Diesel stalling in hot weather

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wammers said:
Have you tried cleaning the plug connection to the timing solenoid, the one on the bracket near the lower side of the injection pump? If the modulation is drifting at idle and the number four injector is sending correct info about point of injection, it can only be the timing solenoid or the ECU causing it. The static timing cannot drift.
Click to expand...

No. Good call, I'll try and find that.

I took a trace of the EDC general readings yesterday. Coolant temperature and everything else looked OK. Mind you, it is running perfectly so not surprised. Was kind of hoping to spot a jump in the middle or erratic reading but all smooth.
 
Grrrrrr said:
So, following on from Wammers suggestion here (http://www.landyzone.co.uk/lz/f10/diesel-pump-timing-tool-set-dial-gauge-280977.html) to use the Nanocom to set timing ...

... I'm really mystified. The results of yesterday's tinkering are inconclusive as far as I'm concerned.

Is it possible to do without removing the manifold? Well, I checked my toolbox and none of my hammers could fit in. Plus, I couldn't "see" in my head what I was trying to achieve and I couldn't see an easy way of slackening off all the high pressure fuel pipes. It didn't take more than a minute to decide that for the sake of ease of access, 15 minutes to get the inlet manifold off was well worth it. Having done it I stand by this technique, especially if this is your first time at this.

I took the car for a good run and then parked up, got the Nanocom out and plugged it in for a baseline reading (air-conditioning off). The live readings on the screen showed timing modulation of about 83%. The live trace recorded agrees with this and can be found here (1): https://drive.google.com/file/d/0By7n3F7TXDU8MGJhWDhhOE9jRms/view?usp=sharing

I then whipped the manifold off, started the car, gave it a minute or two to get the coolant distributed and let the revs drop down to 750rpm to get a baseline without manifold (air-conditioning off). On-screen modulation of 80% agrees well with the live trace here (2): https://drive.google.com/file/d/0By7n3F7TXDU8VWZoWTlmaUdTdkE/view?usp=sharing

I then made a series of marks on the fuel injection pump (FIP) casing and timing cover, alternating between scribed using a bradawl and also a permanent marker so I had a crude gauge.

View attachment 70620

I completely loosened the nut on the bottom of the bracket on the rear of the FIP and slacked the front 2 nuts. What followed was an incredibly frustrating few hours of tapping the pump towards the engine to reduce modulation, tightening the front 2 buts, starting and warming, taking a trace and then tapping it back the other way to increase the modulation again. It seemed to either sit in the eighties or sit in the teens and refuse to stay anywhere in-between. A couple of example traces and photos of position are below. All done with air-conditioning off.

(3) https://drive.google.com/file/d/0By7n3F7TXDU8MjZNbDFxdVJrc2M/view?usp=sharing
View attachment 70621
(4) https://drive.google.com/file/d/0By7n3F7TXDU8bjdqRTZEem9fc00/view?usp=sharing

I then decided to be a little risky and leave the engine running while tapping the pump. Fortunately a neighbour had come out to show solidarity at this stage so I got him to sit in the car calling out readings with instructions to kill the ignition if anything looked at all out of control. What we observed had both of us foxed. If I left the pump at 11% modulation it seems to stay there. If I leave it around 83% it seems to stay there. If I leave it anywhere in-between, say 30% and lock it off, it stays at 30% for a short time and then creeps up to the eighties. If I put the air-conditioning on then the modulation rises, if I switch it off the modulation falls again.

(5) https://drive.google.com/file/d/0By7n3F7TXDU8ZEZlS0w0UzRFLVU/view?usp=sharing
View attachment 70622

After much mucking about I decided to call it a day. I got the modulatation on 40%, tightened everything up, put the manifold back on and then went for a drive. No difference as far as I could see. Once back I parked up and took a final trace (6): https://drive.google.com/file/d/0By7n3F7TXDU8WUk1TnZ6a1k1dXM/view?usp=sharing
View attachment 70623

Here it gets really weird. Everytime I put the air-con off the modulation drops into the 30s. Switch it on and it rises back up to 84% - pretty back where we started the day, even though the final position of the pump has clearly moved towards the engine. Similarly, if I rev the engine or drive for a bit and then stop and let it idle, the modulation one more drops back to the 30s / 40s but then slowly creeps back up until once more it sits in the early 80s.

