1992 BMW 730i (E32-M30) hard starting and rough running
Discussion
Hello folks, I'm looking for some thoughts on my 1992 BMW 730i with the 3.0 M30 engine which seems to have developed an issue while I've been away on holiday for a month. It's now often (but not always) difficult to start, and it also wants to stall on quick application of the throttle, although gentle application allows the engine to rev smoothly.
Before I went away on hols, the 730i always started with one or two seconds of cranking, and it was so reliable that I've actually been using it as my daily despite me having other younger and more fuel efficient cars - but none of them are nearly as comfortable as this is.
One thing I've noticed is that the fuel pump in the tank doesn't seem to ever prime when you turn on the ignition before cranking the engine. All other cars of that era that I've been familiar with always primed the fuel system before cranking. I can hear that the fuel pump IS working when the engine is running, but I can't hear it before or during cranking. Possibly it is running during cranking, but if it is it's far too quiet to hear it above the noise of the starter.
Another thing I've noticed is that the fuel hose that runs between the fuel rail and the fuel pressure regulator was loose. Despite the screw clamp, I could pull the hose off the nipple easily without much pressure. Could it be that air is getting in and letting fuel drain away back to the tank? The service manual I have tells me that the fuel system is designed to retain pressure even when the engine is off. When I pulled the fuel pressure regulator hose off, a bit of fuel spilled out but there was certainly no pressure in there.
I've found a page on bimmerforums discussing a similar issue (https://www.bimmerforums.com/forum/showthread.php?2390117-Starting-Issues-M30), and one of the things mentioned was crankshaft position sensor. I can't find such a thing for the M30 engine so over the weekend I plan to check the crankshaft position sensor. I don't have a scope, but perhaps I can test it with my multimeter. I've also ordered a new fuel filter. Air filter was checked and is spotless.
Any other suggestions? Here's a video of the issue from yesterday evening:
Edited to add: I don't think my switching off the headlights before it starts has much to do with it - as you can see it cranks strongly.
Before I went away on hols, the 730i always started with one or two seconds of cranking, and it was so reliable that I've actually been using it as my daily despite me having other younger and more fuel efficient cars - but none of them are nearly as comfortable as this is.
One thing I've noticed is that the fuel pump in the tank doesn't seem to ever prime when you turn on the ignition before cranking the engine. All other cars of that era that I've been familiar with always primed the fuel system before cranking. I can hear that the fuel pump IS working when the engine is running, but I can't hear it before or during cranking. Possibly it is running during cranking, but if it is it's far too quiet to hear it above the noise of the starter.
Another thing I've noticed is that the fuel hose that runs between the fuel rail and the fuel pressure regulator was loose. Despite the screw clamp, I could pull the hose off the nipple easily without much pressure. Could it be that air is getting in and letting fuel drain away back to the tank? The service manual I have tells me that the fuel system is designed to retain pressure even when the engine is off. When I pulled the fuel pressure regulator hose off, a bit of fuel spilled out but there was certainly no pressure in there.
I've found a page on bimmerforums discussing a similar issue (https://www.bimmerforums.com/forum/showthread.php?2390117-Starting-Issues-M30), and one of the things mentioned was crankshaft position sensor. I can't find such a thing for the M30 engine so over the weekend I plan to check the crankshaft position sensor. I don't have a scope, but perhaps I can test it with my multimeter. I've also ordered a new fuel filter. Air filter was checked and is spotless.
Any other suggestions? Here's a video of the issue from yesterday evening:
Edited to add: I don't think my switching off the headlights before it starts has much to do with it - as you can see it cranks strongly.
Edited by LunarOne on Friday 25th August 18:19
I can't think of any efi car that doesn't routinely have the pump prime as you suggest on key on.
But if the pipe you state is actually from the rail to FPR, it should be a high pressure line. The only risk there of dodgy hose/clamps, are fuel leaks.
Air ingress is of no concern, and not a possibility. Fuel leaks are, so it seems odd fuel was not leaking, and you say also only a dribble when removed. Generally there is always some residual pressure in there even with the engine off.
I guess first easy steps....check it both engine off, key on, during starting etc
But if the pipe you state is actually from the rail to FPR, it should be a high pressure line. The only risk there of dodgy hose/clamps, are fuel leaks.
Air ingress is of no concern, and not a possibility. Fuel leaks are, so it seems odd fuel was not leaking, and you say also only a dribble when removed. Generally there is always some residual pressure in there even with the engine off.
I guess first easy steps....check it both engine off, key on, during starting etc
stevieturbo said:
I can't think of any efi car that doesn't routinely have the pump prime as you suggest on key on.
But if the pipe you state is actually from the rail to FPR, it should be a high pressure line. The only risk there of dodgy hose/clamps, are fuel leaks.
Air ingress is of no concern, and not a possibility. Fuel leaks are, so it seems odd fuel was not leaking, and you say also only a dribble when removed. Generally there is always some residual pressure in there even with the engine off.
I guess first easy steps....check it both engine off, key on, during starting etc
More googling suggests that many BMW cars of this era do not run the fuel pump before cranking. Seems strange but apparently normal. I ordered an injection fuel pressure testing kit, and today I plumbed a T-piece into the supply side of the fuel rail and got the following results:But if the pipe you state is actually from the rail to FPR, it should be a high pressure line. The only risk there of dodgy hose/clamps, are fuel leaks.
