Another hot-starting issue.

[Philip Chidlow]

This time my motronic 8v GTi auto. There's a problem that manifests itself when the car's hot.

Background:
Starts fine every time from cold. Idles a bit high, but I can live with that. When stopped, in drive, the revs drop to around 900 rpm but it vibrates like a good 'un so (despite advice not to) I have to slip it into 'N' at which point it idles smoother (though not completely) at over 1000 rpm. There is some manual adjustment possible using the screw on the intake as GTi owners will know but this seems to have marginal effect.

When it reaches temperature, too, (around 88-90) it goes fine. Stop. Leave the car for a few minutes. Return: It's a bit of a bugger. It idles roughly, occasionally requiring two or three tries plus a blast of throttle to idle at all. Put it into D and it'll pull off sort of OK, into R is a slightly different as it can stall. Today the car was admittedly quite hot - just pre fan cut-in temp I guess. Parked up, came back and she refused to idle. Started OK, but died. Application of throttle didn't help much and got rather unhappy splutter and pop from the exhaust. When the temp had dropped after a few mins, it started OK (at around 90) - well as OK as I'm getting used to.

This problem has existed for a time now. It's had new NGK plugs, Magnecor leads - the battery's a new 440 amp jobbie and no warning 'k' light or otherwise are staying on...

Any thoughts on what I should do now?

[douglas851]

Sounds very similar to my warm starting problem.

I think the 8v has a different Motronic to the 16v?

[Philip Chidlow]

Yes it is, I believe (but with no workshop manual at hand, can't be sure)...

Another thing that's seems to be occurring now is it gets hot. It doesn't take much to get it over 90 and it quickly climbs if we're stuck in traffic for instance. I checked the coolant levels and condition: OK. No leaks. Radiator hot all over... I can suspect the thermostat maybe? And the fact she runs a bit hot might be contributing to the issue?

[douglas851]

If the fan cuts in I would not worry.

If it gets too high the big STOP light illuminates.

[sdelasal]

Sounds like a heat soak problem. Something is getting too hot as the engine is off after running - eventually it all cools down but initially temps go up. If you key off when its hot, can you re-start it instantly? Another test would be to open the bonnet after you switch off to stop temp build up - then try restarting at the time you think you normally get a problem. If that works, then its a matter of figuring out what's getting too hot. If not, well back to the drawing board! Steve

[Philip Chidlow]

Well, it does restart if I try straightaway. I think OK, it gets a bit hot, but that shouldn't cause it directly to cause starting/idling issues; Could it be a faulty electrical issue: possibly a temp sensor?

What would get inordinately hot under there? I wonder if there is an coolant, or even oil circulation problem?

I think I'll bung a new thermostat in for good measure.

[sdelasal]

If the fuel rail pressure is not being retained high enough, then fuel will boil in the rail - so you end up with air in therel. Start & idle is then poor until air is purged out and pressure returns. Thing to check would be fuel pressure - should be a test connection on the rail. I have a gauge you can borrow. Reasons why presure could be low are bad pump, bad pressure regulator or leaky injectors.

Ignition coils don't like the heat too!
Are your cooling fans working okay?

Steve

[Philip Chidlow]

Interesting. Maybe I'll take up your offer: it makes sense for me to drive over to you at your convenience, and we can have a play with the GTi. What do you reckon? What are you up to next week?!

[Vanny]

Check the rotor and cap, then the air mass meter, it's going to be an electrical problem somewhere i imagine.

[Philip Chidlow]

Going to have a stab at locating the problem tomorrow. Steve (sdelasal) has offered to help me.

[prm]

As your replacing the thermostat would also recommend replacing the rad thermo switch at the same time, for the lower TZD type, along with a 82?C stat.

Regards

[Philip Chidlow]

Over the coming weeks I want to get this sorted as it's becoming an irritation. It's a fine drive and it spoils the experience a bit. Although it will not solve the problem, I will change the thermostat, rad temp sensor (for the suggested TZD type) and do a coolant flush and refill. Just so I'm confident the car's cooling OK.

It's the later GTi with Motronic, not Jetronic. Can someone describe a course of action that would help me locate the issue (other than has been mentioned above). I am not sufficiently familiar with the workings of the fuel and injection system, so would welcome an Idiot's Guide to what the key elements are: for instance I need to be sure what I'm looking at re: distributor and rotor arm (unlike the Jetronic and Motronic 16v which I am more familiar with). The unit appears different. (Vanny suggests investigating this part of the system so that's what I will try to do).

But I am starting to think the problem maybe lies with the Air Flow (mass) Meter, (am I also right there's a throttle butterfly housing as per the earlier GTI too? Could this be at fault I wonder)... and Steve's suggestion about fuel pressure being retained in the rail: how would I check as there isn't a test connection on the rail that we could find...

Phil

[grecian]

have a read of the info in this link; it's about non starting but it may help you to eliminate some possible issues

http://forum.bmw5.co.uk/viewtopic.php?f=9&t=44121

[Jaba]

Phil - greetings and also apparently commiserations for your hot starting problem.
As previously mentioned you MUST check the fuel pressure in the rail. This should be held at or near to the 3bar regulated pressure for some time after you stop the engine.
Assuming you measure 3 bars and it falls away within - say 5 mins then if you can find the component that is leaking away the pressure then all will be returned to normal.
The components that can leak away the pressure are :
Any one of the injectors.
The fuel pump's non return valve in the outlet.
The pulse damper which contains a sort of accumulator as well.

Also, if the pressure checks turn out to be normal, which is of course quite possible then from my bitter experience you could have WATER in the petrol tank.
Is the filler neck rusting away at all and is the tank pressurised as witnessed by a gentle fart when you undo the petrol filler cap.

[Way2go]

This time my motronic 8v GTi auto.
Idles a bit high, but I can live with that. When stopped, in drive, the revs drop to around 900 rpm but it vibrates like a good 'un so (despite advice not to) I have to slip it into 'N' at which point it idles smoother (though not completely) at over 1000 rpm. There is some manual adjustment possible using the screw on the intake as GTi owners will know but this seems to have marginal effect.

The revs are too high at over 1000 on idle, you need to adjust to 900 when car is warm. At your revs there is a high drag through the torque converter which is also likely the reason you are going over temperature in traffic. In "Drive" mine is just below 800 with my foot on the brake.
If the adjusting screw is not working then the shaft of the second butterfly is likely "sticky" and the butterfly not returning fully under spring pressure, lubricate on the throttle body with 3in1 penetrating spray followed by 3in1 light lubricating oil.

The poor starting issues when hot I experienced before my injectors were cleaned, serviced and balanced but presumably as we've covered this issue before then you have already attended to this?

I need to be sure what I'm looking at re: distributor and rotor arm (unlike the Jetronic and Motronic 16v which I am more familiar with).

If as you say you have Motronic then you don't have a distributor and rotor arm as the motronic system utilises "wasted spark".