Won't start!!

[chrismsullivan]

After refitting my CSV, AAV, a few AAV lines, the manifold pressure sensor hose and refilling the radiator with coolant, the car started right up. It didn't idle as hig as I might have liked, but a little playing with te idle adjust sorted that out.
Immediately I noticed that more air was sucking through the air intake. Which I then put down as the reason as to why the engine didn't smell as though it was running as rich.

Test drive time.
It warmed up a lot faster than it used to before the cooling system flush, but only ever went slightly over 80c on the temp gauge.
The oil pressure needle steadily dropped as the car warmed up, but always went straight up upon acceleration. It's interesting to note that before working on the CSV, AAV and coolant, the oil pressure was always right up there regardless of engine speed.

So I pull it into the driveway, shut it down and gave it a quick wash.

I go to start it again and it won't start. It turns over, but just won't start. I'm sure I've got fuel pressure as this has never happened before. I checked for leaks, nothing. I can hear the system priming on ignition.
The main point of difference I can notice is that the oil pressure is at zero when cranking the engine. It used to shoot straight up when swigging the key to the "on" position, now there's nothing.
A lengthy cranking period will see the pressure rise to about .05 bar and it will splutter a few times as if it's trying to start.

Any suggestions?

Cheers
Chris.

[chrismsullivan]

As an add on to this.. When it had cooled down (not completely cold), it started after cranking for about 5 seconds. Ran fine, drove for about 100 metres and stopped dead while driving. Thankfully just in my own street.

My own mechanical understanding tells me that this might be fuel related, yet when I'm cranking it, I can smell fuel. Starting when cold, but not hot also has me a little stumped.

[chrismsullivan]

A bit more info to add.

I started it again and it ran OK, to the point where I got it home and it stopped dead in the driveway.

Symptoms after here are that it will start after much cranking, but it runs very rough and struggles to get over 2000rpm. It also is spitting a heap of white smoke out of the rear. Then... without warning, it will clear right up, idling and revving as normal until it decides to cutoff again.
From there it's like a rinse and repeat....

So, we know it will start when it's cold... (determining that it's got compression and spark.)
Will run well to a point where it decides to cut out... For what reason I have no idea.
It will struggle to start after that... (maybe vapour lock? maybe flooded?)
When it does start it runs rough and spits out white smoke from the rear... (white smoke equals unburnt fuel right? It certainly smells fuel heavy)

I've just about run out of ideas at this point.

I'm almost certain that it's not related to the AAV or CSV refurb or the addition of new coolant into the system. (unless the CSV is on all the time, which would only really cause it to run rich, but not cut out or run rough??)

Although, as previously mentioned, the car did warm up a lot faster than it ever has for me previously and did get up to just over 80c, which it never has before.
What is related to warm start/warm, running on a M110 d-jet that I'm missing here?
Is it the dizzy or anything attached to it?

Any suggestions would be greatly appreciated!

Gotta love a project car.

Cheers,
Chris

[KenM]

No expert here Chris but reading this over a few times has a few questions pop up for me.

1. Your oil pressure certainly sounds low, too low I would think, is there some link between this and the rich running? Is the oil runny or diluted with fuel?

2. It does sound as if it's flooding almost, have you removed or disabled the cold start valve entirely to eliminate?

3. I'm wondering about air or vacuum leaks as well, especially if you had the MPS off, perhaps Oscar will have some more clues here.

No other brainwaves at the moment I'm afraid.

[chrismsullivan]

Thanks Ken.

The oil pressure is not too out of the ordinary when the car us actually running, aside from prior to today it never used to drop at all.
I did an oil change not too long ago and have hardly driven it since. Regardless I did check the oil and there's plenty of it and it looks in good shape.

In regard to disabling the CSV; yes, I've removed the power socket from it to eliminate it opening and pumping fuel through. Although if it's stuck open all the time, then removing the power probably won't make a difference. I guess I'd have to remove it entirely from the intake to be sure.

Vacuum leaks are certainly another option, but a vac leak wouldn't be affecting the running of the engine only occasionally would it?

