of wider pulse as expected, the pulse narrowed slightly and the fuel pressure increased a hair, again the opposite of what you would expect. Scoping the throttle position sensor showed it faulty, and the computer did not know the throttle was opening and was trying to meet the "idle" request from the throttle (under extremely lean conditions due to open throttle). A final weirdness due to a clogged EGR unit and I am now back driving it. Some guys will do anything to keep from changing their snow tires over. I have been driving my lady's 1989 Taurus SHO, and the van is much more relaxing. Thanks everybody for suggestions.

ihatemybike

Thank you for coming back and posting the resolution.