Originally Posted by gazfish

Have your LH and EZF ECU’s ever been rebuilt. If they are original it might be time for a refresh?

Originally Posted by Mrmerlin

did you use a Bosch CPS or the less expensive version?

Originally Posted by The Forgotten On

How old is your temp II sensor? It should be replaced with every timing belt as when they fail they can cause all kinds of issues.

The battery terminals being loose as mentioned above is what caused my issues on my 89. Check those too as they're easy to get at.

Originally Posted by dr bob

The CPS is related to lots of the symptoms you mention. When the engine threatens to stall, does the tach go to zero or just fall with the RPM drop. If the former, CPS is a suspect. The CPS via the tach signal sent to the injection controller is one thing that tells the fuel pump to run.

How is the rest of the top of engine wiring? Did you clean and secure the injection system ground point at the top rear by the CPS? Then on to the injection wiring, where a fault (short) in any injector's wiring will cause all to stop working. If the wiring for any of those is similar to what you report for your CPS connector, you may decide to get new connectors for all (injectors and CPS) and have a soldering-iron festival event under the hood. I think Roger stocks all the correct connector shells and pins. Do the throttle switch connector and look hard at the MAF connector at the same time; all live in the same environment and any could cause the erratic symptoms you describe.

How are the plug wires? Those usually show up as a rough idle and miss under load. Coil wire plugged in completely? You can use an Ohm meter to check the wires for open, but checking for "leaks" to ground takes a little more work. Easy first test is with a spray bottle and tap water, fogging the water over a running engine in the dark. Little lightning flashes tell you where spark energy is leaking to ground. I have a vintage CRT oscilloscope dedicated to automotive diagnosis. I think it still works... Anyway, it's handy to finding ignition issues, with just a little bit of creative connecting and probing. Replacing every ignition piece is cheaper than buying a decent 'scope though. Borrow one or find one used if you can rather than buy new.

Originally Posted by dr bob

In industrial troubleshooting, I use some mini telltale relays to detect even a momentary drop-out of a signal. I don't have a diagram handy to share, but the description may be enough for you. I look for a mini relay that includes an LED (or neon for AC circuits) indicator, else get to fit a suitable bulb. You can use a 194 easily for 12V and not mess with LED's and resistors. One external connection to one of the coil connections. The other coil connection to one side of an "A" (normally open) relay contact. A second external connection to the opposing relay contact. Add a monetary-close pushbutton in parallel with the relay contact, and put the bulb in parallel with the coil connections. Connect the two leads to the circuit under test, with the circuit active (powered). Press the button, the relay closes and the indicator light goes on. The relay will stay closed and the light stays lit so long as power stays on. If it drops out even momentarily, the relay opens and the light goes out, stays out until the circuit is powered again .and. you push the button.

The 15 circuit from the ignition switch shows up on certain fuses, so a fuse tap might be used to make a test connection there for your telltale. The other lead from the telltale goes to chassis ground. The fuse diagram for your model year will tell you which fuses get 15 (on with key in run or start positions), which get 30 (always on) and which get X (on with key in run position only). Certain circuits may get X power via the X-bus relay, depending on year. The fuse diagram will guide you.


HTH!

Originally Posted by Randy V

If it tends to occur after running awhile it may be heat related affecting the EZK or LH computers.

I had this problem.

Try removing the panel and foam that cover trhose two computers to give additional cooling. If the problem goes away then you know it is one of those.

This was my problem and how it was fixed:

https://rennlist.com/forums/928-foru...ermittent.html

Originally Posted by bureau13

Interesting! I have not been able to discern any sort of correlation with time running, unfortunately. Yesterday I did some testing, I wanted to see if I could tell when the tach dropped, to indicate if it was CPS vs just falling with RPMs. The first occurrence was within five seconds of startup, so quick I wasn't expecting it. It didn't happen again in the driveway, so I took it for a spin and drove around for about fifteen minutes, but the only time it happened, I was turning and so had my eyes on the road. It didn't happen again until I got home and was idling again. In that case it's really hard to tell because the engine spins down from idle quickly...but I THINK it did not drop, then die. So for what that's worth, it indicated NOT a CPS problem (take that with a huge giant mountain of salt of course). But regarding some sort of heat soak issue, it really doesn't seem to be that. Also, coincidentally, I have everything pulled back from the CE panel and EZF/LH because I was inspecting for burnt wires, etc.

Originally Posted by SteveG

The big guns have spoken; if it's still broken . . ., ignition switch?

Originally Posted by dr bob

Make the little telltale-relay I described, and connect it to a circuit-15 fuse and see if it's the ignition switch. Just looked in my boxes-of-things and don't have a momentary-close pushbutton, or I'd make one and send it to you.

A few handy diagnostic pieces like this will pay for themselves in minutes, just in the time saved hunting for erratics. Save yourself the agony and frustration of throwing parts at it.

You can back into a diagnosis by bypassing the ignition switch completely at the CE panel. Add a 12ga jumper between the 30 bus (incoming primary connections from the jump post) to bus 15, through a high-current-capable switch. Turning the switch on puts the switch in parallel with the ignition switch 15 contacts. You can "inject" the jumper current at the top of fuse position 7 (seat heater) with the fuse removed. If the car drives normally with no dropouts while that switch is closed, the ignition switch is your prime suspect. Warning: The jumper will be at full battery potential with no short-circuit protection. A fault-to-ground risks the primary wiring in KS-1 from jump post to CE panel. Use Appropriate Precautions!



For those playing along at home, fuse numbers I shared are correct for the OP's 1986 car, per the wiring and fuse diagrams. Those may or may not be correct for you not-a-1986 car.