1990 ST.Thomas built GM - Can't beat miss and stumble

[dawg57]

Got my dad's 90 GM sortly before he died. Car had sat for quite a while, but short of a rotting exhaust system from inactivity ran good. I decided to drive it a while to blow the cobwebs and carbon out with the intention of finding it a good home. Then the fuel pump took a dump. Checked relays,fuses, etc. to confirm but since car was a spare took my time about fixing it. Finally got around to pulling the pump a couple of months later, verified that it was dead and replaced it. Car fired right up but I noticed an obvious miss that hadn't been there before. It was almost like a plug wire was off or crossed. So I started to check for damage. Found that the coil tip was about half gone. Looked like maybe it had oxidized and deteriorated while it sat so long during my dad's illness. Replaced the coil and it made no difference at all. Checked the firing order and wires and decided to replace the wire set. Went ahead and got new plugs,cap, and rotor button while I was at it. Absolutely no difference! Pulled a couple of plugs and found that they were fouled as if drowning in fuel so I turned my attention to the TPS and fuel regulator. Replaced both to no change whatsoever. Since the pick up in the distributor was the only component left I pulled the distributor and installed another pickup [even though testing said the old one was okay].Reinstalled the distributor with the same results. No improvement at all. Thinking I might have been off just a hair when I installed the distributor, I pulled out the timing light only to find that this engine has no timing tab pointer on it. Did they even put timing tabs on these engines since it's not normally necessary to have to play with the timing? If I set the timing dead on which is supposedly 10* BTDC I'm hoping that will do the trick. Anybody know where I can pick up a factory tab for this block? I've already pulled the upper plenum and replaced all the vacuum hoses from the MAP, PVC, intake etc. as well as the lines to the cooling block on the throttle body. I'm really stumped here. If it's not the timing, I can't think of anything I haven't checked. Again, the thing ran fine until the initial fail of the fuel pump. I am not generating any trouble codes at all. Any ideas?

[t65neon5]

did you replace the fuel filter and flush the fuel lines prior to the engine before starting it?....(possibile clogged injector...or injector stuck open due to foreign matter?...i.e. rust)...also...you said car sat for awhile......check ALL wiring underhood......mice & rats seem to love chewing on this stuff

[sly]

+1 clogged/sprinkling injector and check wiring/vacuum lines and PCV valve/screen/grommet. Don't forget to check the evap lines as well.

[1990LTD]

My 90 has a timing pointer held on to two of the timing cover studs. You're right in that yours should have one.

like so:




Am I correct in reading that the plugs are getting fouled with fuel and the car is misfiring?


Your ignition components are all new but do you have good spark on all 8?

[mrltd]

Have you changed the fuel filter? They get clogged easily, and especially quick when the car has sat for any period of time.

[dawg57]

Fuel filter and Lines

Yes, I did replace the fuel filter and flush the lines when I replaced the fuel pump. I don't know why I forgot to check the injectors while I had the plenum off and out ofthe way. Since I've already installed the plenum I guess one of those "clicker" tools might be the easiest way to check injector function. Thanks for reminding me.

[dawg57]

Injectors and Vacuum Lines

Forgot about the injectors for some reason during all of this . Probably too focused on the electrical side of things. Given the age of the car, that should have been an obvious consideration. Replaced all of the vacuum lines [ I thought] but found one in the fenderwell going to the evap can below the inner fender. I'm going to replace that vacuum line and use a " clicker" tool to check injector function.

[gadget73]

How old is the gas? Its not the several year old fuel is it?

[79lincolnlover]

Run some premium gas and see if there's any change.