I cannot get my head around this. Surely if it was mechanical then it'd just stay where it is? Which makes me suspect some sort of electrickery is somehow pushing it towards the stable values of either 80% (or 10% when the pump is turned more towards the engine). My feeling is that there's more than one thing affecting this and I don't have all the pieces of the puzzle yet.

Unfortunately I'm the sort of person who never reads manuals. I tend to work things out from first principle or ask someone and work it out from there. However, I'm getting the horrible feeling that I'm going to have to dig out as much as I can on the EDC module, the workings of the FIP and that mysterious hot-start fix that is fitted and try and map all the interdependencies because I just cannot get a model in my head that feels right at the moment. Unfortunately time is my enemy there, although admittedly there might be more of that if I hadn't been so busy marinating my brain in Chiltern Black ale last night!

Hope that's of interest to Brian / whoever.

J
Click to expand...

Were all those measurements taken on hot engine?
If yes, no wonder that it stalls with fuelling set between 11-18 mg/stroke.
With automatic transmission it wouldn't even start going on slight uphill.
 
N2O said:
Were all those measurements taken on hot engine?
If yes, no wonder that it stalls with fuelling set between 11-18 mg/stroke.
With automatic transmission it wouldn't even start going on slight uphill.
Click to expand...

At idle hot. What other setting would you like the fuelling at idle? His problem is a variation in modulation not fuelling.
 
6 mg/stroke maximum at idle hot and no load, around 8 mg/stroke when AC compressor on.
First set fuelling by tapping pump upper section(towards bulkhead will set it closer to spec), then check timing modulation - it's also dependant of fuel pressure inside injection pump.
 
N2O said:
6 mg/stroke maximum at idle hot and no load, around 8 mg/stroke when AC compressor on.
First set fuelling by tapping pump upper section(towards bulkhead will set it closer to spec), then check timing modulation - it's also dependant of fuel pressure inside injection pump.
Click to expand...

That maybe his problem HP pump failing or his timing solenoid leaking. Pump maybe internally tired. Signal from number four injector is all over the place which would indicate to me that internal pressure was up and down like a brides nighty.
 
N2O said:
There is nothing to loose trying to set it to proper parameters.
Internal pressure can be measured through threaded hole in pump housing on the block side.

Some helpful data:
BMW Workshop Manuals > 3 Series E36 325tds (M51) TOUR > 3 Technical Data > 13 Fuel System (M51) > 51 Inj.pump, Regulator, Mixt.regulator > 1 TD Distributor Injection Pump, Control Receptacle, Mixture Regulator M51
Click to expand...

That depends on if the pump has been played with, pump tops don't slide back and forth on their own. He needs to have 128 on the Nanocom at 750 RPM. If he has more or less than 128 at 750 RPM that would indicate that pump top position has been altered. None of that would change his modulation problem. He is not getting any quantity servo faults.
 
Mine didn't have any faults too when adjusted wrong, just dropping revs when D or R selected and impossible to take off. Sliding pump top does nothing to idle speed, only reaction to increased load changes.
 
N2O said:
Mine didn't have any faults too when adjusted wrong, just dropping revs when D or R selected and impossible to take off. Sliding pump top does nothing to idle speed, only reaction to increased load changes.
Click to expand...

Moving the pump top increases or decreases fuel by sliding the control collar backwards or forwards along the piston. Any change in idle speed that would produce is compensated for by quantity control servo and idle control adjusting fuel to maintain 750 RPM. Pump is set up very precisely on a test rig if the pump top is removed and not replaced exactly where it came from you will have problems. There is no evidence or at least none has been mentioned that the pump top has been removed. And as i said earlier even if it had, that would not give him his modulation problem. According to the OP the car pulls like a train.
 
Yeah, and needs hot start fix.
:D :D :D

Only improperly adjusted and sowly cranking ones need that sh##.
:D
 
N2O said:
Yeah, and needs hot start fix.
:D :D :D

Only improperly adjusted and sowly cranking ones need that sh##.
:D
Click to expand...

The only adjustment available is static timing. Yes slow cranking will effect hot starting but it is not the only cause. If the pump is tired the pump is tired no amount of buggering about will sort that.
 
Not only, trust me. Every mechanic who does BMW M51 and some VW diesels know that.
And setting pump on bench does not always guarantee that it will work correctly.
Hot start problem is programmed in starting maps for emissions reason.
Altering position of upper pump section can do wonders(even with hot starting - when improperly adjusted, control collar will not reach proper starting position - it's analogue situation to static timing), just don't be afraid to do that if you have access to live data diagnostics.
 