[WGB]

Did you set the idle with a properly hot engine at the beginning.

If you didn't it is possible that as the motor warms up the AAV closes the idle air circuit completely and stops the motor - in effect the opposite of an air leak - and having had this occur it was also hard to start as the motor will be throttled shut at idle and any jiggling of the throttle to start it will probably flood it.

Try starting it hot with just a little pressure on the accelerator pedal so teh throttle plate is only cracked open.

It sounds more like you had an abnormal oil pressure situation before (?high idle) and a normal one now. My experience of 280 motors when they were new was 2 Bar of pressure at a hot idle and 3 bar immediately the motor revs started to climb - but down to 1 bar at a hot idle was still OK.

Bill

[wbrian63]

The main point of difference I can notice is that the oil pressure is at zero when cranking the engine. It used to shoot straight up when swigging the key to the "on" position, now there's nothing.
A lengthy cranking period will see the pressure rise to about .05 bar and it will splutter a few times as if it's trying to start.

I'm not sure about later models of the W116, but I do believe that your '76 model should have a mechanical oil pressure gauge. I'm assuming you mean .5 bar, not .05, as I don't know how you'd even see that small a movement on the gauge. .5 bar = 7psi, which is just fine for a cranking motor.

I could be wrong, seeing as your car is a 6-cylinder model, but everything I've read about MB's of this generation say that it is perfectly normal for the oil pressure gauge to drop considerably at idle when the motor is warm, but that once throttle is applied beyond 1500 rpm or thereabouts, the gauge should peg.

Regardless, oil pressure low, or oil pressure no, I don't think that would prevent the engine from firing, so long as fuel and spark are present at the right time.

With a "six", pulling the plugs is an easy process. When it behaves like this again (or if it is still having the fit), pull a plug. That will tell you for sure if it's a flooding condition - the plug will reek of gasoline, and may even be wet.

And - extra fuel equals black smoke, not white. White smoke = water in the combustion chamber = Bad things.

I suppose that after your short drive and stop for a wash, if the headgasket is leaking water into the combustion chamber, that could prevent an immediate start (assuming the volume of water isn't enough to hydro-lock the motor), but the effect shold be only temporary at best.

As others have suggested, check the oil to see if it's fuel-fouled. A stuck warm-up valve will dump huge amounts of petrol into the engine, way more than it can burn. Some of that fuel will wind up in the oil. That is a BAD thing - diluted oil will not protect the engine. If the oil is fuel-fouled, it will smell of gasoline - do an oil change immediately if this is the case, and check the warm-up valve for being stuck.

Please update the forum on what you find.

Good luck.

[Nutz]

Is temperature sensor 2 connected well? Is new MPS hose collapsing? Did you knock trigger point connection loose? Did someone in the past fiddle with CO adjustment screw on ECU to compensate? Did you disconnect MPS wiring harness and not press it back in tightly?

[koan]

White smoke is usually condensing water vapour on a cold morning, unburnt fuel is black smoke.

Another possible cause of white smoke is a leaking head gasket but that doesn't fit too well with what you describe but to be sure I'd remove the all the plugs when the engine is cold and inspect them for dampness then get someone to turn the engine over while you check if any water spits out  the plug holes.

Try a warm start with throttle opened slightly as WGB suggests and use Nutz's D-Jet expertise to help diagnose.

The fact that "without warning, it will clear right up" sounds like an electrical intermittent.

koan

[chrismsullivan]

Thanks to everyone for your prompt and informative replies. 

In responding to everyone all at once; I think this will be one of the biggest posts I've ever completed.

Did you set the idle with a properly hot engine at the beginning.

If you didn't it is possible that as the motor warms up the AAV closes the idle air circuit completely and stops the motor - in effect the opposite of an air leak - and having had this occur it was also hard to start as the motor will be throttled shut at idle and any jiggling of the throttle to start it will probably flood it.

Try starting it hot with just a little pressure on the accelerator pedal so teh throttle plate is only cracked open.

It sounds more like you had an abnormal oil pressure situation before (?high idle) and a normal one now. My experience of 280 motors when they were new was 2 Bar of pressure at a hot idle and 3 bar immediately the motor revs started to climb - but down to 1 bar at a hot idle was still OK.

