Relay Location 740?

There's only one fuel pump relay, it's the one in the console.

I feel like a broken record sometimes, but if you haven't replaced the engine wiring harness, do that first. 90% of the intermittant engine problems I see in these cars are from rotting insulation in that harness, up until '89 or so they simply *all* rot, and any still running on original harnesses are running on borrowed time before they have weird unpredictable problems or leave you stranded. When I cut mine open, it was a big bundle of bare copper wires in a cracking outer sheath full of insulation dust. I rebuilt it on the street by soldering new wires to the original connectors using heatshrink tubing to replace the original sheath.

Does the tach twitch when you crank the engine? The ECU will not power up the fuel pump unless it detects ignition pulses.

That's what I thought.

Tach does twitch.

Has spark (I believe but not 100% verified).

Cannot hear pump noise.

When it dies, it's like someone threw a switch.

thanks

jimB

Can you measure voltage at the pump? Did you replace or resolder the relay already? Fuses ok?

When mine suffered the harness failure it would randomly start running poorly and have no power, then recover. Then one day the engine just shut off and would not restart. When I cut open the harness to replace the wires, I was shocked it had run at all, the insulation literally crumbled to dust from a large bundle of fuel and ignition system wires a couple feet long.

Look at the date stamp on the relay...if it's close to the manufacture date of the car replace the relay...it's all of $50 for good quality/ OE and $30 for Chinese. It is not worth the hassle to resolder the joints, etc. unless you a truly a geek.

Best regards

wharf rat

volvos since 1969 PV544, 122 Amazon, 145, multiple 240's, 940 and, currently, 87 245 and 93 850.

In a time long ago and a galaxy far away, jimB did his own car repairs. No longer. Well, some repairs anyway...

With the help of a Bosch ignition guru , problem was determined to be Hall Effect Sensor in the distributor. Power module was also bad but I don't know how that figured in the cause/effect equation.

I have a parts car (doesn't everyone?) and I pulled the computer, distributor and power module.

All betta

Second benefit, speedo works now (intermittant before). Go figure. Did pull/replace grounds at computer bracket.

Had it been the harness, car would be in the scrap yard by now.

Not that it's terribly relevent, but, I do still have a 1987 harness from the parts car. Is that one the type that doesn't rot?

jimB

-------------------------------------------- JimB

-------------------------------------------- my SPAM defense: Replace all the X's in email address with M

No, that one rots too, but for about 30 bucks in parts and a couple hours of labor and you can rebuild it like new with new wires, or you can buy a nice used harness from Dave Barton for a couple hundred bucks. Installing it on the car takes about an hour. You'd seriously scrap the car rather than do that?

Well, I suppose if it only takes an hour, that WOULD be silly. Who knew.

I will keep it in mind.

I would have to go with a new or reliable used harness. Me and soldering irons don't get along.

I am actually a professional designer. I have designed and built harnesses from scratch but never tried to splice into one.

I had someone splice a harness (from a u-pick) for me on a car that had had a fire. Didn't work too well.

It ended up adding a lot of failure points.

If this is such a problem, maybe I should build a harness board and sell harnesses .

jimB

It wouldn't hurt, up until around '89 they all fail, it was an experiment in biodegradeable insulation, however engine heat and oil caused it to degrade much more quickly. Given more time and a source of new connectors, I'd have built a whole new harness myself. Brand new ones are obscenely expensive.

When I did my '87 I had little choice, the car died and I needed transportation so I bought a few rolls of wire and a big pile of heatshrink tubing. Removed the harness from the engine but left it poking through the firewall and proceeded to replace each wire from near the firewall to right at the connectors. The copper was oxidized in some places but I was able to scrape it clean and solder a new wire on then slip a piece of heatshrink tubing over it. The job took about 4 hours and I had to do it on the street because I couldn't get the car up my steep driveway, it was miserably cold and raining out, but the finished product looks factory and the car has been dependable ever since.

I also built a custom harness when I put Megasquirt on my 242, that one I took my time, salvaged connectors from the scrapyard and built the whole thing from scratch. Took longer but it also looks factory original and has been dependable.