Hi all,

Yesterday I did a compression test on my 1.4 16v engine, as i am suffering from some power loss and wanted to rule the cylinders and pistons out. To do this test, it was suggested that i should unplug the injectors, which i did, and I removed the coil packs and spark plugs. I completely removed the coil packs and unplugged all 4.

However, once reassembled and double checking everything was plugged in, my engine will crank but there appears to be no spark at all on any cylinder. We've checked for spark on all 4 plugs by holding against the block and cranking. We've checked for a 12v to each coil pack, and each of them receives 12v, but will not spark no matter what.

My car uses a Magnetti Marelli 4TV ECU, which apparently has common faults relating to ignition and i've read about problems with signal to ignition coils.

Does anyone have any suggestions or experience with this?

Thanks all

You may have blown a fuse when removing coil packs etc. Not sure which one on yours but look at the ones near battery box as well.

Alasdair

On 22/04/2026 at 11:41, Alasdair1 said:

You may have blown a fuse when removing coil packs etc. Not sure which one on yours but look at the ones near battery box as well.

Alasdair

Thanks for replying and sorry for the late reply. All fuses have been checked , we’ve had a new ecu. A mobile diagnostics has been out and diagnosed as the crank sensor, however we have rpm reading on dash and this goes away when sensor is unplugged, also replaced sensor twice and replaced cam sensor. All sensors have 5v trace and ground. Still no spark or fuel at all when cranking. Any ideas are appreciated , thank you !!

Edited 5 May5 May by Obate2

If you have had a new ecu wonder if its an imobilser problem? Had one stick on on my old seat diesel. On diesel they start and then stop but on petrol I think they just don't start. Not exactly sure how to check. There may be a relay for the ECU that has failed as well.

Alasdair

I'd be tempted to grab a set of scrapyard coilpacks to try.

(Or a friend with a similar engine who would let you test yours one by one in their car, as a free test?)

I read some time ago that it's quite easy to kill these things by trying to see if you have a spark with the plugs not mounted in the engine. Not sure I understand the mechanism, but a quick and easy thing to try (with everything fully mounted!).

Edited 6 May6 May by Breezy_Pete

An after thought might be the earth to coil packs. When you checked voltage to them did you check the continuity of earth or use engine block as -ve.

10 hours ago, Breezy_Pete said:

I'd be tempted to grab a set of scrapyard coilpacks to try.

(Or a friend with a similar engine who would let you test yours one by one in their car, as a free test?)

I read some time ago that it's quite easy to kill these things by trying to see if you have a spark with the plugs not mounted in the engine. Not sure I understand the mechanism, but a quick and easy thing to try (with everything fully mounted!).

Hi thanks for replying, unfortunately I don’t think this would make a difference, as when reading OBD channels when cranking, the ecu is simply not outputting any injector pulses and has 0 ignition angle, ie no spark. I’m really not sure where to go from here, even our diagnostics man is stumped. Oscilloscope has been out and crank signal is present.

Does sound like an ecu problem. If the ecu is getting power but not puting out a signal it may have failed internally unless its a wiring isssue. Not sure if they are repairable or a new one is available and old one could be copied to it or perhaps a second had one but it would need to be programmed with data on the original

Alasdair

5 minutes ago, Alasdair1 said:

Does sound like an ecu problem. If the ecu is getting power but not puting out a signal it may have failed internally unless its a wiring isssue. Not sure if they are repairable or a new one is available and old one could be copied to it or perhaps a second had one but it would need to be programmed with data on the original

Alasdair

Hi thanks for replying again, it’s had a new ecu copied from the old one with data and still no difference

I take it it was the same problem with old ecu. If so wonder if the problem has been copied to new one as in a software issue/corrupted data on the original. May need special diagnostic tools to check. I take it there is no sign of imobilser active symbol on dash when cranking and is it there pre ignition? just in case bulb/led has failed.

Alasdair

Just now, Alasdair1 said:

I take it it was the same problem with old ecu. If so wonder if the problem has been copied to new one as in a software issue/corrupted data on the original. May need special diagnostic tools to check. I take it there is no sign of imobilser active symbol on dash when cranking and is it there pre ignition? just in case bulb/led has failed.

Alasdair

Yes , the light comes on with ignition and goes out soon after . That is a good point , and I’ll have to research about software issues / corrupt data.

Was the hardware number on the old ECU an exact match for the new one. Hope you get it sorted.

Alasdair

9 hours ago, Alasdair1 said:

Was the hardware number on the old ECU an exact match for the new one. Hope you get it sorted.

Alasdair

Hi, yes it was a direct match. So diagnostics has been back out today, confirmed cam and crank signal. He plugged in obd reader and could not get a vin out of the ecu, which led him to can bus faults. Resistance check across can bus with nothing coming back, so there’s my problem. Thank you for all your comments

16 hours ago, Alasdair1 said:

Was the hardware number on the old ECU an exact match for the new one. Hope you get it sorted.

Alasdair

Glad your getting somewhere.

Alasdair