Bill

Bill, you raise an excellent opening question. No I did not set the idle with a warmed up engine. I adjusted it before the run.
Hopefully I can start it from cold and it will run for long enough to warm up enough to correctly set the idle speed with the idle adjust screw.
I think I will also need to increase the idle stop screw on the air intake throttle flap as I took that all the way down while I had things pulled apart and didn't reset it.

I've got a copy of the WSM idle adjustmet instructions on hand and will have a crack at that as an easy first step.

Thanks for the confirmation regarding the oil pressure situation. I'm glad that one thing seems to be operating normally now.

I'm not sure about later models of the W116, but I do believe that your '76 model should have a mechanical oil pressure gauge. I'm assuming you mean .5 bar, not .05, as I don't know how you'd even see that small a movement on the gauge. .5 bar = 7psi, which is just fine for a cranking motor.

I could be wrong, seeing as your car is a 6-cylinder model, but everything I've read about MB's of this generation say that it is perfectly normal for the oil pressure gauge to drop considerably at idle when the motor is warm, but that once throttle is applied beyond 1500 rpm or thereabouts, the gauge should peg.

Regardless, oil pressure low, or oil pressure no, I don't think that would prevent the engine from firing, so long as fuel and spark are present at the right time.

With a "six", pulling the plugs is an easy process. When it behaves like this again (or if it is still having the fit), pull a plug. That will tell you for sure if it's a flooding condition - the plug will reek of gasoline, and may even be wet.

And - extra fuel equals black smoke, not white. White smoke = water in the combustion chamber = Bad things.

I suppose that after your short drive and stop for a wash, if the headgasket is leaking water into the combustion chamber, that could prevent an immediate start (assuming the volume of water isn't enough to hydro-lock the motor), but the effect shold be only temporary at best.

As others have suggested, check the oil to see if it's fuel-fouled. A stuck warm-up valve will dump huge amounts of petrol into the engine, way more than it can burn. Some of that fuel will wind up in the oil. That is a BAD thing - diluted oil will not protect the engine. If the oil is fuel-fouled, it will smell of gasoline - do an oil change immediately if this is the case, and check the warm-up valve for being stuck.

Please update the forum on what you find.

Good luck.

You're right Brian, the oil pressure guage is mechanical and I did mean .5 bar, not .05. Again, thanks for confirming that oil pressure is as it should be.
I too was of the opinion that the oil pressure shouldn't cuase the car not to fire.

I'm pretty certain that the engine isn't water fouled, given that it will run rough and then clear up and run smoothly until completely cutting out.
The smoke coming out of the back isn't actually a pure white like you'd see if there's water present (seen that before), it's more of a blueish colour I guess and smells like raw fuel.

In regard to the warm up valve suggestion - The D-Jet models don't have a waqrm up regulator, so we can strike that one off the list.

I'll certainly keep everyone informed as to the oucome.

Is temperature sensor 2 connected well? Is new MPS hose collapsing? Did you knock trigger point connection loose? Did someone in the past fiddle with CO adjustment screw on ECU to compensate? Did you disconnect MPS wiring harness and not press it back in tightly?

Cheers Nutz...|

Please point me in the direction of temp sender 2. Is that the one that attached to the air feed pre intake manifold, in the same area as the AAV intake?

Trigger points = breaker points, on the distributor. Right? If so, I didn't actually do anything to that area throughout the course of the work just done, although I will check the connection of everything and the control line.

The new MPS hose doesn't appear to be collapsing, it's actually a fuel hose, so it's quite thick and has the braided inner.
The oil looks good (not cloudy or smelling heavily of fuel).

Aa to whether someone in the past has fiddled with the CO adjustment screw on the ECU... I have no idea. I never have. Considering the car was running previously, you'd think that this wasn't the issue at the moment... But who knows!

I had disconnected the wiring harnes from the MPS, and made sure that it was connected properly in place again.

White smoke is usually condensing water vapour on a cold morning, unburnt fuel is black smoke.

