Car will start and idle, dies when driven

The little car has developed a new problem. It coughed and died. It would start, then die again. It seemed like a fuel filter issue, so we replaced that. However, car starts idles well, then died 1/2 mile from home.
Where do we begin?

Check the fuel pressure... should be around 2.5-3.0bar depending. 37psi-44psi area.

I think I need a bit more help here. "Install pressure tester 13-3 060 with connecting hose and adapter 13-3 064...Plug fuel return line with Special Tool 13-3 010....Bridge terminals with Special Tool 61 3 050" Are there tools other than these Special Tools that will get the job done?

$20 harbor freight fuel injection test kit and a pair of vice grips works too. Harbor freight kit comes with a fuel pressure gauge and fittings/tees. Pinching the return line with vice grips will show You dead head pressure.

L Jetronic and Motronic tend to be very sensitive to fuel pressure so even a few lbs off would make me suspicious. Make sure to inspect the in-tank filter pump and sock assembly before replacing the main pump. If the in-tank pump's clogged or dying it can make life harder for the main pump.

Link here:
http://www.harborfreight.com/fuel-in...ter-92699.html

Originally Posted by Alfa Seltzer

$20 harbor freight fuel injection test kit and a pair of vice grips works too. Harbor freight kit comes with a fuel pressure gauge and fittings/tees. Pinching the return line with vice grips will show You dead head pressure.

L Jetronic and Motronic tend to be very sensitive to fuel pressure so even a few lbs off would make me suspicious. Make sure to inspect the in-tank filter pump and sock assembly before replacing the main pump. If the in-tank pump's clogged or dying it can make life harder for the main pump.

Link here:
http://www.harborfreight.com/fuel-in...ter-92699.html

What he said!

I have a similar problem with my 87 e30. It starts and runs, fine for about 5 minutes of driving, then starts to get rough and act like it's out of gas. Because of this, I decided to start with the fuel filter, since it's cheap and easily replaced. However, that hasn't solved the problem, and since the next cheapest part is the main pump, as soon as that arrives I am trying it. My question is this - on my old 86 eta model, I could hear the pump always, and I have never noticed it on this model, so I don't know really if it's running at all, but I suspect the car wouldn't start or run if the pump was completely dead. Is it possible for the transfer pump to supply enough pressure to run the car, or can the main pump fail in a decreasing pressure mode, where it goes gradually? I suppose I'll know as soon as the new pump arrives and it's installed, but...if this fails to fix the problem, what next? Transfer pump, or search elsewhere? Why is the transfer pump twice the price of the main one? Ugh. I don't have the test kit, but suppose it's a worthwhile investment...

With a part as pricey as the fuel pump I would suggest confirming Your issue lies there before replacing it.

I'd start out with checking Your Coolant Temp Sensor and if the car refuses to start when this issue happens try unplugging the MAF. Check for voltage at the fuel pump when cranking and listen for any odd noises from the pump itself. If You know anyone handy with an Oscilloscope you may be able to save yourself some trouble by checking the pump with that.

Originally Posted by scism

I have a similar problem with my 87 e30. It starts and runs, fine for about 5 minutes of driving, then starts to get rough and act like it's out of gas. Because of this, I decided to start with the fuel filter, since it's cheap and easily replaced. However, that hasn't solved the problem, and since the next cheapest part is the main pump, as soon as that arrives I am trying it. My question is this - on my old 86 eta model, I could hear the pump always, and I have never noticed it on this model, so I don't know really if it's running at all, but I suspect the car wouldn't start or run if the pump was completely dead. Is it possible for the transfer pump to supply enough pressure to run the car, or can the main pump fail in a decreasing pressure mode, where it goes gradually? I suppose I'll know as soon as the new pump arrives and it's installed, but...if this fails to fix the problem, what next? Transfer pump, or search elsewhere? Why is the transfer pump twice the price of the main one? Ugh. I don't have the test kit, but suppose it's a worthwhile investment...

I would say convert you car to a single pump from the later model E30's you then have to pur in substitute to replace the old outside pump. I used a brass 3/8 to 1/2 from lowes and the later a check valve. Its very simple and no noise out side the car and only one pump to deal with.

It could really be a whole bunch of different things. I suggest unhooking the main pump and on the other side remove the line that goes to the fuel filter since yours is up front. Put a shot or too of air down the metal fuel lines. You could have a possible clog in the line. Also get a 15oz bottle run the hose into the bottle. Should be about 15oz in about 15 seconds or less. If thats is full with in that time the. Your fuel pumps are fine.

Is there a thread or post or something that provides a good list of all the diagnostic tools one should have for these olde e30's? And how to use them. Even Bentley presupposes some knowledge of the various tools...