Interesting reading, chaps. Thanks for that. I don't have access to pressure testing equipment though. All readings were indeed taken on a hot engine at 750 rpm.

Strangely enough I took it to a BMW diesel specialist last autumn to have the fuel pump seals changed as preventative maintenance after seeing Dopey's and realising mine were older and had done more miles. He told me the pump was tired - think I mentioned this in post #1. On refitting the top of the pump we had a hell of a time and I mean a hell of a time. In the end we left it slightly loose and tapped the top of the pump until it ran properly. Even tightening the bolts was enough to knock it off 750rpm. Took many, many attempts on a late Friday night to get it right. Getting it wrong did raise and lower the revs, IIRC. You could hear the engine was wrong though. I was telling him it was wrong before he even looked at the diagnostics and my hearing is nowhere near perfect.

Hot-start fix: I was told this was a mix of things. I was told it was partly down to the pumps wearing and not liking the low-sulphur diesel but the main reason was low cranking speed from old corroded connections / tired starter motor / tired battery. The ECU map apparently was a bit optimistic at higher temperature with the minimum rpm expected of a running or starting engine. He did say he could replace the chip with a new map and sort things pretty easily. After a bit of reading I'm half-tempted to have a go myself if I can find a chip reader / writer at the right price.

Anyway, it was a nice evening this evening so I nipped out and whipped the top off the engine ECU box. The hot-start fix on mine cuts the coolant temperature wire (blue and grey, I think) in half diverting it through the hot-start box. 2 more wires appear to splice into the glow-plug relay (red and white) and what I assume to be earth (black). Disconnecting it made it crank a lot before starting and the glow-plug light no longer came on but bugger all difference otherwise.

What I did notice was that reading it in my hand (in the General section) I can see both the crank rpm and injector number 4 rpm. Both match. Occasionally they go a whisker out and a tiny delay before number 4 catches up.

I also noticed that if I hold the revs at any amount, say 2000 rpm then the modulation stays rock-solid on 50% give or take a few %. That seems to imply that tired pump might be issue and higher revs is enough to make the issues negligible. Makes me wonder if it is a reasonable assumption that if revs and load is not changing then maybe it is acceptable to take measurement at 1500 or 2000 rpm?

Would love to know all the things it takes into account when performing that timing modulation calculation because it clearly isn't just crank-speed and injector 4. Presumably if something affects it then it must be in the ECU and presumably the Nanocom can get a reading on it.

I also think that the problems above are not the direct cause of the stalling in very hot weather. I think they are contributing factors that set the stage for the failure. I guess the pump itself may even run slightly hotter and expansion crosses some sort of threshold and pump efficiency reduced to a level the ECU doesn't like and it cuts out. Or hot electronics somewhere start leaking and a value goes out of range. Presumably if I had enough readings from enough cars (preferably known good ones) then I'd have a range of reasonable values. Then I've just got to catch the bugger when it does it!
 
N2O said:
Not only, trust me. Every mechanic who does BMW M51 and some VW diesels know that.
And setting pump on bench does not always guarantee that it will work correctly.
Hot start problem is programmed in starting maps for emissions reason.
Altering position of upper pump section can do wonders(even with hot starting - when improperly adjusted, control collar will not reach proper starting position - it's analogue situation to static timing), just don't be afraid to do that if you have access to live data diagnostics.
Click to expand...

Ok carry on bodging. :);)
 
wammers said:
N2O said:
6 mg/stroke maximum at idle hot and no load, around 8 mg/stroke when AC compressor on.
First set fuelling by tapping pump upper section(towards bulkhead will set it closer to spec), then check timing modulation - it's also dependant of fuel pressure inside injection pump.
Click to expand...

That maybe his problem HP pump failing or his timing solenoid leaking. Pump maybe internally tired. Signal from number four injector is all over the place which would indicate to me that internal pressure was up and down like a brides nighty.
Click to expand...

Just re-read this and it finally sank in. I can be a little slow at times.

That's got to be it: internal pressure too low and so it is trying to adjust accordingly. After I rev it pressure builds up and as I come off the revs it reads correctly for a bit but as the pressure leaks back down and it goes into rough idle mode or somesuch. I've gone through the Fuelling, Switching and General traces I took with the Nanocom but cannot see fuel pressure anywhere, even though it is clearly a key input, unless it has a pseudonym of some sort. Bit disappointing that.