Another possible cause of white smoke is a leaking head gasket but that doesn't fit too well with what you describe but to be sure I'd remove the all the plugs when the engine is cold and inspect them for dampness then get someone to turn the engine over while you check if any water spits out  the plug holes.

Try a warm start with throttle opened slightly as WGB suggests and use Nutz's D-Jet expertise to help diagnose.

The fact that "without warning, it will clear right up" sounds like an electrical intermittent.

koan

koan, thanks mate.

I'm pretty certain that the smoke coming out of the rear isn't related to water ingress into the engine.
I will inspect all of the plugs (I expect to see them damp with fuel as there is a strong fuel smell while trying to start the car).

Hopefully, now that I've stepped away from it and had time to think of a few different options, I can narrow it down to a bad tune from the idle speed screw, the idle stop screw, electrical from the dizzy or control line.


Thanks again to everyone for your replies.

It's bound to be something stupid that I've done. A simple removal and reinstall of the CSV and AAV can't have cased this. It's got to be something that I've done to the idles screws or I've knocked something in the electrics.

Like I mentioned earlier, hopefully I can get it started from cold and it will run long enough to warm up to a point that I can adjust the idle properly, which will hopefully solve the problem. Fingers crossed for it being that simple.

Cheers,
Chris

[chrismsullivan]

Ok, a brief update.

Upon arriving home from the office, I went about checking all intake lines and increase the idle stop a little.

It fired up straight away, with a few splutters, which I put down to running like crap the last time I switched it off.
The idle smoothed out and it was running well for a few minutes at around 1500rpm. All of a sudden the idle started hunting, 0rpm back up to warm up idle speed.

After around 30 second of this, it stalled and wouldn't restart without the rough idle and fuel smelling smoke.

I hope that provides some further clues!

Cheers
Chris

[Big_Richard]

thats an electrical issue.

idle hunt is almost always caused by a stuffed sensor, wiring or other electrical issue - or even said sensors being misplaced or nonfunctional not in their own right. ie, a vacuum leak in the line going to a manifold pressure sensor.

[Nutz]

Are you absolutely sure the ignition system is up to par? Points (low tension cable snug, gap correct), wires, plugs, cap, rotor, coil (does it have a bulge on the center 'tit' #4) ,dwell set correctly?

[chrismsullivan]

thats an electrical issue.

idle hunt is almost always caused by a stuffed sensor, wiring or other electrical issue - or even said sensors being misplaced or nonfunctional not in their own right. ie, a vacuum leak in the line going to a manifold pressure sensor.

Thanks mate. I'm suspecting there's a problem with the sensor that plugs into the side of the air feed, pre throttle flap.
It was reading nothing when tested for ohms. I'll try unplugging it and going from there.

Are you absolutely sure the ignition system is up to par? Points (low tension cable snug, gap correct), wires, plugs, cap, rotor, coil (does it have a bulge on the center 'tit' #4) ,dwell set correctly?

Thanks again. I can't be 100% certain on the above. All I know is that it was running well (side from low idle at start and running rich) on Saturday and then wasn't after the work performed. It's got a new dizzy cap, new leads and plugs, new rotor. I'm unsure how tomcheck for the other things you've mentioned (low tension cable, gap, coil bulging on the centre tit #4, dwell.

Chasing electrical gremlins is something I'm not as confident with as I am with good old wrenching!

[chrismsullivan]

With a little further fiddling today, I'm no further along, apart from being pretty certain that it's not a vacuum problem.
The hunting idle seems to have subsided and replaced with missing a few times and then just cutting out.

I pulled the plugs and they are damp, black and heavily laden with soot. I also checked the oil, and it appears to be smelling of fuel more than it used to and also appears a little thinner.

Would an injector leak(s) be causing the OK on cold start, cutting out when warming up, not warm restart issue?

I guess the main thing I'm struggling to comprehend is that all this happened without warning, so I'm trying to think of how any of the work I've done might have caused the issue.

Maybe a strip down of the intake manifold, fuel rail, injectors, and distributor are in order instead of trying to fix insitu?