Fuel supply problem.

[146ken]

It all started with the MOT about two months ago. My '88 740gl (2000cc 5speed) had been running ok till then. Returned with a slight misfire under load. This culminated in the car cutting out and failing to restart, right outside the MOT garage. They kept her over night and in the morning she started first time and no fault apparent. After several conversations with the garage they suggested the problem was there before MOT.
I got in a crypton tuning guy and he found they had wound the CO emissions down to 10% of MOT limit; his guess was they thought it had a cat. New plugs had burnt out and were replaced. also HT lead replaced.
Also noisy fuel pump, but pressure test showed fuel supply ok. Tuned up she was runnuing well again.
two weeks ago we loaded up and set off for a weekend away. 30 miles up the road she started misfiring and within a few miles was misfiring under any sort of load. Once cooled down she would start, drive for ten or twenty minutes then repeat the trick.
Garage identified the fuel pump as needing replacing.
Limped the car home in stages.
The main fuel pump( old one noisy) was replaced as was the intank pump(old one not working). Both now working well.
Now on test drive the problem reoccurs after 10 minutes. The intank pump is making the right sort of whirr, the main pump noisy and straining. on removing the petrol cap there was a whoosh noise, left cap off drove home no probs. Cap cleaned and now venting. The problem still occurs but no whoosh from cap.
Where do I go next?

[alsner]

Hi, is your car injection or carb? If injection which kind?

[146ken]

Yes it is injection. How do I tell which kind it is? What are the choices?

[alsner]

Originally Posted by 146ken

Yes it is injection. How do I tell which kind it is? What are the choices?

Check on the left hand side or front of the engine block and you'll see an engine code e.g B200e

Mechanical fuel injection is what I'm presuming being an 88 model (continuous injection system, CIS) should be relatively bullet proof and in my experience is always more reliable than electronic Fi.

The problem is, your saying that it has been tuned so timing should be correct and all the leads and plugs have been changed also. But it sounds like a firing problem more than anything else. Time to check everything that controls fuelling for this system. Dizzie, relays, breathing pipes, ignition coil and anything else that you can think of. Sorry I can't be of more help.

What dick-head in the garage thought that your car had a CAT on it? I have to say it sounds like they cocked up somehow with your car. Thinking that it had a CAT is a huge **** up by anyone standards, I don't even know of an 88 car with a CAT converter fitted as standard.

Taken from haynes an explanation of your fuelling system

"The continuous fuel injection is found on the B28E, B200e, and B230e engines. It is a well proven system with little to go wrong and no black boxes to worry about. As the name implies, fuel injection takes place continuously whilst the engine is running. The rate of injection is varied to suit the prevailing speed and load.

Fuel is drawn from the tank by the tank pump. It passes to the main fuel pump where the line pressure of around 5 bar is established. An accumilator next to the pump provides a reservoir of pressure to improve hot starting. From the accumilator the fuel passes through the filter and then to the fuel distributor on the top of the manifold.

The fuel distributor looks like an ignition distributor, but it has fuels lines instead of HT leads. There is one line per injector, with additional lines for the start injector and the control pressure regulator. The fuel disritbutor's main function is to regulate the fuel supply to the injectors in proportion to the incoming airflow. Incoming air deflectsd to the airflow sensor plate, which moves control plunger in the fuel disributor and so varies the supply to injectors. The airflow sensor and fuel distributor together are sometimes called the fuel control unit.

The control pressure regulator reduces the control pressure during warm-up and under conditions of low manifold vacuum, and so enriches the mixture. (A lower control pressure means that the airflow sensor plate is deflected further, and the quality of fuel injected is decreased.)

An electronically controlled start injector provides extra fuel during engine starting. A thermal time switch contorls the duration of start injector operation when the engine is cold; on a hot engine an impulse relay provides a smaller quantity of extra fuel to be injected. An auxillary air valve provides the extra air needed to maintain idle speed when the engine is cold. On models with the constant idle system, an air control valve takes the place of the auxillary air valve."

Hope it helped!

[146ken]

Hi
Thanks for that. I've been struggling with a u/s computer. Hopefully sorted and can get back to this problem which is still sat on the drive.
Now fuel supply is definitely okay so will check through your recommendations and get back. cheers

[146ken]

The fuel filter has been replaced today, it was pretty filthy in there an d some water as well. Tune-up guy/mechanic ( it says fuel injection specialist on t he side of his van, but I'll reserve judgement on that) had her running sweetly while standing on drive. Took her out for a test drive and problem reoccurs after about 5 minutes driving, juddering and then dies, no whoosh when petrol cap removed, main pump straining noise. Switch off ignition, restart she goes fine for about twenty seconds then repeats juddering etc. If she dies and ignition not turned off to stop pump then she won't restart.
Once left on the drive for an hour or so she will give another 5 minutes of smooth running.
Where next?

[146ken]

It is the B200E.

[madder93]

Try cleaning the throtle body inside with a carb cleaner[or even a throtle body cleaner]. You will be suprised what differance that can make. Check for air leaks around manifold.