Cold start cutting out

Post Fri Feb 03, 2017 7:22 pm

Hi all,

The car's an 1989 325i with an M20B28 running a SpeedTouch chip on a Montronic 1.3. New CPS, new rotor arm/distributer, plugs, fuel pump, refurbished factory injectors. Original blue temperature sensor.

The car runs fine (overfuels a bit though - assume it's the map - I've got a Miller WAR chip waiting to go in once I've got time/an AFR gauge), except when it's cold. It idles a bit lumpy at the best of times (upgraded camshaft), and when it's cold it sounds like a V8 engined drag racer as it struggles.

Anyway, my problem is the first start when cold. If I crank the car and let it start, it cuts out immediately. If I repeat, it will do the same. If I repeat, but blip the throttle for a second, and then let off, it starts and idles without problems.

Any ideas anyone what causes the initial non-start? The fuel pump is on a kill switch, but even if I don't disable it between runs, I get the same problem. It's worse in the winter, but I don't recall if it did it in the summer.

It's getting an average of 23.5mpg during mixed, often spirited driving, so I don't think it's fuelling too badly, making me non-suspect the blue sensor (but I confess I've not tested it). Given it starts if you blip it, I don't think that's the cause anyway.

Cheers,
Joe

Post Fri Feb 03, 2017 7:58 pm

Injector(s) leaking? Mixture too rich to burn on initial cold start, until pushed out by cranking.
Monitor fuel pressure after stopping engine to check.

Post Fri Feb 03, 2017 8:07 pm

Thanks.

I don't think it's a case of too rich at start as it starts first time if you keep your foot on the throttle for a split second while cranking, or blip it within ~2 seconds of it starting. (It will start, run for a second or two, then die, unless you intervene by blipping it.) I'd expect it would not run at idle at all if it were too rich? (Far from an expert though, hence my asking

)

I'll check the fuel pressure. I'm guessing that it should be retained at roughly 3.5 bar for a good few hours? I know it isn't keeping pressure, at least overnight, as if you try and start it after it's been stood for a while, and forget to enable the fuel pump, there's not even a cough of life, just cranking.

I'll try and borrow a fuel pressure tester from someone, and grab a video next time I'm near the car (it's tucked up for winter, and not at my house). Assuming it is leaking pressure, is this exclusively the injectors, or also possibly the FPR? All fuel hard pipes and hoses are brand new.

If I need to buy a tester, would something like this be along the right lines? (Assuming correct adaptors etc.)
http://www.ebay.co.uk/itm/Car-Auto-Fuel ... SwU-pXus8Y

Post Fri Feb 03, 2017 8:36 pm

It says it works up to 10 psi?? can't be right?

3 bar is 43 psi - find one that works up to 100 psi maybe.

Paul

Post Fri Feb 03, 2017 8:44 pm

Good spot!

http://www.ebay.co.uk/itm/Fuel-Injectio ... 2217172110

Seems a better bet (so long as the adaptors all match up). But this is the right lines though, I'm barking up totally the wrong tree?

Post Fri Feb 03, 2017 8:48 pm

That one looks more up to the job!

Should be fine as long as the adapters fit.

Must get one for the tool kit!

Just saw it says not for Jetronic or Bosch or GM ???

Paul

Post Fri Feb 03, 2017 10:00 pm

True... I can't see why it would make a difference (I was thinking it's not a jettronic, I'd forgotten it is a Bosch tho.

I can't see why it would matter though, as you'd use rubber hose to connect to the t-piece inline with the existing fuel piping, and then that connects to the gauge using parts in the kit? (Unless I'm totally misunderstanding how it's used?!)

Post Sat Feb 04, 2017 11:16 am

I would be inclined to test the blue temp sensor before doing anything else:

http://www.e30zone.net/e30zonewiki/inde ... emp_Sensor

Post Sat Feb 04, 2017 6:10 pm

I shall do that as a matter of course, but I don't think it's likely to be at fault due to the short lived nature of the fault.

The gear linkage broke on my 330d earlier, so looks like the E30 will be roped into daily duties again so I can test it sooner rather than later anyway!

Post Sat Feb 04, 2017 6:55 pm

Also try cleaning out the ICV and checking/cleaning out the TPS.

Post Sat Feb 04, 2017 8:04 pm

Thanks. ICV was cleaned during the rebuild (IIRC), and the TPS is fine. I tested that as it wouldn't run at all at first, after I'd plugged the TPS and the ICV (I think?) into the wrong plugs. I didn't notice the wiring mistake at first, and was ruling out the mechanical bits first.

Post Tue Feb 28, 2017 7:16 pm

I hooked this up to a fuel pressure gauge today. It idles just under 3 bar, and if you sharply blip the throttle, it peaks just over 3. I think the fpr is OK. The pressure dropped off quickly (possibly due to a loose jubilee clip which later sprang a leak). With the engine warm and no pressure in the rail, it restarted as soon as the pressure was built up - about 2 second maximum.

What I did discover is that there's no signal to the ECU from the blue temperature sensor. At the sensor directly there is a reading of ~250ohm at just below running temperature. I need to test when it's cold, but it suggests the sensor is ok.

I'm hoping it's just a bad repair to the manifold plug and fixing that will bring it back to life. The smell of petrol in the garage was getting too strong to continue though!

What's the cars default stance when there's no signal from the blue temperature sensor? To run as per a hot engine? If so, hopefully this is the simple cause of my problem. I'll break out the multimeter and crimps tomorrow!

Post Thu Mar 02, 2017 7:24 pm

Fixed this earlier today by repairing the repair to the inlet manifold loom.

Now there's a signal from the temperature sensor it fires up first time and settles into a rock steady idle, something it didn't do before. Huzzah for simple fixes!

Post Thu Mar 02, 2017 7:30 pm

The problem you are describing should have had minimal effect on cold starting and idle at first, becoming increasingly as the car warmed up, and probably failing to run at full temperature. The spark plug tips should be a give away - they would be sooty and black.

Post Fri Mar 03, 2017 8:38 am

Hmm, strange. It's definitely an improvement when cold, so that's good. I didn't run it up to temperature as I was getting cold, and hungry, but it'll be interesting to see if there's an improvement.

It seemingly ran perfectly when hot though, no issues at all. I don't feel I can read too much into the spark plug colour at the moment as I'm not sure I trust the chip it in to be fuelling correctly. It stinks of fuel all of the time, regardless of temperature. I've got an AFR gauge waiting to go in so I can see what's actually happening with it, and can then get a map/injectors to suit (it's now 2.8, rather than 2.5).