No Fuel Pump priming on B34 engine

Rek

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My car cranks for a while then starts - it can take 4-5 seconds.

On the donor car, the engine started instantly, every time. I understand that the ECU operates the fuel pumps for 1-2 seconds once the ignition is turned on which makes starting more instant by building up pressure, then the pumps are constantly on once the crank position sensor is sending the signal that the engine is running.

So, having followed all the instructions, and everything else working well, why would my fuel pumps not prime on ignition on any more? Once running, all is well, but the cranking cannot be good news and this is foxing me.

I have a number of connectors running into the ECU box (or where it was) but I think that these are related to something else. They are:

Connector 1 with two brown wires. (Earth?)
Connector 2 has brown/blue + green/violet wires going in - (O2 sensor? My car did not have one)
Connector 3 has red + green/black + white/black + blue/black
Connector 4 has brown + green/white + green/brown

ABS might be involved and perhaps some gearbox controllers, but I cannot isolate the connectors from the wiring diagram.

Has anyone else had this issue, and if so, is there an easy solution?
 

sfdon

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Check valve shot?

Do the right thing- use a fuel pressure gauge and report fuel pressure readings before and during cranking.
 

Rek

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Yes - thats what I thought too, but its a new valve, and an upgraded fuel pump (Bosch 044) which seems to work well. The pressure is nil before cranking, when it should be something. I think once cranked, the pressure builds quickly and the engine runs with no issues.

It wasn't always like that - i used Por 15 in the tank but forgot to unblock the fuel return. I am using a swirl tank so the back pressure built up when not using fuel quickly (in town) and it would stall and not start until the pressure equalised. I replaced the pump and the valve after that just in case. Could that have affected something?

Its not a big issue but it would be nice to have it start instantly like it did on the donor car.
 

sfdon

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FPR is dumping pressure?
Visegrip fuel return line and monitor pressure
Then feed line
Then cold start line.
 
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Rek

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I tried that - pressure is fine, but I added a non return valve ahead of the pump for good measure. I think this is an electrical issue. The pump should prime but doesn't. Either something is wired wrongly, or it might be the relay. It might be something or some connection in the donor car which I don't have, like something in the dashboard cluster or ignition switch.

For those with a B34 transplant, can you let me know how your engine starts. Does it need to crank or does it start instantly?
 

Tony.dreamer

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As Don said , Use a fuel pressure guage and see how quickly your pressure drops after you shut off the engine . I am guessing you might have restricted the return/ vent when you POR your tank....perhaps messing up the proportion of return or something .
You might also leave the gas tank cap off the car and see if it make a difference...
 

sfdon

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Jetronic or motronic?
Which Ecu?
Do you hear the pump run with key switched on?

Jetronic has the fuel pump switch in the afm.
It also has a wire at the starter.
When the car is cranking or the afm door is open the fuel pump operates.

Early Motronic pump operates for a second and then operates when the ecu sees teeth moving on the flywheel. Missing teeth, bad fuel relay or bad bellhousing sensor will cause problems. Notorious issue is bad connector at either sensor cable.

Later motronic gets crank signal from front of engine. Known problem is crank sensor too far away from toothed wheel.

You should do the obvious- probe from volt meter into back of pin 87 of your fuel relay. Do you get voltage when key is switched on? Voltage when cranking?
 

Rek

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Thanks for the responses. Motronic 1989. No - the pumps don't prime with the key on. Thats the issue. New relay ordered. I will test the 87 connector for voltage and keep digging.
 

sfdon

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Pin 3 at your ecu sends a ground signal to the pump relay at pin 85 - brown/green wire to activate relay.
Test for ground at pin 85 when turning key on with relay out.
 
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