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1985 BMW 735 After changing Torgue Converter, no fuel to fu

Tiny
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  • 1985 BMW 735
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 220,456 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.
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Wednesday, June 30th, 2010 AT 3:47 PM

21 Replies

Tiny
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
Tiny
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OK, so lets start fresh, the car will crank, but not start, you replaced the torque converter. You installed new sensors. You have spark but no fuel. You replaced the filter and now there is fuel, it still will not start. What else is there that I am missing? Have you tried spraying fuel or brake cleaner in the intake to see if it will light off?
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Tuesday, August 3rd, 2010 AT 11:53 PM
Tiny
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Hi Dr. Haggerty,

Well, it's been a couple of weeks. I get fuel at the fuel pressure regulator. Both crankshaft sensors are new and in the right position.

I tested the thermo time switch and found that there is no power at the brown and yellow wire with the key turned on or off.

There should be power after turning on the key for 8 seconds or so.

When I test just the switch, it gets about 1/3 the resistance it should have.

Do you know why that could be?

Any ideas would be so great.

Thanks!
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Friday, September 10th, 2010 AT 4:19 PM
Tiny
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Is the car running yet, or are we still chasing the cold start issue?
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Saturday, September 11th, 2010 AT 3:53 AM
Tiny
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Hi Dr. Haggerty,

The car still won't start. I'm still stumped.

Aaack!

Thanks for any ideas.
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Monday, September 13th, 2010 AT 1:15 PM
Tiny
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OK, let me review the data and I'll see what I can see.
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Monday, September 13th, 2010 AT 6:20 PM
Tiny
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Some clarity of the facts please. Which repair manual are you using? You stated the engine has spark and no fuel, you fixed the fuel issue, there is spark and it still does not run, even if you spray fuel into the throttle body, is this correct? Is it cranking over?
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Tuesday, September 14th, 2010 AT 8:03 AM
Tiny
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Hi Dr. Haggerty,

Yes, it is cranking. There is fuel, but only if I jump the new fuel pump relay.

I am using a Haynes manual that covers the 1985 535i, and the mechanics manual for the 1984 733i.

Those are the closest manuals I can find.

I also have the E23 electrical troubleshooting and wiring manual in PDF form.
It shows where all the components are, and the wiring for the car. I just am not very good at reading it.

The one thing I do know is there is no voltage at the thermo time switch, which activates the cold start valve.

Thanks for helping, it's keeping me sane.
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Tuesday, September 14th, 2010 AT 3:38 PM
Tiny
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Forget the cold start, it has nothing to do with the car not starting. Focus on the injection of fuel at the injector, use a Noid light or a 5 watt side marker bulb to see if there is an injector signal. Spark and fuel and the thing will start, what the heck is the deal here.
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Wednesday, September 15th, 2010 AT 8:44 AM
Tiny
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Hi Dr. Haggerty,

I could try that, but I don't know what you mean.
Could you explain that further?

Thanks.
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Wednesday, September 15th, 2010 AT 6:41 PM
Tiny
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OK, check the ring gear for the top dead center tab, they often break off. Its a little tab welded to the ring gear, roll it over by hand while you look through the lower access hole. If it broke off, it aint gonna run.
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Thursday, September 16th, 2010 AT 10:59 PM

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