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Discussion Starter · #1 ·
Hi all,

Long story short... fuse #7 is blowing upon attempting start, narrowed it down to one of the blue wires out of the relay going to the control pressure regulator -> fuse does not blow with the control pressure regulator unplugged, but of course the car won't start either! :0

Figuring I had nailed it down to the control pressure regulator, I sent it away for a rebuild (not necessarily cheap, but hard to come by part which is common to deloreans of the time)... incredibly anticlimactic when I got it all back together for a repeat performance (fuse #7, blue wire, etc. exact same problem)!

Does anyone have any experience or advice on this one? I'm feeling a bit out of my depth at this point... not sure what/how to test next. Is there any way to bypass the control pressure regulator just to test that the vehicle starts? I'm thinking this would illustrate the control pressure regulator is still the only suspect.

Any and all input is appreciated.

Thanks
 

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Did you recently replace the CPR or the wiring harness?

On some early 80s models there were two possible CPR configurations. Try swapping the wires with a couple test leads. I mean, switch the two wires that go to the CPR so they go to the opposite pins on the CPR. That should fix the problem.

I believe Dave Barton makes a note of this somewhere on his wiring harnesses page.
 

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Discussion Starter · #3 ·
Yeah, unfortunately I already paid up for a replacement (along with my original being the core swap) and put it in place... was expecting it to work. I'll try the swap, but to note it was the same behavior with the original CPR. I'm also assuming if the wires were crossed/shorted along the harness the problem would still occur when the connector wasn't plugged into the CPR..? (which isn't the case)

I'll report back.

Where would I find Dave's wring harness page?
 

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So when did the problem start? My previous recommendation only holds if you had just replaced your wiring harness or CPR.

If the car has never had the wiring harness replaced, that could be the issue for sure.

Also what else is on Fuse number 7? If the main fuel pump is on there you could have a bad fuel pump relay, which is a very common failure point.

It's WWW.davebarton.com specifically http://www.davebarton.com/volvoharnesses.html
 

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Discussion Starter · #5 ·
Ok, just went to do the wire swap test. Was getting dark so didn't quite get there yet, but... it's now clear the wiring/harness had been butchered in the past!!! It had been wrapped well so I assumed it was factory fine - inside however, one of the wire casings was deteriorating, not pretty!

History, I acquired the car, not running (and has not run under my management as of yet), thought it was fuel-pump-related but tracked it down to the blue wire coming out of the relay (fuel pump relay) fed by fuse #7 (main pump). Other, yellow wires from the relay (and fuse #7 in kind) feed the tank and main pumps. Basically, cut them one by one until I discovered the particular blue wire which, when not connected would save the fuse from blowing. It feeds the CPR and AAV. Small step further, with blue wire re-attached just after the relay, simply disconnecting the plug into the CPR also avoids the blown fuse.

All that to say, I have both just replaced the CPR (it's mine or another rebuilt as mine was taken as core swap) and the harness has either been replaced or butchered. In light of this, what would your recommendation be? We're talking about swapping the power (blue) to the ground to get them aligned to the proper port, right? Sorry if I'm asking a redundant question, just worried I might fry the CPR or something else if I don't understand...
 

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You would only need to swap the two CPR wires if you had replaced your engine wiring harness wih a different one or if you swapped your CPR with a different type.

If the car was running, then started blowing fuse 7 without any changes to the wiring or cpr or whatever else, then it's something on fuse 7 and probably NOT a polarity issue with the CPR.

If the blowing fuse stops when you disconnect the CPR and you've replaced the CPR the next step would be to find out where each of the two CPR wires goes. Then unplug the wires at their destinations and run new test wires from the CPR to the destinations. If the car works after that, then you have a wiring fault. If it still blows fuse 7 then you have a fault elsewhere, likely in the fuel relay of related.

Also if you have deteriorating wire casings, as all 1980-87 volvos do (read the first part of Dave's wire harness page) then your engine wiring harness has not yet been replaced. Until you replace it you will have electrical gremlins. Read more also here: http://www.k-jet.org/articles/projects/wiring-harness-guide/
 

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Discussion Starter · #7 ·
Reversed polarity it was, thanks so much fivealive! The car is not starting yet, but I ran the resistance tests mentioned on Dave's page and based on the results went ahead and reversed things -> no more blown fuse #7...

Now it seems I'm not getting fuel up from the main pump, either the pump itself or the fuel pump relay I'm assuming. I did run a test on the in-tank pump to ensure it is delivering but do not receive any fuel forward of the fuel filter. If you have any advice on next steps or little snafus which might be responsible (as with the CPR polarity reversal), please do share.

PS. I will be ordering a replacement engine wiring harness based on the info you pointed me to, I definitely have some deteriorating wire casings here and there (hidden by black electric tape).
 
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