Engine Hesitation at light throttle!

JGPRO2003

MEMBER
1994 CHEVROLET SUBURBAN

I'm trying to get my truck back on the road after sitting in my drive way for a year. I would turn it on every couple of weeks or so but no driving. The truck was dying out on me while driving, no spark, turns out it was a bad oil pressure switch. Since fixing that problem truck starts every single time. I have replaced various items in an attempt to bring it back in good road condition (timing module, pick up coil, ignition coil, AIC valve, EGR valve, checked ignition cables, checked ground to ECM. Set timing to 4 BTDC with the EST wire disconnected. Now the problem is while test driving the truck it will idle fine and hold idle while in gear but when taking off it will bog down after a couple of seconds. Sputters and bucks and won't completely stall. Whats strange is it idles fine and takes off just fine for at least the first couple of seconds. I checked the VSS and looks good. One thing I have noticed is after I reconnect the EST wire the timing retards a boat load! Maybe 20 degrees or so, Help!

350, TBI.

4 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

Weird things happen when a vehicle sets for a while. Rodent chewings included.

Are there any codes in the computer?

Are the egr passageways clear?

Just to clarify, are the symptoms present before it goes into open loop?

Have you checked the fuel pressure when the symptoms occur? Too high-fuel pressure regulator, too low possible fuel pump. Spec is critical.

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Wednesday, October 7th, 2009 AT 6:30 AM

JGPRO2003

MEMBER
6 POSTS

I replaced the EGR valve and the passages on the intake looked clear. Fuel pressure holds steady at 10 psi. No codes ever, except when disconnecting the EST wire when setting timng. As far as I can tell condition is present in open and closed loop.

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Wednesday, October 7th, 2009 AT 10:38 AM

SERVICE WRITER

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9,123 POSTS

Re-check the egr. I know it's new. New parts are are not always good parts. It is a very easy test- when the engine is off, put vacuum pump on EGR valve and pump- valve should not move at all. If it does, it is junk.

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Wednesday, October 7th, 2009 AT 7:42 PM

SQM

MECHANIC
6,383 POSTS

An engine can hesitate due to a number of reasons. It could be due to low fuel flow, vacuum leak, clogged air filter, dirty mass air flow sensor, worn spark plugs.

Take a look at this guide, it covers the typical issue with engine hesitations:

https://www.2carpros.com/articles/engine-hesitates

Also, it will be a good idea to test the EGR valve to make sure it if functioning properly.

Here is a video of how to do that:

https://youtu.be/DqUCbbKdWf4

Clean out the EGR tube can also help.

Please let me know of any questions.
Thank you.

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