Hi All, I have recently acquired a '95 850 turbo sedan. The previous owner replaced the motor with a used motor with 60k miles. He was unable to get the car running due to a crank no spark situation. I am getting no spark at the coil.
The cam sensor and crank sensor and coil are all new, I have tested them according to the directions in the Chilton manual and believe the sensors and the wiring to the ECM to be good.
When I test the ignition coil terminal #1 (blue wire) while cranking, I get 10v. I believe it should be between 0.7-1.3v so it seems way off.
Also, when I test the power stage control plug at terminal 4, I get 0.3V where it should also be 0.7-1.3.
I tried a spare ECM which I believe to be good, and still no spark.
If anybody can point me in the right direction it would be greatly appreciated.

 

10 volts at the coil sounds good to me. I hadn't really thought about it, but that normal for just about any other car anyway.

There have been a ton of problems with the main fuel injection relay plug. The plug internals were made out of some gummy material that all disintegrates and they won't plug up properly. When you swap engines, you are likely to unplug that and that does cause a no spark. it powers a few pins on the ECU as well as the hot side of the fuel injectors.

 

Thanks for the input!
It’s possible that the plug is bad. I took a good look at it and found cracks in the insulation of the wires leading to the plug.
However I did test all 4 plug connections for continuity to the next point down in the harness. The wires seem good and the plug connector looks ok. I had healthy battery voltage at the two red wires. Interesting that the orange/black wire goes to the TCU.
I have read conflicting info on whether the fuel injection relay (the one over the fan) will prevent spark. I should probably repair the wiring but that entails replacing the plug. I’ve read a few threads about different solutions, I’m sure I can come up with something. I just don’t think it’s the issue but it can’t hurt to repair an obviously potential problem.
For a Hail Mary I’m going to try a TCU and a used Bosch camshaft sensor I got off eBay for cheap. The camshaft sensor on the car is unbranded. I at least want to try a known good one before I rule it out. As far as the TCU, well, there was that one guy on the internet who changed his and it worked. So for $16 I’ll give it a try.

 

I am an experimenter, so if there's any question about whether or not you have fuel injector power, just jumper power to that. You can do that for free.

I don't do any parts cannonneering ever, so that is my perspective. Some (a lot) of the car is subject to free testing, but if you look at factory diagnostics, you'll quickly come to the place where they pull out a breakout box, and you'll probably never have that.

On an 85 turbo, you should have motronic 4.3 with both OBDII and the telephone switchboard under the hood, so you have fabulous diagnostic capability if you know how to use it. What's your status on that? Do you need instruction?

You might poke around here:
https://www.volvoclub.org.uk/volvo_w...techdocs.shtml

There is a doc there that addresses no-start really well, but it's hard to find by name. The name is ECU Testing - non Turbo even though you have a turbo, there is a little extra information in there and you need to look at both of them. This has instruction about ohming out the crank sensor, which is the best you can do, and direct testing of the cam sensor. The OBDI capability on the 95 also includes having the ECU test the crank sensor. At least I think it will.

If the OBDI switchboard does not work, and you just get a dim LED that won't flash, that was for me an indication that the fuel injection relay was unplugged.

 

I'm at a loss. I followed the directions on this thread which isn't for my 4.3 system but I think should be similar.
https://www.justanswer.com/volvo/3bz...k-replace.html
After cranking for a while I was able to get a code from the obd2 port- p0120 Throttle position A circuit
From the self diagnostic box in the engine with the blinking led, I got code 111 from port 2 (no fault). At the A1 port, I got 223 TPS signal low
and the A7 port, code 122 temp sensor interval too long
Would throttle position sensor or temp sensor prevent spark?

I cleaned up the fuel injector relay wires and plug and feel I can rule the connector out. When the key is turned to the on (not start) position I can feel a healthy click at the fuel injector relay.

 

There are lots of reason why you might have no codes and no spark, of course. I use a scan tool. Do you have one? I don't really use codes much. They are just not meaningful enough. With a scan tool, you can investigate the throttle position feedback all you want, and you can see what temperature the PCM thinks. I don't know if the TPS would cause a no start, but I guess I could figure that out. I could unplug mine and see if it would run.

The next step to me would be this. For free, I would try to decide whether or not the PCM was triggering the coil. This is a yes or no thing. A tachometer should be adequate for that. Triggering the coil manually would also be enlightening (literally) and also free. Like you, I suspect PCM is "bad" and the ignition system is "good" but no need to take a chance.

I personally don't know why there is that electronic component, whatever it is, between the coil and the PCM. I don't know what that thing does. That concerns me mildly when I am dealing with a no start.