Greg Gordon has a good guide for Motronic Basic which applies to earlier E30s:

http://www.hiperformancestore.com/Motronic.htm

This is very helpful, but does require a lot of cross referencing, as the car I'm looking at is a 325i with a Motronic 1.1, and the pics are very different. So far, still waiting on the pressure tester, and working through the checklist of voltages.

I am not so au fait with these vehicles, but something just went- click !
If I am assuming that a feed pump feeds fuel to a fuel pot (the small tank that sits in your boot) & from there the high pressure pump takes over
Then it could be that your feed pump is not doing its job properly anymore & that your car only travels so far, till your Fuel pot runs dry
I am not sure how many gpm the feed pump is supposed to deliver, find that out & test it
Oh yes, & check the fuel strainers for obstruction. I have already found a Handkerchief blocking one intermittently

without reading the storybook above (to steal steves words lol) my money is on the AFM

I had a problem similar to these mentioned.....car would start and idle fine but would suddenly die while driving.

Turned out to be the fuel cap was not venting air into the tank so you would get a big vacuum "whoosh" when you removed the fuel cap.
Worth a try to see if the problem occurs with the fuel cap removed temporarily!

I am not sure if these E30s have a seperate vent valve or use the fuel cap.

Continuation: The little beast now does not start. Cranks strongly, but does not catch. Working through the information listed at http://www.hiperformancestore.com/Motronic.htm has been a bit challenging, as the pics look nothing like the 325i with Motronic 1.1, so finding things gets tricky. Some good diagrams at realoem, but not quite the one I sought. A post on another thread had someone saying that this model has only one fuel pump (1991) rather than the two, but the real oem diagram found through their helpful chat person does have two. It's production date was 10/90, in case that helps. The pressure tester arrived today, but "There are many fuel lines under the hood of an E28. However most of them are low pressure hoses. We need to take a fuel pressure measurement from a high pressure hose." And how do I tell a high pressure fuel line from a low pressure line? Again, the line shown in the picture isn't in that location in my car. There is correct voltage at the fuel pump relay, and the fuse is fine. All help is greatly appreciated.

Okay. On a M42 there is a fuel rail. Find it. The fuel runs into that and then into the injectors and whatever is not used via the the fuel pressure regulator is sent back thought the low presssure lines back to the tank. Look for the line that goes though your fuel filter which is under the car where the second fuel pump would be on early models 84-87. Which is on the drivers side under the car right before the rear wheels. Then fallow that line which turns into a metal line and then back into rubber and into you fuel rail. I'm not possitive but mostlikely comes int somewhere up front and the return is going out the back. The regulator is on the return side of the fuel rail. You should get a Bentley Manual.

As I understand it, this is M20, not M42. As a '91, does it NOT have the second fuel pump? In which case, if "They have a low pressure "transfer" pump located in the fuel tank, and a relatively high pressure "main" fuel pump located under the car," does that mean the Main or only one is in the fuel tank? I've been trying to get the Bentley now for most of three weeks, but so far that effort hasn't worked out. The regulator is at the front of the motor, so I shall look more at the back for the incoming fuel line.

My car is doing something similar to this and me and my father troubleshot it down to a vacuum line possibly..sorry if it doesn't solve your problem or if it isn't right but it's solved problems similar to this one. I'm still looking for ways to get my car running right again after replacing the vacuum lines, I hope it works again.

We continue slogging through the possibilities. I welcome the input.

Your 91 has one pump.. I got a extra known working pump laying around if you wanna throw me 15 plus shipping . I would also check you're maf sensor. I'm guessing your pump took a crap pm me if you want it.

The offer is much appreciated, but we already had one on the way from AutohausAZ. Got it installed, and the little car is up and running again. The project did take a few detours, but it seems as if repairs usually do. I appreciate all of the suggestions and assistance.

Happy days

I had the same problem. After a ton of different parts, injectors, etc. I finally bite the bullet and replaced the following 4 all together. Which one did it, I don't know but my guess it was the fuel pressure regulator.

1) Fuel Pressure Regulator (at the end of the injection rail) $80
2) 1.5ft vacuum hose from the intake manifold to the regulator $3 (in case it was leaking and not providing vacuum to cause the fuel return)
3) Fuel pump relay
4) ECU relay

I did all 4 then SeaFoamed it. It hasn't stalled yet.

P.S. Before I did that, I cleaned and overhauled the MAF, removed, cleaned (WD-40) the idle control valve, replaced all 6 fuel injectors, replaced the ignition coil, distributor cap and rotor, new fuel tank cap, new oil filler cap (remember, the entire crank case on an E30 is pressurized so any intake or caps loose will cause a vacuum loss issue and stalls/rough running.

So I guess I got a real good tuneup while I was looking for the problem!