528e Starts then immediately dies out

[MattyL]

Hi all, I’m new to the forums and e28 community. I recently purchased an ‘84 528e, it has been running and driving perfectly fine up until earlier this week. It’s been having issues starting: First it would crank endlessly and not fire up at all, even with starting fluid. I figured it was because I did not have enough fuel in the tank, I put more gas in and it was working fine the past 2 days. Today I drove it to and from work with no problems, I went to drive it tonight however and now it will start up and immediately die out. I’m suspecting it’s a fuel related issue, the in-tank pump is definitely dead but that shouldn’t cause this issue. I’m curious as to where to start with diagnosing? I’ve already swapped the horn relay in for the fuel pump relay and that hasn’t fixed the issue. Any suggestions would be greatly appreciated before I start just buying parts I may not need. 

[1st 5er]

Got more than 1/4 tank of gas?
Intank pump is absolutely necessary below that point.

There are 2 reference sensors on the bell housing with connections at the rear of the head. 1st is for start signal and 2nd is for run signal. If 1st fails then no start. If 2nd fails then no run. Bentley has the test specs.

[Shawn D.]

I see this is your first post welcome! Please read and heed the Forum and Tech FAQ sections.

Starting and immediately dying could be an AFM issue. If it does not sense any air is passing through, the ECU will shut off fuel. Make sure the AFM is properly connected and then run through the tests shown in the Bentley.

[Mike W.]

Got more than 1/4 tank of gas?
Intank pump is absolutely necessary below that point.
.

That has not been my experience. Being the cheap SOB I am, I never bothered to replace the pre pump on my E28, and yes, verified it was dead. I ran it into the warning light dozens of times in the 155K I owned it. I think rated capacity of the fuel tank is 16.8. I routinely put 14 gallons in and a couple of times running on fumes got 15 and a fraction in. With one fuel pump it would start cutting out at high RPM, say 5500+ at full throttle, if I was below a quarter of a tank. Normal driving I never noticed. With other pumps it pulled just fine to redline below a quarter of a tank, or at least 5800-6000 and why bother it was past peak at that point, I needed to shift.

[1st 5er]

Got more than 1/4 tank of gas?
Intank pump is absolutely necessary below that point.
.

That has not been my experience. Being the cheap SOB I am, I never bothered to replace the pre pump on my E28, and yes, verified it was dead. I ran it into the warning light dozens of times in the 155K I owned it. I think rated capacity of the fuel tank is 16.8. I routinely put 14 gallons in and a couple of times running on fumes got 15 and a fraction in. With one fuel pump it would start cutting out at high RPM, say 5500+ at full throttle, if I was below a quarter of a tank. Normal driving I never noticed. With other pumps it pulled just fine to redline below a quarter of a tank, or at least 5800-6000 and why bother it was past peak at that point, I needed to shift.

Maybe "absolutely" was to strong a term, but the several failed ones I experienced had me coasting into gas stations well before the low level light came on.

[jimoreno]

That has not been my experience. Being the cheap SOB I am, I never bothered to replace the pre pump on my E28, and yes, verified it was dead. I ran it into the warning light dozens of times in the 155K I owned it. I think rated capacity of the fuel tank is 16.8. I routinely put 14 gallons in and a couple of times running on fumes got 15 and a fraction in. With one fuel pump it would start cutting out at high RPM, say 5500+ at full throttle, if I was below a quarter of a tank. Normal driving I never noticed. With other pumps it pulled just fine to redline below a quarter of a tank, or at least 5800-6000 and why bother it was past peak at that point, I needed to shift.

Maybe "absolutely" was to strong a term, but the several failed ones I experienced had me coasting into gas stations well before the low level light came on.

Yep, just happened to me coming back fro the Vintage in my '86 535i. Classic "out of gas" sputtering, took the off ramp of I-95 (already in Florida) and added two gallons of gas (After the walk of shame) and restarted on the 2nd try. Filled it up and finish the rest of the trip making sure it never got near the 1/4 of the tank again. Hoping to do the single in tank pump installation this weekend. It's the original pump with 250K miles (was going to replace it but when I saw the $600 plus price tag I quickly changed my mind).

[MattyL]

Sorry I haven’t had a chance to reply in here until now. Originally I suspected it was just low on gas, had just over 1/4 tank so I filled it up and it was fine for about a day. Started having issues again. I checked the AFM, unplugged it and it wouldn’t start, plugged back in and wouldn’t start. Same thing for the cold start injector. For some reason my FP relay is gone, I had swapped the horn relay in and it was working for a time. Taking the horn relay back out and it fired right up. The high pressure pump sounds a bit noisy and strained so I’m still thinking that is my main problem. Thank you all for the suggestions, next I’ll check the reference and crank sensors to see if they’re faulty. I ordered some parts preemptively: HP fuel pump and filter, new spark plugs, injector rebuild kit, valve cover gasket, and some other small things to take care of some much needed maintenance. I drove the car twice yesterday and both times it started up fine, it idles normally and drives normally as well.

[MattyL]

UPDATE

Last weekend I ended up replacing the high pressure fuel pump and filter, along with the spark plugs. This seemed to drastically improve my issue but something is still off. The car starts fine every morning, it fires up first try to idles normally. After sitting in the parking lot at work however, it takes me anywhere between 5-15 minutes of cranking it before it fires up. This seems to happen every time I drive it somewhere and let it sit. It’s worth noting that when I spray starting fluid into the intake, it will fire up and run until the fluid is burned off. I’m still thinking there is something going on with fuel delivery.

