I'd first like to introduce myself since I'm new to the forum. My name is Dylan and I've done quite a bit of reading on this forum. About two months ago my buddy bought a '93 850 with a "no spark" condition. I'll start off by saying this car has been through 5 owners with this issue and we bought it for $200 with two big boxes full of electrical components. The car is 100% rust free and the only real cosmetic damage is a basketball sized dent in the hood from a prior owner, and that the drivers eat is in rough shape. It also only has 120,000 on it as well, so I'd hate to see it go to a scrap yard. When we got it, we started by disarming the security system. Apparently the battery had gone dead and yada yada and when they put in a new battery it wouldn't even crank over. Once we got it cranking we still had a no spark issue, so we started with the basics. Replaced the plugs, spec'd out all of the plug wires and wire running from the coil to the distributor. Inspected the cap and rotor (they were brand new, but for some reason we had continuity between the post that the coil wire runs to and all of the contacts for the rotor, so I swapped that out with a good cap and we rolled it over and bam, we had spark, or so we thought. It was late so we went in for the night at that point and when we came back out the next day didn't have spark. Well, after cranking it over about 6-10 times we had another spark and then nothing. We realized then that we had intermittent spark, so we went to work specing everything out. We specs out all 4 of the CMP's that came with the car and they all tested good, even went and bought another brand new one to try just for the record with the same results. Spec'd out the CKP and it ohms out at 315ish which is well within spec in either direction and pulls 30 VAC when turning the engine over. Replaced the coil with a known good coil and the same story. I tried checking continuity throughout the wiring harnesses to the ECMs, but unfortunately I can't figure out the pin out number/lettering procedure and the chilton manual that came with the car doesn't explain it and I can't find a diagram for those setup online. Today, I decided to hop back at it and re tested the CMP and CKP, I then found that the ground going from the CMP back to the ECM which is shared with a couple of other sensors is at 7 ohms when according to the manual I should not be as high as 1 ohm. I ran a separate (good) ground to it and tried that with no luck. I wasn't sure if that was going to work or not since it didn't run into the ECM. Anyways, I've already gone through and cleaned up all of the grounds right near the battery tray and the one back on the firewall. I also am not getting any continuity at all for the coolant temp sensor. I don't believe that would cause a no spark/intermittent issue, but maybe? I'm sure there are things that I've done/checked that I forgot to list, but please understand, I've got well over 30 hours of experimenting, parts swapping, and electrical testing into this car and can't figure out which way to turn at this point, so any input would be greatly appreciated. I haven't found another thread yet where somebody has claimed to have intermittent spark like this, just that it comes and goes for a while, not a quick blip of spark and then nothing. If there is anything anybody can think of at all, no matter how stupid it may sound, please let me know!

 

One difficulty with this sort of case is that none of us has a breakout box, so once you get into checking individual wires to the ECM, you are really held back. The dealers could do it more easily with the breakout box. The truth is you really don't know for sure that's where the problem lies.

That said, I have found that these cars produce a weak spark to begin with, so it's not that easy to be sure what you've got. If I was working on that I might try to get it to run on ether, just to be extra sure.

One issue that causes intermittent spark in my experience is the fuel injection relay plug may rot internally and then you'll bump that accidentally and it'll start running. Then you bump it again and it stops. Make sure that is not your problem, the plug and the relay. It powers several pins on the ECM.

Does this car have the OBD diagnostic rig under the hood? Does it work? If so, there are some codes that ought to be set while cranking. The temperature sensor code would set if it's totally out of range. Crank or cam sensor code would set I believe if it sees the cam sensor blinking but not any rpms, or vice versa. I think that would set.

I have a 95 NA with what I presume is the same engine controls, but it's pretty reliable, so I am not 100% sure what codes it can set when it's not running.

P.S. Where do you live? Maybe you get some other perspectives on it. I find it 100 times easier to troubleshoot no start if I have another car there just like it that runs.

 

Fire bird parts, thanks for the reply! I may be wrong, but I don't believe it would be the fuel injection relay. One of the very funky things that I forgot to mention earlier is that the fuel injection still works just fine. I'm not sure wether it's injecting the proper amount of fuel for air at this point, but it is for sure injecting fuel. Typically also, when we do get that blip of spark the engine will fire right up though in all cylinders because we have a inline spark tester. So I don't see flooding being an issue. And when the spark does appear it's not by any means weak. It's a nice bright blue, but it's just there and gone. Now that you mention a relay though, it almost does seem like that is a strong possibility of what could be causing this though since when we do have spark it is a nice and bright spark. Well live in the mid Michigan area, Clio to be exact if anybody has heard of it. You don't see too many of these 850's rolling around our area, or volvos in general for that matter. To be honest, I've never personally checked the OBD 1. I didn't really know how until I looked it up last night, and I forgot all about doing it today too. My buddy has checked it and said he just came back with a 1-1-1, but I don't believe everything he says. He may have done something wrong, or just not payed close enough attention and instead of doing it again, just fed me a line of crap. So next time I get over to the car, which may be before the nights over I'll look into checking the codes.

 

have you tried re-enabling the alarm system? Not sure about the 93s but on newer models the alarm module has a battery in it that needs to be replaced from time to time. I'm wondering if your disabling the alarm has actually cut the input into the ECU so no signal to start.

 

According to my friend who is working on it with me, he says that he bypassed the alarm and that it's pinned. He says this one is purely a relay and requires no batteries. I'm not sure on that myself as I had nothing to do with that process, but I believe him on that because it's actually cranking over by the key now. I did get a 3-1-4 trouble code for the CMP signal. I k kw the sensor itself is good, but the ground going back to the ECM is at 7 ohms when the manual I have says it should be at or near 0 ohms. Is there a way without having to trace the wire right back to the WCMS that I can do a continuity check and see if it's that wire or the main ECM ground?

 

you may take a look at volvowiringdiagrams.com to see if they have the '93. Another good resource I use is volvotips.com I think the 3-1-4 is pointing to the cam position sensor... which could cause a no start...

 

I have all of the wiring diagrams for the car, I was just asking how to locate certain pins for the ECM so I can do continuity checks through the wires because the ground wire that runs from the harness plug for the cam position sensor back to the ECM is out of spec and id like to find out what's causing the issue. Plus, I could then check the common ground for the ECM itself if I could do that. For example, the ground wire for the cam position sensor is A18 for the motto if 4.3 ECM. I don't know how to locate that specific pin in the ECM mounting base. Then, that same ECMs common ground is pin A42. They list the order for the pinouts for fords and other vehicles with an ECM setup like this, but I haven't been able to find one for the Volvo.

 

I was assuming this car would be Jetronic with separate computers for ignition and fuel. What do you say?

 

It is. That's what stumps me on this manual. I also found the other night after peeling the harness back a ways that the CMP sensor wires from the plug to the ECM aren't the correct color according to the manual. The wires on the car are grey/red green/red and brown. And those aren't the proper colors according to the manual. I can find where anybody has spliced in a new connector and like I said, the wires stay that color as far back in the harness as I can see.