1985 BMW 735 AFTER CHANGING TORGUE CONVERTER, NO FUEL TO FU

  • Tiny
  • adastra100
  • 1985 BMW 735

Engine Performance problem
1985 BMW 735 6 cyl Two Wheel Drive Automatic 220456 miles

Hi,

So after changing the torque converter, the car won't start.
It cranks, there is spark, but no fuel coming from the fuel pump.
It has: a new transfer pump, new sending unit, new fuel pump, new fuel pump relay, new main relay, new crankshaft position sensors, (both sensors at the tranny).
We tested the airflow meter, and it is okay.
When I jump the #30 and #87 terminals of the fuel pump relay, I can hear the transfer pump running, but not the fuel pump. I finally got under the car while my friend turned the key, tested the terminals at the fuel pump, and it has no voltage with the key in the ON position, but briefly while the car is actually cranking.
At this point I am thinking the thermo-time switch or the cold start valve. Also I have hear it could be the ignition switch.
Do you have any ideas. I have been working on this car for a year, and am really getting frustrated.
Any ideas would be great. Thanks in advance.

Wednesday, June 30th, 2010 AT 3:47 PM

21 Answers

  • Tiny
  • Dr. Hagerty
  • Expert
  • 9,706 posts

The wire to the + side of the fuel pump is green/violet, that same wire goes to the pre-pump, they are wired in parallel. My guess is that the wire has been compromised or the fuel pump died. Have you tried powering up the main pump with a jumper wire from the battery? Take a wire from the pre-pump and run it to the main pump and see if you get any power there. The cold start has nothing to do with the power to the pumps.

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Wednesday, June 30th, 2010 AT 4:58 PM
  • Tiny
  • adastra100
  • Member

Hi Dr Haggerty,

I thought of running a wire from the battery. I will try that this weekend. That isn't a permanent cure though.
It's probably a nightmare to replace that wire to the fuel pump, but I will try bypassing it for now anyway.

I like your cat. We have a female Russian Blue that looks exactly like that. She likes to wear plastic bags like they're evening gowns and walk majestically around the house as if she was the Queen of England.

I will let you know what happens. At this point any help is great.

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Wednesday, June 30th, 2010 AT 7:24 PM
  • Tiny
  • Dr. Hagerty
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Stick with it, we will get it going. And my cat has the distinction of having my BMW automobile repair shop named for her, Grey Cat Automotive.

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Thursday, July 1st, 2010 AT 12:10 AM
  • Tiny
  • adastra100
  • Member

So over the last two weekends, I found out that the BRAND NEW fuel pump I put in was bad. We hooked it up to the battery, and nothing. Thanks Autparts Warehouse. So I bought another fuel pump and tested it first, and it's good. So I put it in yesterday, but I still get no fuel at the fuel pressure regulator, and it only runs if I jump the fuel pump relay.

If it's running at all, shouldn't I get fuel at the regulator?
I noticed that there are at least two fuel filters. One right before the fuel pump, one right after the fuel pump, and one before the fuel pressure regulator. At least they look like fuel filters. Could they be clogged enough to stop the flow of fuel completely?

Also, if the fuel pump runs when jumping the fuel pump relay, then doesn't it have to be a problem before the relay and not after?

Do you think it could be the ignition switch?
Also, my repair book says a no start could be the thermistor switch or the cold start valve.

At this point any ideas would be great.

Thanks very much

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Monday, July 19th, 2010 AT 4:23 PM
  • Tiny
  • Dr. Hagerty
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Start with getting pressure at the filter, take it out to see if it's clogged and the other round things aren't filters, they aren't needed, take them out.

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Monday, July 19th, 2010 AT 10:23 PM
  • Tiny
  • adastra100
  • Member

Hi Dr. Haggerty,

My God it's been a bad couple of weeks.

Oh well.

Can you tell me, what are those round things if they're not filters? Are they regulators of some kind?

I will install a new fuel filter. The fuel pump still doesn't run with the key on. Do you have any ideas about that?

Thanks very much

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Tuesday, July 20th, 2010 AT 2:25 PM
  • Tiny
  • Dr. Hagerty
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They're dampers. Replace the main and fuel pump relays and see what happens.

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Wednesday, July 21st, 2010 AT 1:56 AM
  • Tiny
  • adastra100
  • Member

Hi Dr. Haggerty,

Ok, so I replaced the fuel filter this weekend.

Now, when I jump the fuel pump relay, I get lots of fuel coming from the fuel regulator.

But only if I jump the fuel pump relay. I already replaced both the fuel pump relay and main relay.

Could it be the thermo time switch? They cost $137 so I would like to have some idea. Doesn't it tell the cold start valve to open, which tells the fuel pump to run for 8 seconds?

Thanks very much.

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Monday, August 2nd, 2010 AT 7:36 PM
  • Tiny
  • Dr. Hagerty
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Early Motronic controls the fuel pump relay, if there is power to the fuel/main relays and the pump runs when you ground out the fuel pump relay, then there is a problem with one or both of the crankshaft sensors or perhaps they got crossed when the car went back together. Switch them and see if there is joy.

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Monday, August 2nd, 2010 AT 8:52 PM
  • Tiny
  • adastra100
  • Member

Hi Dr. Haggerty,

That is a good suggestion, except that I already replaced both sensors with brand new ones. Then I tried switching them, but it didn't crank at all, so I put them back, and it at least tries to turn over.

So, I am still stumped.

Thanks in advance for any help.

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Tuesday, August 3rd, 2010 AT 5:05 PM

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