Fuel pump cutting out

[Yatz]

My Chimaera 4.5 has developed a curious problem. The fuel pump suddenly switches off, or at least that's what it seems to be doing. I can be driving along and suddenly the engine just dies. If I press the fob on the key just as you would when first starting, the pump comes back on no problem so it's working ok, it just likes to turn itself off for no reason. It seems to do this when the engine is hot as the problem generally happens as I am returning home from a drive. Is this a common problem?

[Steve_D]

There are many and varied reasons for the fuel pump stopping assuming that is in fact what is happening.

When you first switch the ignition on the ECU earths the fuel pump relay which in turn powers the pump. (fuel pump prime).
The pump/relay then goes off until the ECU sees a spark signal from the coil indicating the engine is cranking or running.

I'm suspecting this may be loss of the spark signal as this is produced by the ignition amplifier which are famed for hot failures.

Next time this happens watch carefully to see if the tacho drops rapidly indicating it has lost signal.

You could also set up a couple of test lights on the fuel pump relay.

• TL1 between pin 87 (2 wires White/Purple & black) and earth.
This will light when the relay is powering the pump.

• TL2 between pin 85 (Blue/Purple) & Pin 86 (White/green).
This will light when the ECU is telling the pump to run.

At Ignition on both should light then go out. At start they should both come on and stay on.

At engine fail if TL1 & TL2 stay on then the pump or its wiring are at fault.

If TL1 goes out but TL2 stays on, then the relay has failed.

If both go out and the engine is still turning then the fault is somewhere before the fuel pump relay.

There is a lot of talk about old relays but the original metal bodied relays are Bosch and very well made. I would trust them more than modern replacements.


Steve

[Yatz]

Thanks for the feedback. At the moment the problem seems only to occur when the engine is hot, when I have been driving for an hour or so. I can start the car and go for a short drive and everything is fine. When it cuts out all I have to do is press the fob as you do when turning off the immobiliser and the engine starts again so it's basically the immobiliser coming on which is, of course, the fuel pump turning off.

[Steve_D]

I can supply an (reversible) immobiliser bypass instruction you could try out to confirm the immobiliser is the issue.
PM me.

Steve

[Muffin8372]

After some advice, replace the fuel pump/ ecu relays. At one point I had a similar issue, which is now resolved due to Dom @ powers offering his vast advice. Got to be worth a try as they are cheap too!!

Good luck

[Yatz]

Having looked more closely at this issue, I notice that when the engine cuts out the rev count drops immediately to zero. My thought would be that this indicates that it might be the ignition relay rather than the fuel pump relay. (although turning the fuel pump back on is all that is needed to restart if the car is moving) Does this make sense or would the fuel pump or ECU relay failing still cause the tachometer to drop to zero? My current thinking is that I should change all the relays but I am still curious as to what is happening.

[Belle427]

Usually a sign of an ignition problem on the coil primary or switched side.
Check the wiring to the coil and ignition module first as the connections do suffer a bit here.

[dogbucket]

There are two inline Lucas resistors on spade terminals taped into the engine loom near the coil. One is in series with the feed from the coil to the rev counter and one in series with the feed to the ECU to tell it that the engine is running. On my car the one in the ECU feed was breaking down in the heat so the ECU cuts the fuel pump when it lost the signal. When measured with a meter the resistor was open circuit. On my car it would not restart for a while once the problem started. I soldered a 1/4W resistor (I forget the value) across the failed Lucas one and that resolved it.

Had a few embarrassing MOTs with it cutting out and not restarting. Also a 450

Edited by dogbucket on Saturday 6th July 15:44

[Steve_D]

A few comments on earlier posts.
• There is no relay in the ignition supply side.
• The rev counter dropping is a very good sign of ignition issues.
• I’ve only ever seen one resistor in the ignition path that being on the line to the ECU (6.8K Ohm)

Another possible source for this problem is the ignition amplifier which is known for failure evident as it gets hot.

Steve

[SMB]

I had exactly this issue, car would die suddenly but immediately restart, well it did until it wouldn’t but that took an annoyingly long time. Everything tested ok when stationary but would fail 300 miles later or 10. In the end replacement of the alarm/immobiliser solved it.

[Belle427]

I had 2 resistors on my 95 car, as explained by a previous poster above.

[lancepar]

I'd try running the pump backwards first for a bit, just reverse the connections, won't do any damage. It may have a blockage.