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1986 740 turbo crank no start issue

ZVOLV said:
Schrader valves weren't on these cars until 1992.
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My bad - guess he'll have to open the line some place else then - same as if he did have a gauge

Actually safer that way (shade treein' it) he can point a hose into a can to do the basic visual check for pressure

As you have already correctly pointed out though, it's a ground problem anyway
 
Repaired the harness, put it back in. Everything works the same. Checked for fuel at the injector by pulling the rail, regrounding grounds, and plugging in one injector plug at a time and cranking: Nothing.
Checked for fuel at the rail and now I'm getting absolutely nothing, so went to the next source and checked my fuse, fuse was fine. Checked the fuel pump relay and the main pump is audibly functioning.
So now what? Air lock in the system? There is fuel in the main tank, probably about 40% full, is an airlock possible? Thanks.
 
Not airlock.

Put the car on stands in the rear. Shake car, make sure it won't fall. Crawl underneath and disconnect the line coming from the tank. Put a pan underneath attempt to start car.

My guess is, you get nothing.

Let us know.
 
The pan is to catch fuel in case the in-tank pump *is* working.

My guess is that it *is not*.

I could be wrong. Try to be careful.
 
swedefiend said:
The pan is to catch fuel in case the in-tank pump *is* working.

My guess is that it *is not*.

I could be wrong. Try to be careful.
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But even if the in tank fuel pump is not working, the main in line fuel pump should bring some fuel to the fuel rail right? Or not.
 
dfk said:
But even if the in tank fuel pump is not working, the main in line fuel pump should bring some fuel to the fuel rail right? Or not.
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No.

Sometimes it can. When the pump is new and the sock is clean.

Original / old main pump, original / old tank sock...

All bets are off
 
Vapor lock is kind of like air lock. But, not in the sense that it can be bled out. The only way to fix it is to replace the in-tank pump (or move the main pump into the tank - which is what they did to late model 740s and all 940s IIRC)
 
Fuel - fire - compression

You KNOW you have two of them because the engine will run when you give it something to burn
So first, determine is you have INJECTOR PULSE
If you don't have a plug in noid light you can do it with a test light
Clip the test light to the positive battery cable and prob the control side of the injector harness (the side of the plug that's not 12V+ when the key is on) (unplugged from the injector) while a helper cranks the engine over - the light will blink dimly if you have pulse

If no blink, you've found your problem and need to track down why, open circuit, faulty relay what have you - if it DOES blink then you have a fuel DELIVERY problem - fuel pump(s), relay etc

A no start is not that difficult to pin down - just relax, think about what you're looking for and use logic
 
Not getting any fuel at the rail whatsoever, new pumps (both are working) and filter, relay is working confirmed by audibly hearing both pumps run for a short time after bumping the starter, main pump is receiving 10.5v while cranking, tank is roughly 65% full of clean gas. Tried blowing out the lines with compressed air, at a total loss here. Is 10.5v not sufficient enough?
 
Pull the fuel return hose and jump the pumps and see if anything comes out.

Could have a clogged fuel filter, clogged tank pump sock, torn tank pump hose.

Something doesn't add up here....you could also pull the hose from the tank pump off at the main pump, apply 12v to the tank pump and see if anything comes out and then work forward from there, IF it's really the problem. Some cars even have a Schrader valve on the hose from the tank to the main pump. Either way it's easy to check. I would use a spare battery, a power by one, a jumper pack, a helper to crank, long wires, etc. It's easy to make pumps go and see if anything comes out
 
ZVOLV said:
Pull the fuel return hose and jump the pumps and see if anything comes out.

Could have a clogged fuel filter, clogged tank pump sock, torn tank pump hose.

Something doesn't add up here....you could also pull the hose from the tank pump off at the main pump, apply 12v to the tank pump and see if anything comes out and then work forward from there, IF it's really the problem. Some cars even have a Schrader valve on the hose from the tank to the main pump. Either way it's easy to check. I would use a spare battery, a power by one, a jumper pack, a helper to crank, long wires, etc. It's easy to make pumps go and see if anything comes out
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I re&re'd my intank pump today to triple check electrical connections, grounds and in tank pump filter. Blown compressed air through the feed line from in tank pump to main pump, and from filter to fuel rail. Pulled the filter off and as far as I can tell isn't clogged. If hypothetically somehow the in tank pump filter got clogged and was not letting any fuel through, would that also mean that the main pump would not be able to pull any fuel through? Also could I run compressed air down into the in tank pump to try to force back the clog, I'm afraid I risk blowing off the in tank pump. Furthermore, is 10.5 volts at the main pump sufficient/standard during cranking?
 
Yes it is.

What happened when you added power to each pump to verify flow?

________


I mentioned several ways to jump the pumps and I can think of a few more. If I suspected no fuel flow I would go with whatever is fastest. In this case fast would be one hose clamp to pull the fuel return line and then a helper to crank the engine. Or even just pinch the return line, no pulling it off, and have a buddy crank and see if it swells under the pressure. It wouldn't tell you the amount of pressure or volume but give you at least a dead or alive reading. A gauge would be ideal. You can rent one from O'Reilly for free and it goes on the outlet of the fuel filter. Or get a 1992 plus fuel rail and a 90 degree fitting. Or at the shop, if lucky, we would have a master fuel pressure kit that might have the correct fittings.

The fact that you have replacement fuel pumps is a red flag. Maybe a failure or something went wrong with the recent repair.
 
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I respectfully disagree ZVOLV. This kind of voltage drop is usually a sign of a bad relay.

FWIW, I already suggested checking transfer to main flow testing. I don't think we ever got results of that...
 
ZVOLV said:
What would acceptable cranking voltage be at the fuel pump?
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Anything over eleven.

The voltage drop at the pump is really only supposed to be 0.5V per the green books IIRC.

edit:// I don't have access to green books anymore. Feel free to correct me if I am wrong.
 
Ok well if he jumped the fuel pumps with a nice hot 12v the car would start if the relay were the issue.

I still argue that 10.5v while cranking is normal. Voltage drops that low even at the battery while cranking.

My 1990 240 would pop start and run, barely, with a dead alt and only 8v or 9v at the battery.

A voltage drop test, the different kind, could be done at the relay to check for bad contacts.
 
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