1994 850 - Refuse to start

vitos · Post by **vitos** » 22 Jun 2014, 09:19

Hi guys,

i've recently got a 94' 2.5l volvo 850 with "no spark" problem. As time proceeds and car still won't start, I might need some help and advice from real professionals.
Car cranks, fuel pump gives fuel, but it is not able to start due to lack of spark.

These are things I've found out about it.
1) Compression. There is compression about 11 bar at each cylinder, which is good. And thats why i guess running belt is correctly aligned too. (otherwise there will be no compression or the engine will be damaged)
2) Fuel pump is running, there is fuel in rail.
3) Injectors are working, spark plugs are dirty by fuel and i can smell fuel too.
4) Wiring between rpm sensor and camshaft sensor and ECU are ok.
5) RPM sensor generates signal, camshaft sensor generates signal too. I measured it by oscilloscope and it looked fine.
6) Coil and power stage works ok when controlled by pulse generator that simulates ECU pulses, so it is in good shape too.
7) distributor and rotor look a bit messy, but when attached to coil with simulated control signal, it generated spark without problem.
8 ) engine swap - it looks like previous owner swapped engine by one from volvo V70. Could it even be swapped with no major changes?
9) there are no fault codes in ECU

Now it looks like ECU is the reason of these problems. However, I also measured coil control signal and according to it, it looks that ECU is controling ignition coil
correctly (spark is generated) but at wrong moment. It seemes that coil control signal from ECU is 90° advanced to TDC of cylinder.
That 90° advantage also means, that ignition pulse of 1st cylinder is perfectly aligned with flywheel mark. But I read somewhere, that flywheel mark should be visible through starter motor hole when 1st cylinder TDC, right?

Now It's obvious why there is no spark. Coil generates one, but thanks to this spark "advance" it can't go throught distributor which is not aligned with proper spark cable yet.

So, question is, what could cause ECU to act like this? At first i thought about crankshaft and camshaft alignment, but i'm not able to find any volvo 850/70 waveforms to compare it with.
Is there anybody who has some of these waveforms, or anybody able to measure this things on his/her Volvo?

As I checked my measurements, flywheel mark is 90° advanced before TDC of first cylinder, so it could be ok, right? What about camshaft, does anybody know what rising and falling edge of camshaft signal should be aligned to?

Hope I wrote it clearly for you to understand, thanks in advance for all guesses.

Here I attach some waveforms, hope it is understandable.

http://imageshack.com/a/img820/1664/pwzy.png

http://imageshack.com/a/img819/3944/sp7o.png

Post by **erikv11** » 22 Jun 2014, 09:48

Are the plug wires attached in the correct order?

from https://www.matthewsvolvosite.com/forums ... =1&t=31425

Post by **rspi** » 22 Jun 2014, 10:49

I have read where people had issues with these cars starting after motor replacement due to poor ground between the block and tranny. They failed to clean the matting surfaces real good and the car did NOT get a good enough ground.

vitos · Post by **vitos** » 22 Jun 2014, 14:35

Hi, thanks all of you for reply.
All cables are in the correct order, I checked it for many times

. Problem is, that ECU tells coil to put spark, but at wrong time. It is a bit noticeable from first waveform I've posted.

Even if there will be no distributor, and spark will go right from coil to cylinder, it will put spark 90° before TDC that means at the end of intake stroke.

MrGruffles · Post by **MrGruffles** » 23 Jun 2014, 11:45

Hi, You mentioned that the previous owner had possibly swapped in an engine from a later model: was the ECU/ECM swapped as well? I believe that it has to be from a compatible model, which may also vary by model year. I'm guessing the ECU/ECM for the original 1994 engine used a Motronics 4.3 system but don't know offhand the changeover year to Motronics 4.4.

Also, If the later engine requires a direct ignition system control module, then there should be an additional computer underhood (for a total of two if manual shift or three if automatic.)

vitos · Post by **vitos** » 23 Jun 2014, 14:11

Hi,

I guess there is still an old injection and ignition control as it was. I suppose that previous owner had changed hardware only, and left whole electronics stuff intact. Because wiring harness seems to be dismantled and than rebuilt back.

There are still two control units (ignition and injection) under the hood. I read somewhere that 1994 volvo has LH 3.2 not Motronic 4.2 but I don't know the difference between them. Only thing I can do is find out and tell you part numbers of those two units, maybe you'll be able to decide what engine management do I realy have there.

vitos · Post by **vitos** » 23 Jun 2014, 14:16

rspi wrote:I have read where people had issues with these cars starting after motor replacement due to poor ground between the block and tranny. They failed to clean the matting surfaces real good and the car did NOT get a good enough ground.

At first I thought so too, so I measured voltage between battery + various places on the engine itself and it gave me 12,5V all the time. So I think there is no poor ground, but I'll double check it, just in case

.

Post by **Ozark Lee** » 23 Jun 2014, 15:23

The grounds for the ECU(s) bolt up to the block separate from the main ground cable. They are bundles of small black wires that mate up to the block in the area around the starter. They are easy to overlook when an engine has been swapped out.

The 1994 non turbo cars usually have the Jetronic LH 3.2 system that has two modules, one for fuel and one for ignition. The codes are read from both port A-2 and Port A-6 on the on board diagnostics.

If you have the LH 3.2 system then there are two modules in the cage with a manual transmission and three modules with an automatic transmission.

Have you checked the orientation of the camshaft position sensor. When your spark is 90 degrees out of sync it suggests that the sensor isn't properly indexed. It is possible to bolt it on incorrectly but you almost need to try to get it wrong. That said, it has happened so make sure that the index tab is properly seated on the end of the exhaust camshaft.

...Lee

MrGruffles · Post by **MrGruffles** » 25 Jun 2014, 11:51

Ozark Lee wrote: The 1994 non turbo cars usually have the Jetronic LH 3.2 system that has two modules, one for fuel and one for ignition. The codes are read from both port A-2 and Port A-6 on the on board diagnostics.
...Lee

Thanks for the correction: I sometimes forget some of the N/A vs. turbo differences!

vitos · Post by **vitos** » 25 Jun 2014, 12:54

Ozark Lee wrote:The grounds for the ECU(s) bolt up to the block separate from the main ground cable. They are bundles of small black wires that mate up to the block in the area around the starter. They are easy to overlook when an engine has been swapped out.

The 1994 non turbo cars usually have the Jetronic LH 3.2 system that has two modules, one for fuel and one for ignition. The codes are read from both port A-2 and Port A-6 on the on board diagnostics.

If you have the LH 3.2 system then there are two modules in the cage with a manual transmission and three modules with an automatic transmission.

Have you checked the orientation of the camshaft position sensor. When your spark is 90 degrees out of sync it suggests that the sensor isn't properly indexed. It is possible to bolt it on incorrectly but you almost need to try to get it wrong. That said, it has happened so make sure that the index tab is properly seated on the end of the exhaust camshaft.

...Lee

Thanks for advices. I'll check and clean those ground wires you mentioned, and check position of camshaft sensor on weekend. Even if I'm almost sure,that the sensor is correctly oriented.

My guess, is it possible to turn 180° that camshaft shutter inside the camshaft sensor housing?