Low RPM misfire

[volvy740]

Tested the throttle position sensor. It clicks on and off okay as the throttle is moved off idle and back again. Readings were 4.9 volts with the throttle open and 0.1 closed.

Took the injectors out and they look fine. Sprayed them through with cleaner. Not sure how to judge their internal condition though...guess I'd have to send them to be sonic cleaned to be sure. Having thought about it, wouldn't the car run badly all the time and across the rev range if it was the injectors? It's the Bosch Jetronic continuous injection type, if anyone was wondering.

[Diesel-do-nicely]

Hi, the bosch jetronic injectors are easy to test.
1, pull all four injectors out of the head, get 4 jam jars , put them in the jars, get a large bucket of water ready, by your side in case the worst happens (fire) and unplug the 5th injector.
Have the assistant turn the engine over and observe the spray pattern, it should be a fine mist, no random sideways jets or irregular "haggs teeth" .
The problems will show up at idle the most.
Flat out the engine turbulance helps atomise a poor spray pattern to some extent.
SONIC CLEANING IS A WASTE OF MONEY , injector cleaner is also nonsence, these items wear out , i have cut old ones into bits to prove to sceptical owners and fans of cure in a can that the fuel flow cuts its own troughs.
New injectors are cheap, the service life is 80 to a very maximum 120 thousand miles.
New injectors will pay for themselves at about £1.50 per £10 used.
If you have any further questions ask me as i worked on the jetronics for 15 years .
Also, if the butterfly bypass port that the idle mixture screw controls is full of gunk, it will need cleaned out.

[Diesel-do-nicely]

A little more info for you, at idle the injector will be open very slightly, and any wear or damage will be amplified as the spring is pushed back to open a hairs width, at full throttle the tip is fully back and there is much less disruption to the flow.
0 437 502 015 is the number to look for.
Go scrappy hunting, porsch 924 , most vws and audis 1978 to 1986 . all use these and sometimes an audi will have a newish set.
If all else fails i will get you a price, but it will be around £140 inc post.
No sonic cleaner will ever say nah, these are shot, dont bother paying me to clean them, that does not pay the bills.
If the injector top is the small threaded one on a golf gti 16v for instance, the stainless steel hoses will still fit your car at the dis unit banjos, as they are all the same, and golf gti 1800 16v injectors were what i used in the 8v 1600 production class for racing as the spray pattern was better for more "crisp" throttle response.

[volvy740]

No fuel came out of the injectors when I tested them :s

It really confused me - the car has plenty of fuel and just half an hour earlier did a trip to Sainsbury's without any starting issues. I made 10mm holes in the jar lids and put the injectors through, securing them with an elastic band. The cold start injector was already disconnected. I took a picture of the set up, but it keeps saying "upload failed" when I try to attach it to the post. I'm sure you get the idea of what it looked like anyway.

Am I missing something? Honestly, I'm completely baffled by that result.

[Diesel-do-nicely]

ok, so your problem is very low fuel pressure , i assume the fuel pump could be heard whirring away . ?

[volvy740]

Yes, although I could only hear it with the car running (no priming buzz when ignition is turned on).

[volvy740]

Replaced fuel filter - no difference.

Whilst under there I noticed another canister in between the pump and the filter. Anyone know what it is? Just to re-emphasis the point, the pump isn't making a priming buzz when I turn the ignition on. It's suppose to though, isn't it? The pump itself seems rather noisy with the engine running. A final observation is that the pump whine changes pitch when the car stumbles/misfires. I'll have a look for a pump relay to see it that's up to anything goofy.

[stephend]

No, I don't think the pump is supposed to make a priming buzz - leastways, mine doesn't, or not that I've ever heard. On mine, you can hear the in-tank pump whirring faintly if you put your ear to the petrol filler pipe with the engine running, and you can hear the main pump as a low moaning sound from inside the car, again with the engine running. Hope that helps a bit.

[volvy740]

So, it has two pumps? This is news to me.

[stephend]

Originally Posted by volvy740

So, it has two pumps? This is news to me.

Yours is a B230E, i.e. K-jetronic mechanical fuel injection, right? Then yes, there's a lift pump situated inside the tank, and a main pump slung on a cradle under the floor.