Hi i just installed a 1.3 mpi engine ( which had not been running for a while) that has only 31,000 kilometers with its original harness and ecu into a skoda favorit.

 

It starts but i'm having some problems.

 

At idle the two middle cylinders are not firing but as it picks up the revs they start working fine.

 

I found out that its the two middle cylinders because i unplugged the injectors and noticed that the engine behaved the same.

 

At first i thought that the injectors where dirty so i put some injector cleaner and ran the engine with it for a few days to no avail.

 

I then switched the places of two injectors ( one of which i knew that it was working ) and the problem stayed the same.

 

I also changed the plugs and put new ones but it still isn't working fine..

 

I sprayed carb cleaner into the throttle body too.

 

if i leave the engine revved at about 2,000 revs, most of the time the engine would start to work on all 4 cylinders... 

 

its a strange problem and from the looks of it not a very common one :/

 

Can anyone help me identify or suggest something that i can do to fix the problem?

 

Thanks a lot in advance for helping me!

If it's not fuel related, there are 3 other possibilities: spark, timing or compression. I would check first the command signal for ignition transformer (31 on schematic below). If you're lucky you have a bad ground at pin 4.

 

If you're lucky you have a bad ground at pin 4.

Correction: Disregard this part.

Better look for signs of corrosion inside ignition transformer (IT) 4-pin connector.

 

Anyway, the quickest method to diagnose your problem is to stick two T-pins in the back of the IT connector (pins 2 and 3) and look at signals with an oscilloscope (preferably with 2 channels). If they have the proper amplitude and timing, you have a bad IT. If signals are not good, you have a bad ECU.

 

Of course, not anybody has an oscilloscope at hand. In that case, try replacing the IT with a known good one and see what you got.

Hi thanks for your replies.

 

to better describe the situation... atm the car is stripped and the wiring is just placed.. the grounds are all secured apart from the one of the window winders.

 

While i was plugging the plugs for the engine to run i put some Vaseline ( since i was told that it helps ). 

 

Given that you told us that it might be a bad ground we sprayed contact cleaner on all the plugs..

 

while i was cleaning the plugs i noticed that one of the plugs of the sensor that is located in the lower part of the induction one of its pins is corroded...

 

After we cleaned we noticed that it began running on three pistons at idle but not always and at one point in time, there was even a sign that the last piston was trying to fire.. but now its back to where it started firing with 2 pistons at idle.

 

Another thing that i'm a little concerned, is the fact that i changed the gearbox with one of a Favorit (since the original gearbox was off a Felicia and had different mounting points ). Could it be that the crank positioning sensor is out of place? 

 

If i plug the diagnostic cable will i be able to find out what is wrong and get any error messages from the software  to identify the problem? 

 

Thanks a lot for your patience.

The only grease I know it's used on a car's electric system is the dielectric grease, especially inside the rubber boot of the spark plug cables. I normally spray connector contacts with WD-40 (WD stands for Water Displacement) that cleans and protects in one step. 

 

Given the fact that the wire harness stayed a long time more or less exposed to elements and you felt a change while playing with IT connector, I recommend doing a more thorough cleaning job on ECU connectors. Spray WD-40 inside connectors, let it soak a minute then wipe the excess. Run the engine and if that Miss Fire is still present, begin wiggling wires one by one to catch any intermittent your wiring might have. If still no luck, as I said before, inspect and/or change IT.

 

From my knowledge, Favorit and Felicia gearbox is virtually the same, except mountings and some outside reinforcement ribs. But crankshaft sensor wise, I don't see why the ignition system would fire correctly for #1 and #4 cylinder and not for #2 and #3, unless ECU memory is corrupted.

 

You can use a VAG-COM to see if you have a DTC stored. Then clear them and repeat reading after running and stopping the engine twice. Keep us posted.

Edited 18 September, 201312 yr by adurer

Hi thanks for the suggestions  today i decided to take out the crankshaft sensor and see if its clean. 

 

I noticed that it had some dents in it ( possibly when we were installing the gearbox) and we are suspecting that it might be the cause to the problem.

 

unfortunately the part number is not available at the nearest store  so i thankfully i have found many being sold on ebay and i might borrow one just to test it...

 

fingers crossed

Hi i finally found the problem!! i managed to acquire a second hand coil for the plugs and replaced it and it  started right up with no problems to report so far finally i can move on and finish the car!!  

 

i was surprised as the faulty coil had only done 30k kilometers but at least i fixed the problem now 

 

Thanks a lot for your patience !!!!

Well done! Can you cut the rivets of the faulty Ignition Transformer (coil for the plugs how you call it) and open it?

It would be interesting for all of us to see what is inside and what failed.