There is another thing to consider. There used to be, or is, this 'story' that people swapped engines and got a no start, and the solution was to swap engines again (let's call that the "microsoft" engine swap.) This is total nonsense, and so there must have been some reason for that. A reason has emerged that might explain it, maybe. It was suggested that the power cable running to the starter was interfering with the crank signal. If the crank signal was muddled, that is an example of something that would be easy to see with a scantool.

 

btw, there are two very important relays on the 850s - the fuel pressure relay (easy enough to find in the upper relay box) and the fuel injector relay which sits under the cowling above the radiator (should be gray). As to the no spark, if you have issues with component like the crank position sensor etc that would be problematic. Temp sensors really only impact the fuel mix and I have no idea what role (if any) the throttle position sensor would have with spark (other than possibly advancing the timing?) and not sure it ifs even in play during start up.... I'm with FBP that you need to do some more testing and scanning. You may want to check out volvotips.com as there's some useful documentation on the 850s there.

 

Thanks for the replies. I have tested everything I can with a multi-meter. The one erroneous reading I get is that both the red and blue wires at the coil have battery voltage while cranking. I believe the blue wire should have less voltage. I tried the test where I removed the blue wire from the coil and grounded that terminal at the coil and still no spark. Would this indicate a bad coil? Any thoughts would be appreciated.
I'm taking it in ti a Volvo specialist in town on Tuesday. I will report back with any findings.

 

I brought the car to have somebody look at it as I was at a loss. Unfortunately, they did the same tests I had already done and 100 dollars later were unable to get me any closer to the answer. They seem to think there is a broken wire in the harness. They also suggested that I check that the timing belt is lined up correctly, they seemed to think that that could throw off the signals.
As it stands there is no spark and no injector pulse.
All of the relays, and fuses check out.
Cam and crank signals are present.
Power and grounds are good.

When I get the car back I'm going to check the timing, I'm also going to take another look at the relay plug above the fan, and then search for broken wires.

 

I checked the timing and found the intake cam off about one tooth (timing belt was replaced when engine was swapped). My cam sprockets have no discernible marks on them. I had to remove the cam sensor on the exhaust side, and the cap, rotor, from the intake side. With the crank aligned at the mark and verified at the #1 cylinder the exhaust cam was lined up properly with the groove parallel and below the valve cover seam. However, I would estimate that the intake cam is about one tooth off.
This is an obvious problem, and unacceptable. I would definitely need to fix this before proceeding.
My question is, would this prevent spark and injector pulse? How would the computer know the intake timing is off as there is no sensor (that I know of) attached to it?


This is the exhaust cam from the rear. lined up properly.







This is the intake cam from the rear. I would estimate about one tooth off.

It wont cost me anything to get the timing right but, I'm not confident it will address the no spark issue. Thoughts?

 

I wouldn't think so, but I could sure be wrong.

 

Timing fixed, a little trouble getting the belt over the tensioner, but I managed. As expected, there was no change, but a potential issue addressed.
I had a funny exchange with a shop in town today. They very politely said "no thanks" when I asked them if they would be willing to take a crack at it. Super nice guys and I laughed, but maybe it's a sign...
It doesn't make any sense. It cranks over strong, and ran before the engine swap. Both fuel relays are working, The wiring has continuity to the ecu, grounds are good. I have communication at the obd 2 and the blink codes. Even the radio works when I enter the code, Windows locks, blower, etc.
Not really sure where to go.

 

My battery tested bad at the auto parts store. It has enough juice to crank the engine a few times. Would this cause a no spark situation?

 

It might. If you have a dead cell then you would have 10 volts at rest and then you might be cranking with 8 volts approximately. Electronics don't tolerate that too well.

 

I got a good battery to test but still no luck.
I had somebody come by with a good scan tool. With they key on, I can communicate with the ECU, but as soon as I engage the starter, the scan tool loses connection. Why would this happen? It leads me to believe that it may be related to my no spark no pulse issue.

 

Unusually low voltage? Volt meters are cheap. In fact, they give them away free at harbor freight.

If the PCM is losing its power supply on cranking, then you need to know that. Because that is going to be super easy to fix, and there are lots of easy ways to troubleshoot and experiment on that as well. For example, You can power the starter easily without turning the key. If that starts it, you shall have found your problem. But keep in mind that is just one example.

 

This shows the voltage vs rpm
I hooked up my WiFi scanner and got this reading. Indicating that the voltage is dropping below 10volts. I have read that this could be a problem.