So, we can be pretty sure we know why the timing modulation is so high at idle and drifts. Bit more learning for me there and still not complete because I don't have all the standard maps the EMS uses.

Of course, it still doesn't explain the trigger for the stall on hot days. What pushes it over the edge?! Back to trying to determine all inputs and what the maps are and then watchful waiting.

Incidentally, on the Switches section I tried pushing the clutch pedal down and it made no difference whatsoever. I wonder if this is related to the Cruise Control fault I get everytime, even though it clearly records that it is NOT FITTED!
 
Last edited:
Just a thought based on no knowledge, if it is an internal fuel pressure problem, maybe in hot weather the viscosity of the fuel drops enough to cause the problem?
 
Grrrrrr said:
Just re-read this and it finally sank in. I can be a little slow at times.

That's got to be it: internal pressure too low and so it is trying to adjust accordingly. After I rev it pressure builds up and as I come off the revs it reads correctly for a bit but as the pressure leaks back down and it goes into rough idle mode or somesuch. I've gone through the Fuelling, Switching and General traces I took with the Nanocom but cannot see fuel pressure anywhere, even though it is clearly a key input, unless it has a pseudonym of some sort. Bit disappointing that.

So, we can be pretty sure we know why the timing modulation is so high at idle and drifts. Bit more learning for me there and still not complete because I don't have all the standard maps the EMS uses.

Of course, it still doesn't explain the trigger for the stall on hot days. What pushes it over the edge?! Back to trying to determine all inputs and what the maps are and then watchful waiting.

Incidentally, on the Switches section I tried pushing the clutch pedal down and it made no difference whatsoever. I wonder if this is related to the Cruise Control fault I get everytime, even though it clearly records that it is NOT FITTED!
Click to expand...

Is cruise control activated in BECM in diagnostic mode. Go into BECM diagnostic mode. Ignition off, Nanocom connected, you should see "Diagnostic mode" on message centre when selecting BECM on Nanocom. If cruise is active de activate it, if it is inactive, activate it then de activate it. See what you get.
 
Datatek said:
Just a thought based on no knowledge, if it is an internal fuel pressure problem, maybe in hot weather the viscosity of the fuel drops enough to cause the problem?
Click to expand...

Now that's a very good thought, as determined by someone else with even less knowledge.

Yes, it'd have to be hot for a while to warm the tank enough, I'd have thought. Thinking about it, there's a fuel heater on top of the filter and I've recorded higher fuel temperatures with no issues on other days. Worth keeping an eye on but I think the jury is still out!
 
Grrrrrr said:
Now that's a very good thought, as determined by someone else with even less knowledge.

Yes, it'd have to be hot for a while to warm the tank enough, I'd have thought. Thinking about it, there's a fuel heater on top of the filter and I've recorded higher fuel temperatures with no issues on other days. Worth keeping an eye on but I think the jury is still out!
Click to expand...
Maybe the FIP gets hotter in hot weather worsening the poor tolerances.
 
wammers said:
Is cruise control activated in BECM in diagnostic mode. Go into BECM diagnostic mode. Ignition off, Nanocom connected, you should see "Diagnostic mode" on message centre when selecting BECM on Nanocom. If cruise is active de activate it, if it is inactive, activate it then de activate it. See what you get.
Click to expand...

Nope. No cruise anywhere! Not in any module and all traces / setting recodings correctly state not fitted.

Occurs to me I won't have a clutch switch fitted as I don't have cruise control. There are 2 microprocessors in the diesel EMS (according to RAVE):

The following function blocks are provided in
microprocessor 1:
- Injection timing (start of injection) control
- Output of self-diagnosis results
The following function blocks are provided in
microprocessor 2:
- Injection quantity control with special start quantity
control and full load quantity limitation
- Engine speed control
- Running stability control and vibration damping
- Exhaust emission limitation and overheating
protection
- Cruise control

It then goes on to say:

Clutch switch

A switch fitted at the clutch pedal position is
connected to the ECM.
The switch detects when the clutch is depressed. This
input is used to deactivate the cruise control and
various driveability strategies.

If I have no switch and output is ALWAYS low, I wonder if the second module sometimes throws a hissy-fit?

I don't know if I have no switch, that's an assumption based on why other fitting if not required? Any idea where it would be if fitted? Top of the pedal, I presume?
 
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