Engine dies at random

[Phoenix319]

I decided to give this it's own thread since it's now my major problem.

Every day it gets progressively worse. This is my daily driver so I have no other options. I had a coolant hose pop off my car a couple days ago and the day after I noticed my car started to hesitate every now and then randomly acting like it was pretending to cut the power but jolted back to normal. Now it's just completely dying out and sometimes wont even start up unless I wait 5 minutes or more in the middle of the street. I have to take the freeway every saturday so I need to fix this quick.

I checked my fuel pressure the last time it happened and it was perfect. It's definitely an electrical problem. I need diagnostics help and some experience with this sort of thing. It is most likely water damage. I replaced the fuel pump relay and the main relay with no change. It runs perfect and then just dies whenever it feels like it.

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Btw it's just the engine. The radio and lights still work when it dies.

[fiveseven808]

I'm using Tapatalk so I can't see if you've added your car to your profile, but what year is your car? The reason I ask is the early e28 based ones have a security system that if defective can cut power while driving and make it difficult if not impossible to start or restart in certain situations.

If we're talking about the later model e28 based ones, it could mean your ecu need reflowing.

[Looghis]

the thing about diagnosing the electrical systems on these cars is that its very time consuming. the only way is to check every sensor, and if those aren't at fault it's worth checking the wiring from the connectors to the ecu. its also worth opening your ecu and checking the solder joints.

i used this guide to diagnose running issues on my 635, it's extremely useful.
http://www.hiperformancestore.com/motronic.htm
i'd skip around a little and check the obvious things. see if youre getting fuel/spark

[Phoenix319]

I'm using Tapatalk so I can't see if you've added your car to your profile, but what year is your car? The reason I ask is the early e28 based ones have a security system that if defective can cut power while driving and make it difficult if not impossible to start or restart in certain situations.

If we're talking about the later model e28 based ones, it could mean your ecu need reflowing.
My car is a 1985 635csi

[wfwright2]

Hopefully not a duplicate listing.
Did you get your fuse panel or fuel pump/main relays wet with your coolant release?
It sometimes takes a little bit for the coolant to migrate enough to do damage. They are cover by rubber boots, but are open enough to allow moisture to get to them. Especially for a daily driver, it is a good idea to carry spare relays, they are one (two) of the most common operation failure mode.

[Phoenix319]

I already said I replaced the fuel pump and main relays and the problems still continues. Do you think it could be my alternator or voltage regulator? They were right under the hose that spilled.

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I'm also thinking of soldering my ECU. Anyone have instructions on this kind of thing?

[bkats]

The coolant temperature sensor may be shutting down the engine,but I'm not sure. Others can confirm if this car works like that.

Your alternator wouldn't cause the car to shut down. And if it wasn't working, you would have a dead battery pretty quickly. Waiting a few minutes certainly wouldn't make it better.

Fuel and spark systems need to be checked all the way through. Have you tested your fuel pumps? The lifter or pressure pumps could be going out. Fuel filter?

Distributor cap would be a spot to check if you had coolant flying around the engine. Possibly a damaged ignition coil, but I doubt it.

[alpinacsi]

Swap the motronic DME with a known good one or try to refow the solder joints on yours. You should have a 059 DME and the procedure has been detailed here on the site: try searching or maybe someone here will have the info handy.

[Looghis]

i reflowed all the joints in my ecu, its pretty straight forward. use a low wattage iron and be very careful. the ecu is located under the glove box's top panel.

[alpinacsi]

http://www.bimmerforums.com/forum/showthread.php?2128462-When-Motoronics-go-bad&highlight=ecu+solder

[Phoenix319]

I broke down 4 times on the way to work today but luckily I work for an auto parts warehouse so I was able to get a new Huco Voltage Regulator instantly. The drive home I had no problems. I'll update if any new developments occur.

[Phoenix319]

OK so it was running fine for a while but now it's starting to hesitate again and I fear it will soon start stalling. Any recommendations? I know it's from some type of water damage because this exact same thing happened to a friend from driving through a huge puddle and he ended up selling it after replacing the distributor, alternator etc.

[conez0]

You said you checked the fuel pressure and its good when this happens. So to confirm, you read ~43 PSi (43.5 +/- 0.9 per Bentley manual) WHEN you are cranking and it still DOESNT start?

Just want to confirm because I had a problem that matches your symptoms perfectly and it ended up being the in-tank fuel pump.


