MAP sensor

Good morning,
The MAP sensor that I bought from Canada arrived yesterday so its fitted, unfortunately the car still isn't running correctly, it no longer black smokes but it is only running on 2 cylinders , 1 and 4 are not firing, I've checked the basics, spark, compression, wiring from all injectors back to the ECU, different ECU pulse generator contact breakers, all the earths, injectors pulses with just a multi meter for voltage and still no joy.
Can anyone help me I'm losing my way what should I check next or what should I have checked that I haven't?
Thanks Doug.

Just been looking through the trigger contacts section and spotted that there are 2 groups that are controlled, group1 controls cylinders 1 and 4 and group 2 controls cylinders 2 and 3, it can't be a coincidence that my car won't fire 1 and 4 can it? I'm thinking it must be related to the trigger contacts although when I tested them both groups seemed to be switching!

Hi Doug,
you are right. Cylinder 1 and 4 are the same group.

But - you told us before you tried different pulse generators (trigger contact sets).

I think, you should try to interchange the outer contacts <the groups> at the generator unit to be sure.

Regards
Norbert

Just a quick update, the cause of the running on only two cylinders was spark plugs, even though they were actually sparking in open air I'm assuming that as soon as they were refitted they were unable to function in compressed air!
However now it is running on all four again it has returned to black smoking and running extremely rich is it only temp switches that control this!

Doug.

Hi Doug,
did you check the MPS?
A MPS with vacuum leak would lead to very rich mixture.

But check the resistance of the cylinder head temp sensor at the ECU connector, too. The other reason for rich mixture...
Check at the connector, not at the temp sensor, otherwise you wouldn't detect a wire connection problem.

Regards
Norbert

Good morning Norbert,

I'll check the cylinder head temp sensor next but I thought these sensors where just an overheat sensor in that as long as the temp didn't go above a specific value the engine continues to run.
I have accidently left this disconnected before and the engine won't even start I didn't realise that it affects the mixture.
I got 2 MAP sensors from Canada and they both make the engine behave the same, really rich, so maybe both don't hold vacuums I will also test these, I did electrically test them but not for vacuum.
I'll feed back on the above and let you know how I get on, thanks again Doug.

Hi Doug,
the temp sensors, the cylinderhead sensor more than the air temp sensor, are essential for 'calculating' the mixture.
When the cylinder head sensor is disconnected, the mixture is enriched as if the temperatures would be extremely low, the mixture is about 3 times richer than it should be when the engine is warm.

You could replace the sensor in the case it is defective by a simple resistor, about 200 Ohms (1/4 Watt is sufficient) against ground for a test.
Then the ECU 'calculates' the mixture for a warm engine.

I'm sure the disconnected sensor is the reason for your probs.

Regards
Norbert

Hi,

I was out for a family event so I could nto answer earlier. Engine temperature sensor is essential for mixture. If missing, your mixture can be three times as rich as normally. It heavily affects.

New MAP sensors should of course be checked for vacuum leak, no renewal of potting and original screws / rivets.

Volker and Norbert,

You are both absolutely correct the cylinder head temp sensor wasn't connected properly so I've replaced the connectors and reconnected it and the resistance measured at the ECU connector is as per the table and it now runs much better at idle, as I would expect.
I also checked the 2 replacement MAP sensors that I sourced from Canada for vacuum, 1 is good the other leaks down a bit too quick, not as fast as the one tested in the video clip on here but faster than the other, so the good one is fitted.
I managed to drive it down the road yesterday evening too but it won't pull under high load situations, it just misfires and splutters, could this be FI related or is it more likely to be the HT ignition system causing this?

Many thanks again gents for all your help.

Hi Doug,

it sounds more like wrong ignition timing if it misfires.

I'm already running as advanced as I can! Have you ever encountered these symptoms where the FI has been a cause?

Hi,

you cannot just put your ignition timing as early as possible. Those misfires will knock on your piston long before it reaches TDC and hit it.

What is your exhaust like with correct ignition timing? CO and HC if possible.

Hi,

Sorry no I don't have access to an exhaust gas analyser so I need to go to a garage to get CO and HC readings, could too far advanced cause a misfire do you think, I am running more than the manual says but it doesn't "pink" or pre-ignite I checked it whilst running the car on a rolling road dynamometer a couple of years ago.

Hi,

normally a misfiring in exhaust is unburned fuel from too late ignition or too much fuel as it could not be burned. You told us you pushed ignition timing to as much advanced as possible.

Hi,

Yes advanced not retarded, the manual suggests 0 degrees @850rpm I think but I set it at 3000rpm (max advance) which ends up at somewhere around 38 degrees BTDC that's about 10 degrees more than it should be but it was the only way I could get good driveability driving in town (low rpm on and off the throttle).

Hi,

you should start from engine mechanics basics: Valve timing and false air. A car that needs such igntion timing has serious other problems.

My next stage of investigation is to eliminate all of the H/T ignition system piece by piece and if after that it still misfires under load then I guess potentially I have mechanical problems!
Things like valve timing are difficult to check without complete engine dismantle and I've already done compression checks and discovered nothing to cause alarm - false air I have struggled to test with any success, historically when I've encountered air leaks they wont idle very smooth and mine idles good, but what ever I do next I'll feed back and try and close this thread.
Just to try and justify my reasoning for such advanced ignition timing, I have read something on a different forum that suggests that when an engine is running really rich you may need to advance the timing by anything up to 10 degrees to allow enough time for complete combustion of all the fuel, so maybe if I get to the point where I have cured the misfire I'll try reducing the ignition timing to reflect VW's intentions as now I've hopefully fixed the FI issues with a new MAP sensor and repaired temp sensor wiring so hopefully it isn't running too rich!

Thanks for all your help so far, Doug.

Hi,

Quick update on the above, I've replaced some of the HT ignition system with new parts with no success but I'm still waiting for the new distributor cap and rotor arm to arrive before I can say for definite that the cause is or isn't ignition related.
If the cause turns out to be mechanical internals worn out and I decide to re-build the engine does the D jet have enough scope to cope with either extra capacity or bigger cam shafts etc. to try and gain a little bit of power or should it just be re-built totally stock?

Thanks again Doug.

Hi,

as D-Jetronic is an open loop control system you should stay with stock versions.