rawky

Hi Everyone,

All is well in the world of Pork, but recently the car has been hard to start when cold. Over the last few days, I have had the car taking 10 or more seconds of cranking to start.
When this happenes, the car finally starts but then idles at 150rpm and wont rev for a while before it frees up for some reason and it is fine. This has only happened when I have gone to work in the morning when it is much colder, but that could be a red herring...
Once the car is running it is completely fine, but starting it recently has been difficult.

What to check? MAF? LH? Any ideas?

Cheers
Rawky

AO

What year is the car?

rawky

Sorry, newboy error! It's a 1991 S4.

BTW I just remembered that MPG has been a bit lower recently, I thought it was the recent cold weather, but could this be a symptom of the MAF making the car run rich? Also, when I last looked at the spark plugs, there was a bit oil in there. I presume that is the Valve Cover Seal going? Could this contribute to bad running?

AO

Here are the usual culprits (in no particular order):

1. Temp II sensor - Take an ohm reading from each post to ground. When cold (say 10°C) resistance should be around 4k ohms.
2. Ground points - All your ground points should be clean and free of any corrosion
3. Fuel pump/fuel pump voltage/fuel pressure - This is what came to my mind. I would check the fuel pump output when the car has sat overnight. I forget the normal output of the pump, but I think it's 1 liter every 30 seconds? You can look this up in the manuals.
4. Ignition system (Cap, rotor, plugs, wires, coil) - You should check to make sure all these components are in good working condition.

THe LH could also be casuing this, but there's no good way to test except to swap it out.

I don't think the maf comes into play on cranking/starting.

My thought is it's either not getting enough fuel, or not enough spark. I suspect fuel, becasue it does finally start and gets better as it warms up. I think you may have a weak/sticking fuel pump.

John Speake

Andrew is corect, that when cranking the LH ECU has a default injector pulse width. Not affected by MAF.

Are you sure the car is running on all 8 when it first starts ?

rawky

Ok everyone, thanks for the quick replies!

Andrew, I have a good multimeter, so could either you or someone else give me a quick prompt on how to do these tests? I suppose the posts you speak of are the posts which connect into the computers? Do I check the resistance on every circuit? What is the method to actually do it?

I'll check my grounds yes....

How do I check the fuel pump? Tools needed? Is there a write up?

Once I have done all this I'll try the ignition components, and if that fails I can assume it's the LH?

John, yes the car does run on all 8. The idle starts out very low (150rpm), with me having to use the throttle to keep it going, but it straightens out and eventually it runs fine....

AO

To check the Temp II sensor, unplug the harness from the sensor. In the sensor, there are 2 pins. Use your multimeter to measure ohms between a pin and ground (chassis).

If you don't know which is the Temp II sensor, look at this picture. It's #2. (Thanks to Tony)

rawky

Ok Andrew thanks alot, so I test resistance on each individual pin of which there are 2. Each time measuring resistance between the pin and a good ground.... What should the ohm readings should I get from each pin?

Cheers
rawky

Btw, I'm guessing this is an easy part to replace? What is its purpose out of interest? How will its malfunctioning affect the car this way?

AO

Yes, you've got it. You should see about 4k ohms on a cold engine at about 10°C from each if the pins.

It's function is to tell the car what the temperature of the coolant is and thus how much to enrichen the mixture or adjust ignition timing. It's easy to replace.

rawky

Ok, I'll report back on this thread when I've inspected it.

How do you measure fuel flow for future reference?

Cheers
Rawky

AO

Remember you asked...

Well you don't have a fuel pressure gauge, so the best we can do is to see if the flow is correct.

In the picture above, you'll see #23 is a fuel pressure gauge. Normally, there is a cover over that fuel rail. You need to remove this cover. On the end of the fuel rail is a nut. Remove this nut. Don't smoke, fuel will come out - you could go BOOM!

Hook up a hose to the fuel rail. Have the other end of the hose in a bucket or some other catch.

Go to your fuse/central electric panel and locate the fuel pump relay. Not sure where it's located on a RHD car. Remove the relay. Then, with a toggle switch and some wire (15amp rating should do it) jumper pins 30 and 87 (use the relay for reference). Turn the switch on for 30 seconds.

You should see at least 1.35 liters of fuel in that 30 seconds.

If less than that, you're net getting enough fuel.

rawky

Sounds dead easy (famous last words)

Cheers, I'll come back with results hopefully over the weekend.
Rawky

John Speake

You should measure that fuel flow at the return to the top of the fuel tank. Then you know you get that return flow at rated fuel pressure..... as per the WSM.

Open boot (trunk) lift carpet on RHS and then remove the rubber bung, undo return fuel pipe, extend into suitable container. Carry out test as Andrew described, at least 1.35 liters of fuel in 30 seconds.

rawky

UPDATE

We may have found our problem, I tested each post as described. On the 20k range, I got resistances of 10.2kΩ and 10.01kΩ. So should I be ordering a new Temp II?

Cheers
Rawky

BTW - My rear window defroster stopped working recently, and I have just found the fuse melted to a crisp! I'm now anxious about putting a new one in incase it starts a fire! What is causing this temperature?! A short circuit somewhere?

Mrmerlin

if you worked on the hatch then there is a good chance that the thick defrost wires may have gotten pinched along the sides of the trim clips