Here's one for ya! 1993 850 cranks over,has a couple of sparks from coil and then nothing until you let the key go.The wave pattern from the cmp and crank sensors get dirty after the starter is engaged,but if i jump start the car (its a manual)it ALWAYS starts perfect.The computers have been checked,the sensors have been replaced,the harness in the engine bay was replaced (it had been soldered in a couple of places and when we jumped the wires in this harness it started fine,we thought we found the problem),volt test done on ignition switch and computer powers and ground,the fuse panel grounds and powers checked,the anti-theft relay exchanged,ground wire replaced and moved to starter bracket to block ,starter was replaced with factory unit in September and is ok as is battery.All grounds have been cleaned and checked .... I get 4 codes with the VST (Volvo Scan Tool)both cmp codes and both crank sensor codes but these units are ok as i said before(they have been changed and checked again)This problem showed up 2 years ago for a short time and i cleaned a few grounds then and the problem corrected itself.This problem has slowly started to show up again in the last year and is here now again.4 mechanics (2 are Volvo mechs.and 1 a GM training expert in electrical)have given me a hand with this in the past month + but we are all stumped.Any ideas would be gratefully appreciated.I have worked on Volvos since '85 and have NEVER had a car like this!!!

Ready to set fire to it ...pb90125

It's obviously electrical and also occurs often enough to duplicate SO it can be solved by systematically diagnosing the related circuits using a OEM Volvo wiring manual for your '93 850. One needs to trace it, what does/doesn't have proper voltage when it's not starting? A good technician can fix it but finding a guy willing to spend the time might not be easy. Most flat rate technicians don't enjoy spending alot of time on one car tracing electric circuits and not all techs are good at it.
Obviously you've had several people guessing but none have fixed it. Without seeing a car like that, I won't even guess from here.

I've heard that the wiring harness's on early 850s could rub though, short just above the steering column and that it could then cause strange electrical occurances but I can't say that I've seen that myself. To check, you'ld need to remove the upper dash pad and instrument cluster to visually inspect that harness.

It will take a very knowledgeable and dedicated Volvo tech to solve a problem like that but I do believe it can be fixed, not impossible.

I hate to sound like an idiot, but did you try a brand new battery?

I know it checks out OK, but if it starts fine on jump, then perhaps it has a surface charge but doesn't have the ass when you crank it. Additionally, clean the chassis grounds to everything that you doubt. Have you resistance checked the battery cables? That too would make some sense with the jump starting.

The volume of issues that I've seen on Volvo product due to voltage or resistance issues is large. (I wrench on a lot of Volvo product of various years). More often it is the SRS and ABS systems, but not excluding the EFI and ignition. Especially sensitive are the later models (not the rear-drive 4cyl ones). Frequently it's a battery or cable issue that starts the ball rolling. And not surprisingly, fixing either the battery, cable, or ground problem often straightens out the problem.

I don't mean to offend anyone's professional experience or expertise, but it's often really hard to consider every single avenue of repair when there are so many. There must be a logical answer. Also, that way you'll feel confident that you've tried everything before toss the match.
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Chris Herbst, near Chicago, IL. 93 940, 91 240, 90 240, 88 740, 87 240

What kind of voltage do you get from the donor car when you jump start the car?
Is the cranking speed higher when jumping? Is the compression good?

I had a '56 Ford that would start instantly if the battery was fully charged, but would not start at all if the battery was down at all. You could twist the key and let it go immediately and it would start if the battery was up.

I realize that this is not a parallel situation, but if it ALWAYS starts when you jump it, the problem has to do with something that the donor battery provides that the battery in the car does not. All the other stuff is window dressing.
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2 8s & 2 7s 700,000 miles total

When i said jump the car ..i meant pushing the car and popping the clutch,not boosting from another car.The compression is fine and that will not stop spark .
I have found alot of wiring fiascos over the years in all volvos but this one ....is incredible.We thought it was in the starting circuit,isolated it and checked again but still am getting bad signals from the cmp and crank sensor.it is not the computer,main harness,sensors,battery,ground cables. I have put in alot of my time and i've never given up but you can only work on this for so long and i was hoping anyone who reads this,no matter how silly a guess ,can give me any ideas.Sometimes you need a different angle on things.

I am in my 17th year as a volvo (specialist?after this car??) and this car is frustrating.We have volvo shop manuals,scan tools etc.. but this has to be something strange.I have inspected the harness inside the car,under the wiper cowling and everything checks out fine.If i do find the problem i will let you know. thanks