I have an 1986E w/160K according to the odeter.

I have been trying to find the source of an engine miss for a while now, and after much good advice I have received here, here are the results:

Compression check was ok with all cylinders within 5 psi of each other...150-155psi.

All plugs are new and were removed to do the compression check and all but one were good with a tan/grayish electrode. My #5 plug was a little on the wet side..looked more like fuel and no oil fouling.

All new wires. Also checked resistance while doing compression check...all were under 9k ohms.

Did the fuel pressure chech with the key on=no start I had a pressure of 38-40psi. Engine running had the same pressure...disconnected vacuum and jumped up to 46-47psi. But it would leak dow to 20psi within about 3-4 minutes.

Switched out MAF sensor with a good used one with no change.

Tested the TPS and was out of specs. Before ajustment, closed throttle produced .27 volts and WOT was right at 3.27volts. Adjusted it to the closed position is now .48volts and WOT is 3.52volts. I don't know if there is an adjustment on the gas pedal or not, but I pushed the little lever on the TPS to WOT and the signal output was 4.89volts..and the signal voltage from the gray wire is correct at 5.02volts...so I believe that the TPS is functioning correctly.

I am not so sure about the distributor or coil?? I have an odd whine or 'roar' from that immediate area...it almost sounds like a tranny pump whine or power steering pump, but it does it all the time--hot, cold. I didnt know if distributors can just wear out, the sound reminds me of a dried out bushing.

Also looks like I have a leaking injector from the lightly wet plug and the fuel pressure leakdown test. Anyone have any additional ideas?

 

I also don't have any stored codes and the check engine light doesn't come on while driving. Everything seems to be working fine except for the low rpm miss. Does this engine batch fire the injectors?

Will a distributor just "wear out" after say 160k?

 

Yes it can.

Remove the distributor cap and try turning the rotor by back and forth.

There shouldn't be much play. If there is then it's possible the distributor gear is worn, or the cam gear.

If it seems to be ok then the other possibility is the timing chain is stretched. Either way, put a timing light on it and start it up and see if the timing mark on the crank pulley looks steady and isn't jumping around.

If it is steady then I would suspect either the leaking injector is causing the misfire or possibly the coil is breaking down.

 

Thanks. I was thinking of that as well. I checked that when I replaced the cap, rotor, plugs, and wires...and I do remember excessive play, but I figured it might of had some kind of mechanical advance so I didn't give it too much thought-and the timing was jumping around then. Yesterday when I checked the timing again it was steady. With the est disconnected though I had the base timing at 6 degrees, but would jump up to 12 at around 1000rpm. Coincidence?

 

Turn off your underhood lights and at night in a dark place, idle engine and look along each plug wire for sparks. If you have broken or missing plug wire looms, replace them. Plug wires should not touch metal. All plug wires have microscopic pinholes in them which will spark through to ground causing a miss. The spark is supposed to occur at the plug gap, nowhere else!

 

The ignition module (yes the Module - inside the cap) is supposed to advance the timing by a set amount at "around" 400 rpm. Normally you would never see this advance happen since normally the motor would never idle or run that slow. The Amount of this advance ought to be 5-6 degrees.

This may be the jump in advance you see at 1000 rpm (est bypass wire disconnected). If so it's a symptom of a dying or faulty module to be doing that advance so late.

There is No sort of vacuum or mechanical advance in this distributor, at all. Or Shouldn't be...

With 160K on the motor it's All going to be "loose". The Timing chain and gears are probably scary, the distributor drive gear (on the distributor shaft AND on the cam) are likely well worn also. It all adds up to a lot of "wander" in the timing.

 

Yes.

If you haven't already done so, get a Volt/Ohm meter and check the resistance of your injectors. Perform test cold and hot. If less than 10 ohms, you have bad/failing injector(s). (They are supposed to read 16 ohms).

Your leaking injector leads me to believe this may be your problem.

 

 

I was taking apart the top half of the engine in preparation to put on a new edelbrock high flow intake, slp runners and plenum...all port matched, when I discovered my cold start injector seemed to be leaking. The engine hasnt been started in over a week, but the plenum had a strong gas odor and the CSI appeared to be wet with fuel. All other injectors were dry...not to mention the egr valve doesnt work, wouldnt hold a vacuum, which doesnt help things.
So if the egr isnt holding vacuum, that means it's been in the closed position this whole time plus a vacuum leak. Beginning to wonder if I even need the egr to start with....