The pressure regulator was my next culprit to check and it seems to be functioning normally. There is an air leak of sorts under the intake manifold, based on the whistling noise it makes it sounds like air is escaping rather than being sucked in. Not sure if this would cause the issue I’m experiencing. It’s also worth noting that with the “crank, no-start” condition, the tach seems to jump all over the place. Could this be indicative of a faulty sensor which would cause a no start? I also have an injector rebuild kit to throw on there as well, I’m not certain if they’re leaking and flooding my engine. I’m just curious as to what I should check next, this issue isn’t preventing me from driving the car but it is rather annoying and something I’d like to solve.

[1st 5er]

Faulty CTS, coolant temp sensor, can allow for good cold starts but slow or no hot start (cylinders flood with gas as computer thinks the car is still in cold start condition). 

Happened in a buddy's E28 ///M5, turned out the harness connector at the CTS wasn't plugged in securely. 

[MattyL]

Gotcha I’ll have to check that then

[MattyL]

Car broke down on Sunday when I was leaving work. Would just crank but this time I could not get it running at all. I had my buddy listen for the fuel pump while it was cranking and nothing, I know they are supposed to make a low humming noise but not sure how loud. The main relay also seemed to be bad, just replaced it thinking that might’ve been causing my issue and nope, same thing. It does have spark, so I think that rules out any sensor/dme issues, it seems just that the pump itself will not run.

I did try to check fuel pressure, in attempting to disconnect my feed line, I broke the plastic “t” piece it was connected to and fuel came pouring out. This is after I tried starting the car after it had been sitting for 4 days. I’m thinking there’s something with the fuel pump circuit preventing it from running. I’ll look at the injectors this weekend as that’d be my next guess, but is there anything else that could prevent the fuel pump from getting power before I start digging into wiring?

[jimoreno]

Have you tried the OBC relay bypass? 

[MattyL]

No I haven’t I don’t think I’ve heard of that to be honest

[jimoreno]

If your car has the OBC with the "code" function there's a relay that triggers the main relay. It can fail open and create starting issues. Search for "OBC bypass" and you'll find the instructions bypass it. 

[MattyL]

Gotcha I will check that out tomorrow then, I believe mine does have the “code” function and the obc itself doesn’t work

[MattyL]

Discovered something extremely weird today: before I went to splice the wires I got a multimeter on both of the fuel pumps to verify once more that they were not being powered. For giggles we unplugged the level sensor in the tank to check voltage.

before unplugging, neither pump had power. After unplugging, both read about 12v, and the car started right up. There’s still that tear in the t piece I have to replace, so on restarting it just sprayed fuel out rather than into the fuel rail. But the pumps get power it seems with the level sensor unplugged. 

It makes absolutely no sense to me and cannot wrap my head around how that would happen, does anyone have any ideas? I’m leaning towards a wiring issue

[1st 5er]

Discovered something extremely weird today: before I went to splice the wires I got a multimeter on both of the fuel pumps to verify once more that they were not being powered. For giggles we unplugged the level sensor in the tank to check voltage.

before unplugging, neither pump had power. After unplugging, both read about 12v, and the car started right up. There’s still that tear in the t piece I have to replace, so on restarting it just sprayed fuel out rather than into the fuel rail. But the pumps get power it seems with the level sensor unplugged. 

It makes absolutely no sense to me and cannot wrap my head around how that would happen, does anyone have any ideas? I’m leaning towards a wiring issue

Did you plug it back in and try again?

[MattyL]

I did not, it was late at night and I was spraying gas everywhere so I stopped messing with it. I’m wrapping that fitting in electrical tape so I can test it some more today. I will report back with what I find

[MattyL]

Okay so I did some more testing and here’s what I found:

1. With the level sensor unplugged, the plug read out about 11.7-12 volts

2. I unplugged the plug for the in-tank pump; it read out 2.2v whether the level sensor was connected or not

3. High pressure pump read the same, 2.2v whether the level sensor was plugged in or not

I will note that the car did not start today, I’m imagining it has something to do with that fitting which I taped over for testing. No fuel sprayed out but it might not be getting correct pressure to run.

I also went ahead and checked voltage at both the fuel pump and main relays:

Main Relay: pins 87-87 read about .5-.6v, pins 86-30 read the same

Fuel Pump relay: could not get a reading, pins 87-30 read well above 100v and kept increasing so I could not accurately get a reading

Both of those relays are brand new. I’m almost back to possibly trying the OBC bypass to see if that changes anything but I am open to other suggestions

[MattyL]

I also ohm’d the relay sockets as well

Main Relay: 8 ohms with the ignition off, read as “open line” when ignition was switched on

Fuel pump relay read as an open line no matter what

[MattyL]

I keep jumping around here. I discovered that my reference and speed sensor plugs are completely disintegrated. I pulled them out and they crumbled apart, I was able to clean up the prongs at least and plug them back in. After doing so it seems the fuel pump started working properly and was spraying fuel out of that broken part in the line.

My question is now this since I am planning on replacing both of those: Can a failing reference and/or speed sensor result in no fuel but still giving me spark? 

[1st 5er]

I think, "yes".

A rule I learned here years ago, when cranking if the tach does not move your issue is pre-ecu, if it moves your issue is post-ecu.

Reference sensors are pre-ecu.

[MattyL]

I was able to break away all of the plastic on the connectors for both sensors, they were literally held together with electrical tape. I also cleaned up the prongs and plugged them back in and the pump came back to life. That’s good info for future reference, although the tach does move when cranking it is never consistent; it can hover around 100rpm or jump all the way up to 2k. Going to replace both of those sensors and see if I get a change in the starting behavior