Air ingress is of no concern, and not a possibility. Fuel leaks are, so it seems odd fuel was not leaking, and you say also only a dribble when removed. Generally there is always some residual pressure in there even with the engine off.
I guess first easy steps....check it both engine off, key on, during starting etc
Engine off fuel pressure after a run - 2.0 bar
Engine idling fuel pressure - 2.5 bar
Engine rev fuel pressure - 3.0 bar
Cranking fuel pressure - 3.0 bar
Today the engine was very easy to start, but the issue of stalling on quick application of the throttle was still present. During testing I was unable to stop the engine from dying completely. After a stall, the engine took a few seconds of cranking to fire during which the fuel pressure was 3.0 bar, which seems normal. One thing I didn't try doing is disconnecting the vacuum hose from the fuel pressure regulator on the return end of the fuel rail.
After doing this testing, I took the car for a drive. It almost stalled several times when trying to pull away from a standstill, and the engine also sputtered when trying to accelerate. Symptoms of either low fuel pressure or bad crankshaft position sensor. So now I'm starting to suspect the CPS more and more. While driving the car, I would slow down to about 20 miles per hour and then accelerate through the sputtering (between 2.5 and 4.5k RPMs) after which it would accelerate smoothly to 6500RPMs. I did this multiple times, and each time the sputtering and hesitation became less pronounced. After about 25 minutes of this, the car has returned entirely to normal. It starts after no more than a second of cranking (although it has been doing that on every start attempt today), and now the hesitation and sputtering has completely disappeared. It's never been a quick car, but it now accelerates smoothly from a standstill to motorway speed with no hesitation at all. I'll try again tomorrow, and while I'm at it I'll replace the fuel filter which I picked up yesterday. I doubt that's the problem, but it's a £10 part and I doubt it's ever been done in 30 years.
Video:
Edited by LunarOne on Monday 28th August 00:05
Many years since i worked on one of those, but from memory, they have a million rubber hoses around the inlet manifold, these can perish and cause all sorts of problems, also the idle air valves usd to be troublesome often, a good clean usually sorted this.
Might be compleatly miss remembering, like i said has been along time, but worth a look, good check fof perished hoses was always spraying brake cleaner all round the manifold, especialy underneath it, when running, obviously take care,
Might be compleatly miss remembering, like i said has been along time, but worth a look, good check fof perished hoses was always spraying brake cleaner all round the manifold, especialy underneath it, when running, obviously take care,
richhead said:
the idle air valves usd to be troublesome often, a good clean usually sorted this
Idle air control valve has been checked and is moving completely freely. The way to check is to remove it and rotate it back and forth in your hand. It should clunk as the valve hits each end of out its range of travel, which it does. Also checked IACV connector resistances, which are correct.richhead said:
Many years since i worked on one of those, but from memory, they have a million rubber hoses around the inlet manifold, these can perish and cause all sorts of problems. Might be completely misremembering, like i said has been along time, but worth a look, good check for perished hoses was always spraying brake cleaner all round the manifold, especially underneath it, when running, obviously take care,
Yes, there are a myriad of hoses connecting to the intake both before and after the airflow meter. How does brake cleaner detect leaks? Are you saying that the engine RPMs will rise if there's a leak? Or something else? I've been thinking of buying or making a smoke machine (I do have an air compressor) - that might be a bit safer! I don't mind accumulating tools - sometimes I think me working on cars is just an excuse to obtain tools!GreenV8S said:
Poor running that cleared up after several hard acceleration runs might point to dirty plugs. That would also make it harder to start.
Not a bad shout - I haven't actually checked the plugs. But why would it go from running perfectly to running badly after a spell of a month standing from plug issues? Last night I was thinking about it, and remembered that the battery went completely flat while I was away. After I got back, I didn't even try to start the car for a week, so it was left for a whole month - enough time for the battery to get very low indeed. I'm wondering if there's an element of DME/ECU relearning being needed after a flat battery. I don't know how long it takes for the DME to forget after a battery disconnection. Is it straight away, or does its memory last a few hours? Maybe today I'll disconnect the battery for some period of time and then see if the symptoms come back after reconnecting...LunarOne said:
richhead said:
the idle air valves usd to be troublesome often, a good clean usually sorted this
Idle air control valve has been checked and is moving completely freely. The way to check is to remove it and rotate it back and forth in your hand. It should clunk as the valve hits each end of out its range of travel, which it does. Also checked IACV connector resistances, which are correct.richhead said:
Many years since i worked on one of those, but from memory, they have a million rubber hoses around the inlet manifold, these can perish and cause all sorts of problems. Might be completely misremembering, like i said has been along time, but worth a look, good check for perished hoses was always spraying brake cleaner all round the manifold, especially underneath it, when running, obviously take care,
Yes, there are a myriad of hoses connecting to the intake both before and after the airflow meter. How does brake cleaner detect leaks? Are you saying that the engine RPMs will rise if there's a leak? Or something else? I've been thinking of buying or making a smoke machine (I do have an air compressor) - that might be a bit safer! I don't mind accumulating tools - sometimes I think me working on cars is just an excuse to obtain tools!Smoke machines are ok, but you idealy want all the hoses under vacume to detect leaks, a smoke machine causes slight pressure, should still show any leaks, but poss not.if brake cleaner worries you, use something non flamable, like water spray, this will try and stall the engine, but avoid any electrics, this is why most old school mechanice tend to use something flammable. just be sensable where you spray it. and obviously no where near the air intake.
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