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ksengage31, ASE Certified Technician
Category: Car
Satisfied Customers: 61
Experience:  Master Certified Technician Specialist in driveability and engine diagnostics.
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1992 chvy pu with 4.3 ltr..speeds of 20..sputter..carb i..egr valve

Customer Question

i have replaced every thing but the motor it is a 1992 chvy pu with 4.3 ltr at idle or driving at speeds of 20 or so its fine but when u get it up to 65 or in between it wll spit sputter and back fire trough the carb i have timed it checked the egr valve u name it
Submitted: 4 years ago.
Category: Car
Expert:  ksengage31 replied 4 years ago.

ksengage31 :

Hi, my name's Jesse and id be happy to offer you some help today.

Customer: replied 4 years ago.

what info do u need

Expert:  ksengage31 replied 4 years ago.
Like any other model of vehicle these trucks had common issues i could guess at and recommend you check for. However, if you have any other info about things you've tested for me to consider it would help us get to the bottom of things. I understand how frustrating these things can be if your changing parts and not getting anywhere.

A few things that come to mind first -
Is there a check engine light on at any time? Can/have you retrieved the codes?
Have you been able to test the fuel pressure with a gauge? If so what psi shows running?
Can/have you verified that the timing advance is working properly, with a timing light?

Customer: replied 4 years ago.
it has a brand new fuel pump presssure is good 12 psi the injectors have equel spray and as far as i know or could check timming is right on none of the plugs are fouled
Expert:  ksengage31 replied 4 years ago.
Let's look towards the ignition system first in this case then. Although it sounds like an obvious question, has the distributor cap and rotor been changed? they are notorious for causing issues on these engines. Typical for them to cause strange symptoms at speed, but not at idle (due to the cross-arcing inside a worn cap.)
Also i would suggest to check the condition of the pickup coil in the distributor (remove dist cap to access) , if not already done so. Look for corrosion at connections, brittle or cracking wires that may be going intermittent/short, and test it with a meter. With the pickup coil unplugged, measuring in ohms from one terminal to the other, you should see resistance between 500-1500 ohms.

If these tests don't turn up anything suspect, we can move on to the next ones.