Fuel pump not priming - car slow to start - why?

[Kaldek]

If that's the case I would possibly suggest the idle stepper control (ISC)motor. Upon first crank it's slow to get into fast idle causing the stutter/low idle. But upon second crank it's already in position so no stumble. Maybe give it a clean.

Agreed. That was ScannerDanner's next suggestion (after ECT/IAT) too.

 

[NuffNuff]

damn cold weather, starts perfectly, no stumble.. nothing. hadn't started it for 3 days and it was sitting outside. only difference between being out side is my driveway is at a bit of an angle so all the fuel would go to the back

 

[Kaldek]

Hi folks, figured I should add in my experiences of the last few months. I took off overseas for work and this screwed all my diagnostics plans.

Anyway, in the cold weather we've had since I returned, the car starts perfectly every time. You would consider the following data points from that:

- A sensor is reading cold in hot weather (briefly) but reads normal in cold weather; or
- Some other cause not related to sensors still points to incorrect fuel metering (as above does) but the root cause is masked by cold weather

 

[eddyvr4]

very interesting.. now that you mention it, exactly the same here.. as the weathers gotten colder.. its starting almost first kick now, probably as good as it ever did... i never connected the dots that way.. could it be a worn seal inside the fuel pump (not the oring) that is better when the fuel is at a lower temp? so it doesnt loose prime so much when cold? just a thought.. i need to try a new fuel pump, i just know that if i DO buy a new one, then it WONT be the problem, murphys law...

 

[Kaldek]

could it be a worn seal inside the fuel pump (not the oring) that is better when the fuel is at a lower temp?.

I tested this extensively in previous posts. I hotwired the fuel pump AND monitored the rail pressure in real time, and I still did not eradicate the cold start stumble.

My belief to this point is still that the ECU is sending an incorrect fuel mixture to the car on first start. This points to the source being a sensor faultn or just odd settings in the stock ECU rom.

 

[NuffNuff]

Mine has been started once a week to once a fortnight in cold weather in Melbourne recently and not once has it stumbled

 

[Kaldek]

Interesting update at my end: it's super hot right here and the car is starting fine every time. The last maintenance item I performed was new lifters and an oil change.

 

[eddyvr4]

and i replaced my fuel pump - it made no difference (or to the pinging!)
it seems as though maybe a heatsoak condition exacerbates the issue. ie if its hot and i stop for a few minutes to fuel up, it starts pretty promptly. but if it sits for 15 mins then its quite slow to start and wont start till the second cranking.. maybe intake air temp sensor? i probably could log it..

ive had ISC problems in the past but the symptoms were different with erratic idling and poor idling. my idle is good hot or cold, once it starts..

 

[Kaldek]

It's odd that my issue is gone. I cannot figure how new lifters could affect it. Maybe a weird air leak now removed due to working in the area - intake, plenum, crank vent hoses etc.

 

[RicKii``]

ive noticed the stumble in my car on cold start is getting worse and worse. But on load, it'll accelerate slowly then boost will kick in. It was alot punchier. if i was crusing at 100 and then plant it, it would feel like its choking a bit, like something is holding it back. does that sound like the O ring or fuel pump? it has a walbro installed

 

[Kaldek]

ive noticed the stumble in my car on cold start is getting worse and worse. But on load, it'll accelerate slowly then boost will kick in. It was alot punchier. if i was crusing at 100 and then plant it, it would feel like its choking a bit, like something is holding it back. does that sound like the O ring or fuel pump? it has a walbro installed

It sounds opposite to what would happen if your fuel delivery was messed up. In my case when my fuel pump O-ring was suspicious, the car was leaning out on boost because that's where you need more fuel to match the volume of air being pumped by the engine.

Sounds more like a really bad air leak, OR an air metering problem. Have you done a boost leak test? I have a home made boost tester tool which works great if you have an air compressor you can regulate the psi output of.

If you have EvoScan and an OpenPort 1.3 cable, you can get a reading of the MAF signal at idle too. If it's way off even with air leaks removed as a possibility it shows your MAF signal is messed up.

Do you have a wideband fitted? That can tell you if the car is rich when it shouldn't be, due to incorrectly metered air. The air metering as I said can be off due to a correct measurement at the MAF (but a subsequent air leak in the intake and turbo piping), or due to an incorrect measurement caused by a faulty or dirty MAF.

Air leaks cause a rich mixture. Faulty MAF I believe causes lean running. I think they only fail by under-measuring the actual airflow.

I'd be interested in sitting in the passenger seat while you drive, monitoring the O2 fuel trims.

 

[Kaldek]

Lastly can you check your fuel pressure regulator? I like to eradicate those as a source of trouble by pulling off the vacuum hose at idle and checking to see if any fuel leaks out.

 

[RicKii``]

all good, i checked the fuel pump/filter and swapped them over and the problem was still there. did a spark test and one coilpack was the culprit. she drives as good as ever!

 

[Kaldek]

Coil packs! Far out was I way off the mark or what.

 

[RicKii``]

problem came back today so i guess it wasnt coilpacks haha. i'll change plugs and leads and see what happens. although now i have to crank the car up, then recrank and then she'll bog down and then burble back to life. sounds like the problem you guys are having now

 

[Kaldek]

problem came back today so i guess it wasnt coilpacks haha. i'll change plugs and leads and see what happens. although now i have to crank the car up, then recrank and then she'll bog down and then burble back to life. sounds like the problem you guys are having now

Just to be clear, the problem I was having only occurred on the first cold start of the day.

 

[Brenton]

Just to be clear, the problem I was having only occurred on the first cold start of the day.

I had this problem, hasn't occurred for months since I modified the dodgy aftermarket y-pipe and fitted a hard pipe to the throttle body, I'd say an air leak was the issue in my case..

 

[Kaldek]

Well whaddya know - I had the cold start stumble this morning.

Have literally not touched the engine bay in months.

 

[Pantera6]

This may or may not help... My car is completely stock; it started up the first time every time for over three years (across the weather spectrum in Melbourne). About four months ago, i replaced the in tank fuel filter (the one attached to the stock pump) and also the external fuel filter under the car - at the same time - with genuine Mitsi replacement parts. I cleaned and re-used the fuel pump to tank sealing gasket (the big O ring between the pump assembly and where it mounts to the tank) and reinstalled the stock fuel pump. Nothing else was touched or changed at the time.

I think after two or three "first start of the day" events since changing the fuel filters (car does not get driven every day), for the first time, I experienced the stumble issue described in this thread. Specifically, when the issue was occurring, the engine would catch and fire (the first time after cranking for about two seconds), but it would stumble at very low RPMs for about three seconds before the idle would shoot back up to the cold start spec ~1800 RPM. I also usually "prime" the pump and ignition for about two seconds (out of habit) for the first start, then depress clutch and crank - this has been consistent practice throughout my ownership.

Also worthy of note is that this issue was intermittent - i.e. I could go for three weeks without the issue and then, on occasion, it would come back. I've even been using the same grade fuel from the same petrol station all the time - so variables are limited. I can only think of the big O ring gasket (that I reused - and not to be confused with the O Ring for the Walbro aftermarket pump discussed in this thread) not sealing 100% and on certain days (depending on temp inside the car) this affecting the built in line pressure. Coming into summer, the car has been behaving normally again - I have not experienced this issue in the last two months (Nov/Dec) - seems to be back to normal...but I suspect it may return in the colder months! A new O Ring pump sealing gasket awaits!

 

[lh1034]

I've just started having this issue in the last few days..