W126..Driving along, cuts off, ABS light comes on,starts right back???????

[jay3000]

My wife was driving along, foot on the gas, and the engine cuts off.. She says the ABS light came on after the engine died, but no others.. She coasted to a stop.. Re-started it immediately, and says it ran fine the rest of the way home..

My fist thought is to replace the OVP relay, and fuse pump relay.. I know the OVP is the original one, but that wouldn't cause the engine to die, would it????

I'm not usally one to throw parts at a problem, but this one might be a little tough to duplicate the problem in the garage..

Any ideas guys???

Thanks,
Jay

[mbshop]

overvoltage relay is a very good place to start. this does
set off the abs light.

george

[jay3000]

I know the OVP is often the cause of ABS light being on, but would it cause a warm engine to die going down the road???

[mbshop]

yes. thats the power supply to control units. thats what
its there for. like when you connect jumper cables while
the key is on.

george

[Gilly]

It seems like the OVP suddenly failing can cause a stall like this, there are even bulletins out for certain vehicles which state that intermittent stalling can be caused by the OVP (although I don't believe the bulletin I have in mind covers 126 chassis). But remember that the engine can in fact run without the OVP or even without the engine control unit (not really well, but reasonably well, in what is called "fixed operating mode"). I believe it's the sudden change from running in closed loop to running in fixed operating mode which causes the stall. If your warning lights for ABS is not presently lit, the OVP is probably fine right now. If the ABS light has been lit ever since the stall, you are probab;y in fixed operating mode, which is most noticeable at a cold start.

Gilly

[jay3000]

Thanks guys.. Guess I'll try the OVP relay. After all it is 15 years old.. I wonder if it has anything to do with the SRS light coming on for several seconds, about once a week???

[MikeTangas]

The OVP shouldn't have anything to do with the SRS light.

Two things do jump to mind though - worn/dirty contacts or slip rings for one, or worn brushes in the alternator. Anytime the light is on the SRS is non-op. Voltage below 10.1V will trigger the lamp as will a sticking spring in the contact or a worn spot on the slip ring.

[jay3000]

Well.. It seems that the OVP relay has solved both the cutting off problem, AND the SRS light coming on. It's only been two days, and about 100 miles, but my wife says the SRS light was coming on several times each time she drove the car.. And, it hasn't come on since, nor has it cut off.. If anything changes, I'll post back.. But, it seems at this time that a failing OVP can cause the SRS light to come on, and cause the engine to stall.. BTW, the ABS light never came on, and it does appear to work.. At least it illumintes when you turn on the key..

Thanks folks,
Merry Christmas
Jay

[stevebfl]

The OVP is one of the top causes of stalling conditions. When I first read this post I decided not to make a statement as I evidently misread the telling intermittant symptom.

My first advice would have been there is no way it would be a OVP as it is almost impossible for a car running down the road to be severely impacted by the loss of the KE electronics (which is what happens with a defective OVP).

I haven't reread the original post but this last post equates probably the single most common condition writen about on this site: the OVP failure with ABS light coming on. The engine effect in this case is hard starting and possible stalling.

The word stalling is the key to interpreting this post. Stalling is the act of engine dieing from an idle position. My impression of the stated condition (I will go back and reread) was that the carwas driving down the road and it died. Just about an impossible condition to be caused by OVP.

Actually I couldn't wait to see if it was I that couldn't read and here it is: "My wife was driving along, foot on the gas"

While I can dream of a situation where the above statement and an OVP could be the problem. It is very unlikely and would require the car to be in severe misadjustment for it to happen. Based upon the assumption that the car is fixed, it goes to show that listening can get one into trouble. My best guess is that the car died while rolling (in the idle position) and it was mis stated that the foot was on the gas.

I mention this now not to be contrary, but to insure proper concept is attached to OVP. It seems a never ending battle.

[jay3000]

Well, Steve.. It AIN'T fixed... Your first advice would have been correct. It's not the OVP.. What's next??? The car runs beautifully otherwise.. Fuel pump make a little noise.. My wildest guess right now would be fuel pump, or relay?????? I hate just throwing parts at something..

Kind of tough to diagnose a problem that is intermittent like this .. It's also a dangerous situation that I need to figure out a solution for..

Thanks for any advice..

Jay

[johnnyg]

Jay. my 380 did it , it was the fuel pump relay.....

[stevebfl]

My experience with fuel pump relays is that they usually appear bad in a "no-start" situation. They usually don't fail once engaged.

If the problem is now happening often enough to test (I drive probably 2-500 miles a week in cars rigged to monitor an intermittant failure), I would normally hook a fuel gauge (self made) that has ten feet of hard aramid fuel line (1/8in) to system pressure and set it in my lap and drive it till the problem happened. This is probably not recommended and I do have the proper way: a pressure transducer monitored by a Fluke 87. Takes too long to hook up.

Anyway, you could try bypassing the fuel pump relay and drive, but you will never know if the event would of happened. You could monitor the fuel pump signal at the pump with a volt meter while driving. This would catch the event and verify a bad power circuit (I once had a bad fuel pump circuit that was caused by a bad ingnition module that quit sending the engine speed signal to the fuel pump relay - thus causing the relay to shut off the pump).

About the only other possibility after fuel is a crank sensor. Ignition modules and coils don't usually come and go. It is possible for the crank signal to do that especially when heat related.

The idea in diagnosing is to first establish what is missing. A dwell meter hooked to the coil will verify ignition. Remember you are looking for a complete failure not just a deficiency. That is why I eliminate dist caps (possibly rotors), plugs, wires, etc.

[jay3000]

Thanks for the input guys.. It cut off again today after only a few minutes of driving, and would not immediately start back.. I wish I had been driving it, and not my wife.. I would have been able to tell if the fuel pump was running or not. I'm leaning heavilly toward a fuel pump relay.. A little searching has revealed others with intemittent fuel pump relays.. Most have been bad solder joints.. I pulled out my relay, and it has a plastic case, and seems to be pretty well sealed up.. Perhaps I'll try to figure out a way to get inside of it...

This does not appear to be heat related.. I just need to catch it when it won't start, then I can at least know which direction to go in..

Jay

[jay3000]

And now, I'm just talking to myself .. Scraped all the silicone off the bottom of the relay, popped it open..... One of the solder connections for the relay itself was cracked big as day.. Resoldered it, and I feel confident that I have solved the cutting off issue.. If I still have it, I'LL BE BACK....

Thanks folks.. I love this forum.. If not for this forum I would have NEVER purchased this car. So far I haver managed to fix the 25 or so problems with this car without taking it anywhere.. Now if I could just figure out how to do a state inspection at home???

Jay