GM TBI Problem-Need help!

[SpeedMetal]

The wife's Blazer is running rough-it's an 89 with a 5.7 and TBI. Under acceleration, it stumbles and almost dies. However, at constant speed and at idle it runs perfect and has good power. I've replaced the TPS, fuel pressure regulator, fuel filter, cap and rotor. It's also hard to start, sometimes it takes 5 or 6 tries. I'm thinking now that the fuel pump isn't putting out enough pressure. Any and all help is much appreciated.

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[matt_helton]

deffinetly could be the fuel pump. those pumps are real cheap even for OEM.

also for kicks, check the timing and make sure the distributor hasnt moved at all. and dont forget to dissable the ESC by disconnecting the tan single wire connector on the pass side of the fire wall.

and how old are the plugs and wires?

[SpeedMetal]

The plugs and wires are fairly new....I'm gonna try replacing the fuel pump tomorrow and hopefully that'll do it. I just hope it gets me home tonight....

[FABRICATOR]

The MAP sensor plays a major role in throttle response.

[SpeedMetal]

Well, the fuel pump didn't fix it. I'm thinking that the MAP sensor will probably be the next step. Would a bad MAP sensor make it hard to start? I barely got it to start today, it took like 10 tries. It's idling and running at constant speeds really good. Just off-idle starts anything past 1/4 throttle are horrible, almost dies and the starting sucks. Thanks again for the help.

[matt_helton]

did you check the timing? how many miles are on this motor? ive seen timing chains become stretched over time and actually skip a tooth on the crank or cam causing problems like you are having.

map sensor, ok......but shouldnt cause hard starting.

id also check the coil output.

could also be an ign. module/pick up coil taking a dump.....which means distributor overhaul.

id also check the egr operation.....make sure its not stuck open.

[Ryno]

a couple other things to check....IAC....vacuum hoses, the pcv valve, and the EGR. My 94 k1500 was real touchy when any of the above was dusted. Distributor is $100 from autozone. A coil is like $30. check them both, I had problems at least 5 times with the coil arcing.

[FABRICATOR]

My bad, I didn't see the hard starting part in the original post. Most everything starts in open loop anyway. Are you getting a good spark while cranking?

[SpeedMetal]

Tried to start it this morning, no go. It only tried to fire for one brief second. I'm thinking I'm gonna try the module now....I'll check out the timing and coil output as well. The motor has about 25,000 miles on it, and runs really good(just not right now).

[matt_helton]

25,000 or 250,000?? didnt you say it was an 89? or is it a second motor for the truck?

when your cranking it can you see the injectors squirting fuel down the TB?