1994 Z-71 Cold start Runs bad 30 seconds??

[Durfman77]

I just got done putting new fuel pump in [$166] and we will see tomorrow AM I guess? Most time I take relay out and run to relieve pressure in line but did not this time, I started drove into garage and [cheated] cut hole in bed to get to pump and cracked the lines and Nothing? No pressure at all? Seems strange?

 

[Bextreme04]

I just got done putting new fuel pump in [$166] and we will see tomorrow AM I guess? Most time I take relay out and run to relieve pressure in line but did not this time, I started drove into garage and [cheated] cut hole in bed to get to pump and cracked the lines and Nothing? No pressure at all? Seems strange?

Did the soft line from the pump in the sending unit look old and cracked? Do the TBi trucks use a return line system with a pressure regulator? Could be a fuel pressure regulator bleed down issue I guess. You know you can rent a fuel pressure test kit form most auto parts stores for free right? Why throw $166 part at it when you haven't diagnosed whether that was the problem? Also, rockauto has the pumps for $15-30... You can get an entire AC Delco pump and sending unit on there for $120. Who charged you $166 for just a pump?

 

[Durfman77]

The soft part of line was not tight? I got pump at Auto-Value here local--I know I should do this different --Really not like me to throw parts at something but last two weeks been crazy around here and with my back&knee problems I am just tired of working ob stuff to tell the truth.

Couple people recommended fuel pump and this was the original so thought I get lucky??? Find out tomorrow?????

 

[Durfman77]

Well Just tried starting truck and I think its ok now? It started fine and about 20 seconds just stumbled a very little for maybe 3 seconds then fine? Nothing like it use to do so is it fixed? Will drive today check that out also,

 

[peats]

reading this post reminds me why i drive vehicles with carbs and no computers. i just don,t need that noise.

 

[Frankenchevy]

reading this post reminds me why i drive vehicles with carbs and no computers. i just don,t need that noise.

Carbureted engines are definitely more simple, but the TBI engines will probably outlast any other Chevy from any generation.

 

[Bextreme04]

Carbureted engines are definitely more simple, but the TBI engines will probably outlast any other Chevy from any generation.

I must say I disagree with all of that. I personally find the OBD1 fuel injected engines to be the worst of both worlds. They aren't sophisticated enough to be significantly more efficient or reliable and they also aren't smart enough to tell you reliably why they aren't running right.

I personally think the sweet spot is the 95-2005 MPFI engines like the L29 454 and the L31 350's. They make great power with good efficiency and will easily last 250,000 miles while getting 15mpg or better. The OBDII system they use is simple enough to do your own DIY tuning for cheap and it will tell you EXACTLY what the issue is.

Carburetors give you none of the reliability or efficiency. You can dial the min for the specific condition and environment that is present when you tune the carb, but anything outside of that is totally hit or miss. Tuned at sea level? Good luck going up into the mountains and having it run right. Tuned when hot? Good luck in the winter time.

 

[Frankenchevy]

I may be wrong, but the tbi 350s I’ve been around have definitely outlasted the vortecs I’ve been around. Both of the vortecs my dad had experienced fuel injection issues before 200k, but his tbi burb and 1500 both had more than 300k when sold. My uncle and my buddy’s uncle have 94 burbs with almost 500k. Maybe it’s just a luck/bad luck scenario.

I remember a mechanic telling me once, that GM made a big mistake with the tbi gmt400s by making them too reliable. There again, second hand knowledge.

 

[Grit dog]

Nice truck!
Not many back east that haven't died of cancer by now.
I was going to suggest faulty IAT, but the fact that it runs great except briefly, same time everytime, idk if that's it either.
Worth checking though.

What's more concerning is that May 12 in MI and it's still brown there!
I know you guys have had a poor spring in the Midwest, but dayum!

 

[Durfman77]

So the fuel pump issue would be this. It bleeds down over night and the fuel is replaced with air in the lines, you turn the key on and it pressures up, there is still fuel in the fuel rail, but there is now air in the lines, so it starts on the fuel in the fuel rail and then when it gets to the air it runs bad and once that is clear it is good all day. This is a problem I've seen on that generation chev truck before, testing the fuel pressure should help you identify that. BUT there's other sensors, that if monitored on a scan tool you might find one out of whack. Bottomline is tests need to be run, or you may end up spending a lot of time on money on unneeded repairs.

Well after a new fuel pump and I rebuilt pressure-regulator it still the same? AND a new Temp, sensor in cooling intake manifold also no change??

 

[SirRobyn0]

Well after a new fuel pump and I rebuilt pressure-regulator it still the same? AND a new Temp, sensor in cooling intake manifold also no change??

I will think about this some. I really thought that the pump would fix it. My knee jerk reaction at this point is you may have read the system on a scanner and see if there are any odd sensor readings when the truck is cold. I'll post again tonight after I've thought a bit about it.

 

[Ricko1966]

Put a fuel presdure tester on it check your pressures.Turn it off see if it holds rest pressure you could be bleeding fuel into the cylinders, so next time it starts you have some cylinders that are flooded.

 

[Durfman77]

Well all summer it starts ok now colder out and here we go again?? Might take it to local shop? I am out of ideas?

 

[Catbox]

After the last Seafoam I poured through mine it hasn't done it again.
Mine has a newer pump in it as well.

We shall see how this winter with it goes...

 

[Durfman77]

After the last Seafoam I poured through mine it hasn't done it again.
Mine has a newer pump in it as well.

We shall see how this winter with it goes...

Did you put it just into the TBI unit while running??