ESS Background

[baker2acre]

Ok Guys, hopefully this will be a quicky for you fuel oil geniuses!

Had some stalling trouble and I've been reading and testing as time and funds allow, which sadly these days both are short!!

Over the past several odd months of Saturdays I've checked grounds, charged batteries, cleaned cables, checked lift pump, swapped out FSD, even bought an ignition switch/harness.... still the stalling (expensive harness so I returned it!). Sometimes it runs fine for a while. Other times it stalls right off start up and then doesn't restart. Never a big drawn out "death scene" or loss of power. Just there and then gone!

Which leads me to my newest test... the ESS (engine shutoff solenoid). Did the "click" test and could hear it click with my wife at the key switch but had read something about low or intermittent voltage. So, jumpered it the other day direct from one of the batteries and it ran like a champ and drove all over the place!!! :D Popped the jumpers off (the solenoid, not me :p) and hooked it back into it's connector. Started right up.... and died!!! :mad: Fine, buy a new ESS... but what if that's not the REAL problem just a symptom?? That $100 could have gone to fixing it and not replacing it. I'm cheap!!

My question.... where does the ESS get it's direct power? From the ignition switch?? Through the FSD? A "safety" sensor like the oil pressure sensor? Or does it go through a comity of "hand washers" before reaching the ESS?? (If it's a the "hand washers," I'm installing an on/off toggle with a monkey to turn it off in case of crash!! or is that the same thing?)

Thanks in advance, Les

[racer55]

Ground for the FSO is from pins C15 and D15 @ the ECM if I read the manual correctly.
There is also a 20a ECM-1 fuse that powers the FSO and the PMD in the underhood fuse block.
And then there is the wiring between those 2 points.

This info taken from a 2001 manual.

[JohnC]

Yup, the power to the solenoid is pretty straight, from a fuse. The ground is controlled by the ECM. DO NO BYPASS this control! If your Fuel Solenoid or FSD fails you could have a runaway and the ESS is the only thing standing between your engine and total destruction.

From your troubleshooting, I'd look first at the connector...

(Later) Reread your post. Did you put a jumper wire from the solenoid to ground? If so, you have eliminated ECM control of the solenoid. The ECM may be causing the solenoid to drop out. If so, it's most likely because the ECM sees a problem with the fuel solenoid.

[More Power]

For years, Stanadyne claimed the PCM was the culprit for many of the stalling problems that resulted in a pump/PMD change.

For years, I considered their claim to be simply an attempt to avoid responsibility.

However, it is possible as is pointed out above..... That said, I don't remember a case where it was, but I have heard of several instances where a PCM was replaced at the owner's expense, but it didn't help. ;)

Jim

[baker2acre]

Thanks guys!

That answers my questions a bit.

JohnC, yes I ran a hot lead in and a ground out completely eliminating all controls to the shutoff solenoid. Were you referring to the ECM harness connector?? You said the ECM/PCM may be dropping the solenoid because it sees a problem.... can you explain a little more?

Thanks Jim, the PCM was a question mark for me but I wasn't sure if there were other "influences" in the ESS's controls. Not saying that the ESS is creating the stalling, but my one test gave GOOD results and I want to know why!! Does Stanadyne still point to the PCM or have the softened with evidence over the years?

In theory then (not practice for safety reasons as JohnC pointed out), if the PCM/ECM was giving intermittent grounding or just opening and closing the circuit for giggles.... could that process be singled out of the testing by jumping a good ground to the solenoid?? Ergo if "known" ground applied makes no difference, one could rule out PCM interference pointing the finger back towards the "hot" side (fuse, harness, ignition)?? Is there another way to check this side of the controls other than replacement?

Thanks again!

[JohnC]

I was suggesting the PCM is dropping the solenoid because it sees a problem elsewhere, to prevent a runaway. Whether the problem is real or just perceived is another question.

One thing you can try, if you have a scanner, is to monitor Fuel Solenoid closure time. If it starts to fluctuate right before the stall, that's your problem.

[baker2acre]

Thanks JohnC... I see what you're saying now.

[Lug]

Had a similar problem that finally went away when I found the loose connection on the firewall hot battery buss. The p.c.m. power wire is one of the orange fusable link and the connection was loose enough that I was getting a voltage drop to the p.c.m. Tightened it up and it ran good until the lift pump quit. I wasn't getting sufficient voltage to the p.m.d. during start. This is on a 94 'burb.
Justin