Hey all,

So I'm just about to bite the bullet and scrap my newly acquired 1987 740 turbo. I am however giving it one last gasp before I do this, as I have invested 3 weeks of time being stuck in Boise, USA on my travels from NZ.

It all started when I broke down on the interstate 8 miles out of Boise. The oil pressure dropped and the power dropped, before the car stalled. I managed to get it to a gas station where I topped up the oil, before attempting to get another 7 miles to my friends place. I got within a mile and it died, properly! Would not restart. I managed to get it to a nice mechanics and we have been tearing our hair out since!

We have managed to rule out that the car is lacking oil pressure, and have also tested fuel relays, pumps and fuel pressure which all appear to be fine. It was cranking to a start initially for a second or so before stopping initially, and now it won't even get that far!

The entire main wire harness crossing through the engine was entirely rotted out and had patch jobs, so with high optimism I pulled the thing out and spliced in a section of one that I acquired from the local pick-a-part. It did not start I thought I may have done something wrong so I checked continuity between all wires between jetronic and ignition control systems which appear to be fine. I have also had the good luck of having an electrical engineer look at it who says after checking my work suggests that it is probably something else at this stage.

I have gone through all the manuals and checked through the forums for a solution to no avail. I have checked powerstage, coil, relays etc and still having no luck.

A possible direction?
I checked the voltage through the spark wires today and found that sparks 1 and 2 are only receiving about 3 kV, whereas 3-4 are getting between 12-15 (much more healthy). I pulled out the hall sensor and saw that there was a decent amount of oil contamination. I attempted to clean this up and re-put it back in, only for the engine to crank even less effectively than before. I think it may be worth trying to find a scrap total replacement for this and putting it in and seeing what happens, as well as replacing the spark plugs which have now fouled out.

Any ideas? ANY would be greatly appreciated. I can only give this a couple more days before I have to make the hard decision and scrap the poor thing. My email address is phil.clunies.ross (at) gmail.com.

Thanks so much,


Phil

 

I am not so sure the wiring is perfectly sorted out, it may give you all kinds of issues.
The Hall Sensor wire, did you check that? Did you replace the hall sensor? I imagine you have eliminated FUEL as the culprit and are concentrating on SPARK. Are the engine GROUNDS OK, the ones attaching to the intake especially?

 

Thanks for your response! I have checked the voltage running through the hall sensor wire and they match the values that should be reaching them. I went to pick-a-part this morning and got a hall-sensor which was in fantastic condition for $9. The distributor cap has continuity from the teeth to the plugs, however the inside has a dry yellow residue inside and does not look like it is in the best shape. I attempted to clean but it is being very stubborn. Unfortunately the cap that was with the hall sensor was no good.


How could I go about checking the grounds? I have noticed that the battery has been losing charge rather quickly.

 

Well, look up the grounds, then make sure they are clean and tight. Particularly the two on the intake manifold and the straps on the valve cover.

 

there's only one coil, all 4 plugs get their spark from the same place, directed by the distributor. if your distributor cap is shot, thats a replacement item (along with the rotor).

but you got a pile of other issues there, the wiring sounds really sketchy. 86-87 seem to be the worst years for the 'biodegradable' wiring harnesses.

 

This a way good walk-through on just that car:

Home

Look for the page "Diagnosing No-Starts on Some 740/940 Volvos"

I'm thinking the hall effect sensor as well.