New Fuel Pump — Same Problem??

[Donne Trav]

Finally found an AC Delco outlet in my neighborhood not far from my
job. Purchased a FUEL PUMP & FUEL FILTER. Installed my first fuel
pump—had a few small problems, but hooked it up. Problem is, the
car still has a "rough" idle as described in prior threads. Have not
put the filter in yet, but I can't believe that would fix the problem. The
car almost feels like a "miss/knock" from a bad OPTI SPARK. Man, I
hope not. QUESTION — should I proceed with the fuel filter and maybe
get a fuel pressure reading for possible BAD INJECTORS or have the
OPTI checked, if possible. I was really hoping the new pump would
solve these HARD STARTING issues and roughness. What should I
do at this point?

 

[Hib Halverson]

Typically, a fuel pump replacement will have no effect on a "rough idle" but...you already know that.

Leaking or fouled injectors will have an effect on idle stability. You can begin the process of diagnosis by obtaining a factory service manual and running the fuel pressure tests listed in the book. Usually, those tests will help you decide if you've got a bad injector.

"Rough" idle can be (note: I say "can be" and not "is") caused by a problem with the distributor but, before I'd buy a new optispark unit, I'd correctly diagnose the miss to make sure it's not being caused by something else.

The service manual contains diagnostic information for both rough idle and hard starting.

 

[kcrick]

I saw an entry in another thread that had a pretty cool trick to check the opti. Attach a timing light to the coil wire that goes to the opti and shine it on anything to see if you can tell if there's a miss. I've not tried this and it would seem that it would be hard to tell with the light flashing so quickly, but it may be worth a try....