Follow through the troubleshooting steps in the Hiperformance Motronic Writeup to make sure the entire fuel injection system is working properly. Print it out and keep some wire and a multimeter in your car so you can troubleshoot next time you break down. An intermittent electrical problem is hard to track down but with the motronic writeup, wiring diagrams, and proper tools you should be able to do it, the tough part will be catching it when it rears its head.

[Phoenix319]

You said you checked the fuel pressure and its good when this happens. So to confirm, you read ~43 PSi (43.5 +/- 0.9 per Bentley manual) WHEN you are cranking and it still DOESNT start?

Just want to confirm because I had a problem that matches your symptoms perfectly and it ended up being the in-tank fuel pump.


Follow through the troubleshooting steps in the Hiperformance Motronic Writeup to make sure the entire fuel injection system is working properly. Print it out and keep some wire and a multimeter in your car so you can troubleshoot next time you break down. An intermittent electrical problem is hard to track down but with the motronic writeup, wiring diagrams, and proper tools you should be able to do it, the tough part will be catching it when it rears its head.
Yes I did multiple times. I have a fuel pressure gauge installed right under the hood and it read perfect 43 psi. It's some kind of ignition problem. I tested the coil and it's fine, the distributor cap is clean, the spark plugs or OK, and wires are brand new bosch ones I just installed 3 months ago. My crankshaft position sensor and speed sensor are very old and have cracked brittle plastic ends that are almost completely fallen apart. I ordered some new ones and a Graf water pump with new belts from FCPEuro since the water pump is on clearance for 22 bucks. I'll let you know if that works when I get them.

[tgmedin]

Heed the warnings about old ECU's on these cars. I fought the same type of gremlins for over a year before finally biting the bullet and getting a reman ECU from Programa. Yes you can reflow the joints with some success but you you still have a 30 year old ECU. The Programa unit is thoroughly tested and comes with a warranty to boot.

My new ECU cost me less than my first flat bed tow bill! I had all the classic symptoms discussed here and everything else checked out OK. Once I replaced the ECU. now over a year ago, all the problems have disappeared and I can drive my car without worry once again. Do yourself a favor and invest in the reman unit, you won't regret it.

Good Luck,

Tom in VA

[DesktopDave]

Yes I did multiple times. I have a fuel pressure gauge installed right under the hood and it read perfect 43 psi. It's some kind of ignition problem. I tested the coil and it's fine, the distributor cap is clean, the spark plugs or OK, and wires are brand new bosch ones I just installed 3 months ago. My crankshaft position sensor and speed sensor are very old and have cracked brittle plastic ends that are almost completely fallen apart.

Sorry you're still having troubles. Sounds like you've really gone through all this, so forgive me if I'm suggesting obvious things...I've had more than a few early Motronic that ended up being very simple problems that I was over-thinking. Here's a few suggestions:



Did you verify that the coolant temp sensor didn't have a resistor soldered in-line? I've had more than one BMW with a good CLT sensor...but a wire fault from a dealer-installed resistor spliced into the CLT harness. They're usually hiding in the plug boot, it was a fix for smoothing out cold starts.
Did you ohm out all the spark plug wires & boots? Check for cracked plug boots? I had a coil HT lead with a weak connection once that caused instant shutdowns. It was very hard to solve since it only happened when the plug wire was bent a certain way.
Loose connectors on the in-tank lift pump will starve the pressure pump. I had one that would push out of the plug internally, so it looked good but made an intermittent connection.
Have you swapped in a known-good coil? They do tend to fail at higher temps. They are very hard to test hot since it takes a while to remove the primary coil wires to get an accurate reading. I've heard some buddies pull them off the car completey & toss them in the oven at low temp (~200degF) to test resistance.
Ditto the resistance on the speed & position sensors in the bellhousing. Test them when the car is warm for proper resistance (IIRC ~1K Ohm on the sender pins , >300KOhm on the shielding pins). Even obviously new ones can be bad, and they're critical to the car's running.
While you're replacing the position sensor on the bellhousing, manually rotate the flywheel/flexplate to visually verify the reluctor pin is still welded on. I've heard of a few cars with broken pins that ran badly or not at all.
You've never had problems with the ignition key switch, nor the 'code' box under the driver's kick panel? Both can immediately and randomly shut the car down.

[RSheiman]

Here's a long shot. I had a 320i that did this. It turned out to be a crack in the copper wiring inside the distributor. Crack was not visible to the eye but swapped and never happened again. This was per some old-time certified BMW mechanic.

[Phoenix319]

Alright I feel dumb now. I should have checked this as one of the first things but it slipped my mind. It was the Throttle Position Sensor. It runs a lot better unplugged and rarely stalls. My new one is coming in today so I'll post back after work when I replace it.