Those are good pressures, especially with the upgraded fuel spider. Forgive me if I cover some old ground and I know that you have already done some of these. Misfires can have so many causes that it can be a real challenge to find the cause, especially in an older engine.

First is codes, sensor values, fuel trims and O2 sensors

Next up is the ignition system. Always use AC Delco for ignition parts and fuel pumps BTW. CMP retard in spec, good cap, rotor, wires and plugs. Mist in the dark to rule out crossfire. Inspect distr cap for same. Measure wires for proper resistance, check all boots on tights, check wire order. Check for 1" of strong blue spark with a good cadence. You can do a drop cylinder test by pulling and grounding wires while at idle.

Then fuel pressure and leak down.

Then fuel injector balance which fires each injector and looks for even fuel delivery

Crank sensor relearn if you changed anything so that you have the correct misfire cylinder.

Vacuum leaks

Powers and grounds

Last we have mechanical problems (valves, rings, bearings, pistons, cam lobes, exhaust restrictions, etc. First up would be a std compression test with leak down. If that shows nothing then a dynamic compression test which shows the breathing and compression of each cylinder while running.

There are more esoteric tests requiring a scope that can look at injector firing, ignition waveforms etc that a high end shop would do but that's beyond the capability of most here so I don't usually get into this stuff.

You can audit against this list for completed items and then let me know where you want to go next. You might have a dynamic compression test in your future (something that Les brought to the party).

George

 

Slightly cooler 🤬 weather today so did the compression test, all plugs removed, fuel/fire disabled, pressure was from 160 to 175 so those are good. Did the water mist test tonight but saw nothing. Did remove the spyder connector and found one wire was sitting on one of the plastic post so it was being crushed/ flattened when the cover was on, I smoothed it out and don’t believe it was broke. Going to drive about 80 mile round trip tomorrow to see how it goes.

 

So you had one injector not firing?


George

 

I don’t think it was not firing, again today it ran great for about 25 minutes then the SES light goes to flashing but not on steady. I can tell by the rpm’s full power is not there, mileage sucks at 16 mpg. Usual code po300. Today cylinder #5 added it’s self, misfires as high as #2. I have noticed the higher the rpm’s the higher the misfires, I assume that’s to be expected. Can a HF noid test kit be connected to the spyder system? If so I guess I need to go that route next. I did pull # 1/5 plug while it was running and you could definitely tell when each one was pulled. You had mentioned the O2 sensors, left side is fairly new, replaced due to being damaged when I had the trans rebuilt. #3 was pulled an cleaned two weeks ago, #2 has not been touched. What data do you need to confirm if they are working completely?

 

There are a few ways to test the injectors:

1) Are you getting firing pulses from the PCM (ground side control) to each injector. The noid light replaces the injector load and gives a visual confirmation

2) Are the injector coils with spec (11-14 ohms each, no more than 3 ohm variation).

3) Do they all inject the same amount of fuel when fired (pulse box, watch the pressure drop)

4) Watch for the pintle hump on a scope (not for most diy mechanics)

O2 sensors:

1) Graph both upsteam sensors. aprox 1 hz switching at idle from 0.15v to 0.85v (mostly) with about a 100ms rise and fall time.

2) You can also force lean or rich and watch the reaction time

3) Downstream does not track upstream after everything warms up

4) Heaters and heater circuit are working

5) One quick check is to swap sensors to see of the problem follows but now you have both banks involved so this probably wont tell you much.

6) Do they peg rich under full throttle acceleration.


George

 

Have a scheduled day first week of August at a highly recommended shop downtown. Talked with the owner about the misfires an all the parts I’ve replaced. He have a level 2 type machine that can read tons of data but more importantly knows what the data means. Hopefully this way I can quickly get to the exact problem and fix it. I’ll let you know what I find out.

 

Good luck, keep us posted.


George

 

While replacing the distributor I discovered a large amount of chain slack so I’m in the middle of R2 it now. Having a hard time finding a good pic of corrrectly lined up sprockets.

 

Here you go





;

George

 

Thanks, good information. The large cam sprocket had an arrow at the 12:00 position, crank sprocket was at 12:00 also. I have #1 at TDC an the distributor rotor is pointing at the #6 mark on the distributor. Am I supposed to have #4 at TDC for this chain replacement? Do I install new chain an sprockets same as the old set?