I have an 87 - 740. I bought the car about 3 years ago and had a lot of problems when I first got it. For example, it shut off and would not start. The wiring harness had a lot of wires with melted insulation shorting out. The main wire that was apparently getting hot then was the green - red wire for the fuel system/ injectors. I got it running again and had problems again several times and finally it ran great after that; until now.

The other day I was sitting in traffic and it just shut off. It would start back up and go a few feet and shut off again. I did that many times, as I was hoping it might just be some water in the fuel or something, but it wouldn't stay running so I had it towed home. I didn't mess with it for a couple weeks. It thought for sure it was fuel related and used my manual and went through the tests. I replaced the fuel filter. I took the fuel pump relay off and jumped across to see if I could here the fuel pump run and it did (but I still don't know if both of them run). I went ahead and sprayed some starting fluid in the intake, just to confim it was a fuel problem, but it didn't even try. Then I pulled a plug wire and no spark. Pulled the coil wire and no spark. So of course my problem is evidently ignition related.

I did find some more burnt up wiring and think I have it reinsulated but still no spark (don't know if it is problem related or not); the white - red iginition wire was one of the ones that was burnt. I tried to check the resistance of the coil, and it does seem high; the book says .5 to .9 ohms and my digital meter was irratically reading between 1.0 and 1.3.

My manual is not very good for troubleshooting. I can see there are a lot of potential componets that may be bad such as the power stage, hall sensor, crank sensor, and possibly the computer.

I'm hoping you guys can save me a lot of grief (trail and error, replacing componets that don't need replaced, etc.)

Any help, of course, will be greatly appreciated.

Thanks!
Chuck

 

The first thing to look at next is the speed sensor.If the outside sheilding is cracked at all then replace it.That and the power stage are the 2 I would start with.They are the ones that are the most common to go bad.

 

What is the power stage?

 

he was referring to the ignition power module that switches the juice going to the coil. on a 740, its behind hte left headlight and airbox (nonturbo) or battery (turbo). on a 'regina/rex' car, its integrated into the coil.

 

so on my 850 its in the coil?

 

no idea on an 850, this is the 240/740/940 forum. there's a seperate 850 forum.

I do know, later 850s have coil-over-spark ignition where there is no distributor, instead each spark plug has its own dedicated coil/ignition power module. on a earlier 850 I'm not sure where the coil and power module are.... ok, wait. I could go look at mine, hah hah. ok, on my 96 850 turbo, the coil is on the front facing side of the left strut tower, and the power module is directly under the coil.

 

ah ok, sorry. I was just searching for help and landed on that page.

 

note that thread was 6 years old, and was talking about a completely different car..

on forums like this, its generally best you start a new issue on your own thread, so you can describe the vehicle, and the discussion in that thread can focus on one set of problems.

 

yea I did, a posted a few, but not really getting anything back on it.