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Old 08-05-2017, 10:43 PM   #26
dfk
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Originally Posted by swedefiend View Post
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.
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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Old 08-05-2017, 10:48 PM   #27
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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.
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
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Old 08-05-2017, 10:51 PM   #28
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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)
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Old 08-05-2017, 11:01 PM   #29
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The only way to fix it is to replace the in-tank pump
QFT

The rest of my reply was hypothetical. Not actually a reasonable suggestion to get your car running.
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Old 08-06-2017, 11:25 PM   #30
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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
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Old 08-08-2017, 07:30 PM   #31
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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?
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Old 08-08-2017, 07:50 PM   #32
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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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Old 08-08-2017, 08:36 PM   #33
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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
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?
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Old 08-09-2017, 03:13 AM   #34
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Furthermore, is 10.5 volts at the main pump sufficient/standard during cranking?
No.
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Old 08-09-2017, 09:14 AM   #35
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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.

Last edited by ZVOLV; 08-09-2017 at 11:50 AM..
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Old 08-09-2017, 01:03 PM   #36
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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...
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Old 08-09-2017, 01:43 PM   #37
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Well, could also be a weak battery...
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Old 08-09-2017, 02:25 PM   #38
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What would acceptable cranking voltage be at the fuel pump?
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Old 08-09-2017, 02:32 PM   #39
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What would acceptable cranking voltage be at the fuel pump?
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.
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Old 08-09-2017, 03:09 PM   #40
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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.

Last edited by ZVOLV; 08-09-2017 at 05:11 PM..
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Old 08-09-2017, 06:26 PM   #41
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Fuel is now making it to the rail, injectors are getting power but the car won't stay running. Insufficient fuel pressure?
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Old 08-09-2017, 06:54 PM   #42
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Get a gauge on there and check. How would WE know?

Do an idle test and a snap throttle test.

What do you mean fuel is "making it to the rail"?

There is fuel pressure and also volume. Maybe one of your new pumps has gone bad.

Maybe retry the fuel injector spray into a bottle thing again.
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Old 08-09-2017, 07:06 PM   #43
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1986 740, B230FT LH 2.2 Crank no start issue.

Car cranks over with no sputtering or attempts to start up at all. Car will start and run if fluid is sprayed in TB until you stop spraying.
There is no fuel.

Quote:
Originally Posted by ZVOLV View Post
Since it runs on fluid it's likely a fuel issue.
---

Now, there is a pump in the tank and a main pump under the car. Both are controlled by the Fuel Pump Relay.

What is the voltage at the main pump *before* attempting to start.
What is the voltage at the main pump *while* attempting to start.

What is the voltage at the in-tank pump *before* attempting to start.
What is the voltage at the in-tank pump *while* attempting to start.

Have you disconnected the fuel line going *into* the main pump (coming from the back of the car) and verified that there is a lot of fuel coming out of the tank while attempting to crank the car (would likely overfill a 16oz bottle while cranking for three or four seconds)?

Quote:
Originally Posted by ZVOLV View Post
What do you mean fuel is "making it to the rail"?
I would also like to know...

Does breaking the connector at the rail (male/female 14mm connections IIRC) cause there to be enough fuel that it is literally sprayed from the connector when you break it?
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Old 08-09-2017, 07:18 PM   #44
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Just so you know...

The only way you would have a fuel pressure problem that would present a no-start condition and NOT have a dead pump is for the fuel to be dumping all over the ground...

AFAIK, even a bad fuel pressure regulator would allow the car to crank and idle (albeit roughly...) But, this is the reason why ZVOLV has been trying to get you to pull the return line.

Last edited by swedefiend; 08-09-2017 at 07:30 PM..
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Old 08-09-2017, 08:18 PM   #45
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Okay, got the car to fire up by unplugging the maf, started idling at around 1300rpm, stayed there as it reached operating temperature. The car wasn't responsive to rapid throttle actions like if you tried to blip the throttle it wouldn't accellerate, if you gave a slow steady increase in throttle it will rev up but drops to about 800 rpm upon throttle release. Shut the car off and it wouldn't start back up again, I suspect a faulty CTS. Would that cause my other issues as well?
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Old 08-09-2017, 08:28 PM   #46
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Okay, got the car to fire up by unplugging the maf, started idling at around 1300rpm, stayed there as it reached operating temperature. The car wasn't responsive to rapid throttle actions like if you tried to blip the throttle it wouldn't accellerate, if you gave a slow steady increase in throttle it will rev up but drops to about 800 rpm upon throttle release. Shut the car off and it wouldn't start back up again, I suspect a faulty CTS. Would that cause my other issues as well?
All these issues were with maf plugged in, tried starting the car with maf unplugged and plugged in made no difference
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Old 08-09-2017, 09:24 PM   #47
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Sounds like intermittent electrical. Not enough info here to diag. Good luck.
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Old 08-09-2017, 09:51 PM   #48
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Sounds like intermittent electrical. Not enough info here to diag. Good luck.
Darn shame, thanks for all the help you've given thus far.

Anyone else care to diagnose? Pressure is verified at the rail and I'm getting
spark
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Old 08-09-2017, 11:03 PM   #49
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Current symptoms are as follow:

Car will not stay running while MAF is plugged in if you crank for approx. 6-8 seconds with the throttle fully open it will sputter to life for about 4 seconds and then slowly die back down.
Car will start with the MAF unplugged if you crank for approx. 6-8 seconds with the throttle fully open it will slowly increase rpm's enough and idle in a limp mode of sorts. From here, the car can be manipulated to idle by manually holding the throttle at 20% for 15-20 seconds. After some time, the MAF can be plugged in and the car will idle quite smoothly at 1300-1400 RPM, but acts quite bizarre. If you try to smoothly engage the throttle it will increase in RPM without hitch, however, if you try to 'blip' (going from fully closed to about 60-75% open quite quickly) the throttle, the car will not respond and if you attempt to 'blip' it repeatedly it will start to stall out.

Things I've confirmed

Spark is present
Firing order is correct
Repaired engine bay wiring harness
Cam is in time with crank
FPR is not ruptured, though you can smell the very faint smell of gas at the vacuum line although the line is clear of gas
Both pumps are running

Thanks again for trying to diagnose over the computer, I understand this is very difficult to do.
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Old 08-10-2017, 11:59 PM   #50
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Bump
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