GM Module fuses

[The Ry Guy]

Trying to find what circuits are connected to the 4, 10 amp fuses on the GM Module on my 1993 400E, and I'm striking out looking at the wiring diagrams I have. I found the 3rd fuse down from the top blown, and am trying to figure out which circuit it's on, so I can determine the cause of it blowing.

I found this while trying to diagnose a problem with my ASR. I drove the car for a quite a while in limp mode and other than the reduced throttle (which I know is normal for limp mode) it drove fine. The ASR diagnosis deserves it's own thread, which I haven't started yet.

 

[gsxr]

The schematics are in the Electrical Troubleshooting portion of the FSM. You have to scroll down to the individual diagrams for "Engine 119 LH-SFI". There may not be a single diagram that shows everything related to the GM, it may be broken up into different schematics:

24 Electrical Troubleshooting

Limp mode is almost always related to the ETA or E-GAS module. Search the forum for troubleshooting tips. First thing to do is pull fault codes from the E-GAS and see which codes return after you get limp mode again.

 

[gsxr]

This PDF file shows what systems are on each fuse:

https://www.w124performance.com/docs/mb/M119/BasicModule_functions.pdf

 

[The Ry Guy]

Thank you GSXR for the replies. I replaced the 10 amp fuse that was blown, and the car ran a lot better immediately. It was loading up, stalling and not restarting after attempting diagnosis of the ASR problem last week, and I think it was because of that blown fuse.

I let the car warm up and took it for a drive. Everything was back to normal, car ran strong, no limp mode or ASR light. Found a large patch of ice and both the ABS and ASR functioned as they should have. Only thing I noticed was a surging idle in park when fully warmed up, but no ASR light.

Pulled the car in the shop to read and clear codes on all the modules. I just have a little homemade blink tester made with some probes, an LED and some alligator clips. There were quite a few codes, so I cleared them all (after writing down what they were).

Went to back the car out and the ASR light was back on with limp mode. Well, crap. So I pull it back in and check for codes. Only thing that came back right away was code #2 on pin #7. Wish I had an actual scan tool, because there's about 14 things that can trigger that code!
Wish I had a scan tool to narrow those choices down!

I can rule out the switch on the accelerator pedal, because it's brand new and tested fine. The old one was likely fine, but I didn't know that there's about 1k of internal resistance in the switch. My meters continuity mode doesn't go that high, so it thought it was open! Switching to resistance measurement solved that puzzle.

After retrieving that code, I decided to try and get the car home (car was at my parents for about two weeks since it stalled and left me stranded) since it has stopped stalling on me. Made a stop for gas, and when I restarted the car, the ASR light was off and no more limp mode. Drove fine the rest of the 15 miles home.

I want to investigate the causes for code 2, but not quite sure how to approach that. Are there resistance or voltage drop values I can use on those components? I found instructions for using a breakout box to measure values, but I don't have one of those.

Other things to note are that my engine wiring harness was replaced in 2019 with a new Delphi one, but I am unsure of the age of the ETA. I did check the wiring inside the ETA when I got the car in 2019, and It looked ok then, so I decided to go with it.

Should I start a new thread for the ASR diagnosis?

 

[gsxr]

If the ETA is original and never rebuilt, it is highly suspect as the cause of intermittent limp mode. Digital codes from a scanner would help prove this but if you don't have access to an SDS with HHT-Win, it may be cheaper to get the ETA rebuilt by Victor in NY.

That said, I'm not certain the blown fuse was the cause of the poor running. Now that it's running (more) normally, you could try a test to confirm: At operating temp, pull that fuse and see if it immediately runs poorly, then re-install the fuse and see if it is "cured". If so, great, that confirms the fuse was the root cause. If not... you may also have secondary ignition problems, which typically cause exactly what you describe (loading up, stalling and not restarting).

Decent chance you are dealing with two completely separate issues here (ETA & limp mode, and also ignition / poor running).

 

[The Ry Guy]

I think I'll try to parse out what might be causing the intermittent limp mode, before sending the ETA off. I have another ETA that I pulled from a W140 in the junkyard some years ago, and I've been probing the wires on it to see what does what, trying to cross reference that with the wiring diagram. Other than the clutch coil and motor, I haven't been able to determine what wires are the TPS or switch. I did conclude that on both my car and my spare ETA that the clutch coil and motor work by applying 12 volts to those circuits.

I'll try the fuse pull on my GM and see what that does. I initially thought secondary ignition, even though those components are only 2 years old with about 30,000 miles on them. I did pull the caps, and didn't see any moisture or oil mist, (new cam seals when I did the caps and rotors) so I scraped what little junk was on the terminals off, reassembled, and no change to the stalling. Only when I put a good fuse in did that go away.

It's pretty cold here this week, it may take me a while to get back to this, but I will update this thread when I figure something out.

 

[gsxr]

You can perform basic testing on a spare ETA if you have SDS to view live data, otherwise it's easier to just swap in the spare ETA (takes about an hour, if all goes smoothly, and the rubber hoses & connectors aren't fossilized).

If the misfiring / no-start condition occurs roughly 10-20 mins after a cold start, it's even more likely you are dealing with secondary ignition. With new cam seals, also make sure the cam solenoids are not leaking engine oil along the bottom edge of the caps. Adding the vent slots as shown in the thread below will help eliminate condensation / moisture:

FYI - Essential M119 Ignition "Tune Up" mods [Distributor cap vent / slot] | M119 Engine

Hi all, I have been meaning to address this on my little used 500E for years.... it is a problem I myself recognised about 5 years ago when I first looked at an m119 distributer cap..... Compare to any other distributor cap of the era such as an m104 and you will see there are NO ventilation...

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