Rough starting...

[captain1]

Hello all,

I have a '94 S-10 4.3 L 2WD Vortec Red (enough details? :-) when I crank it up it starts right up, but shakes and jumps for about five seconds, then smooths to a regular idle. I recently tuned it up, but still occurs. I'm thinking it could be either a fuel pump problem or possibly the MAP sensor. Any suggestions? Thanks!

the Capt.

[busa_4]

check your fuel pressure. shakes and jumps can be caused by a temp lean condition. what do you see out of the exhaust when this happens? it could also be a rich condition as your cpi unit might be leaking fuel into the intake while it is sitting and when you start it up it is rich causing the stumble until the excess fuel is burned. check your cpi unit for washing.

[j.patelia]

check the o2 sensor. It might be out of whack..

[Mikado14]

The O2 sensor does nothing on a cold start, it is in open loop.

[j.patelia]

Why did I say o2 sensor..I meant to say check the vaccum tubes. There might be a loose connection..sorry about that..

[gbic1]

Test your fuel pressure first. This engine like all newer gm truck engines need a lot of fuel pressure to start but not as much to run. See if you get the correct spec for you car at start up. as litle as 5lbs will make a big difference in these.