Freaky 3.5EFI runs without ECU ???

[Taz]

Hoping you can help..

Whilst trying to fault-find a mates 88 rangie that refuses to start, we in-advertently started her up whilst the ECU was disconnected, and it runs and idles fine !!! It didn’t like throttle but it idled quite smoothly. We just let it idle away for at least 5mins and stop and started it a few times and it started fine and ran smooth ???

We had disconnected the ECU plug to check the water coolant sensor, the thermotimer, the extra air value and the injector resistances, all of which were fine. We also checked the fuel pressure via a guage in the cold start injector hose and that is also OK.

We thought it may have been a failed cold start injector so we isolated that but it made no difference.

Prior to this, we checked the compression which was excessive >> 200psi. So we took some plugs out and kicked her over only to see a torrent of fuel being thrown out. I also had a spare ECU which runs fine in my RR however that made no difference, although it did run OK for a few minutes before it seem to flood itself and die. From that point on it wouldn’t start again - back to square one.

Whilst we had the engine running with the ECU disconnected, we removed the leads from the even bank of cylinders (all 4) and it still ran as before. However if we removed the odd bank it wouldn’t start.

After about 30mins of test without the ECU, the engine no longer idled. It would start and run for about 1-2sec and then die. It did this many times - each time running briefly then dying. At this point it didn’t matter which bank of plug leads we removed - as long as one bank was connected it would run briefly. We then reconnected the ECU and it ran brilliantly - for about 5mins when it started flooding itself again. From that point the run would run and idle with the ECU once more.

We checked to see if the injector pins on the ECU plug were shorted, but they were all open circuit with the ignition on.

It seems like something is pulsing or holding the injectors open (ie earthing) independently from the ECU. Weird.

The oil level has also risen slightly and the oil is now thin and smells of fuel. I guess this is just fuel dribbling thru the ring gaps.

Any help greatly appreciated!

[BigJon]

The ECU only controls fueling, not spark, so with an extra fuel supply which you clearly have i am not surprised it ran.

[Taz]

Just had a thought...
Could it be the diaphram in the fuel pressure regulator?
Perhaps if it's perfurated, fuel can be sucked thru the vacuum pickup and into the throttle body just behind the butterfly?
Then again fuel pressure was measured at around 37psi, so perhaps it's OK.

[PLR]

G`day Taz

your pressure test was by opening the flap to get pressure , not running ?

At idle it could have 26 other wise it can suck in extra fuel .

The time it ran would probably be related to the amount of fuel in the rail .

The power resistors perform in banks , there may be an electrical fault with them , though the norm would be to not work not overwork .

The fuel pressure reg would be my thought and maybe some injectors that dribble .

If you take the vac pipe off the reg and there is fuel to be found , it`s not working as it should ( lowering the pressure ) and probably the problem .

From what you`ve typed i presume that you have a manual .

Cheers

[Blknight.aus]

when was the last time the injectors were cleaned up.

if they are dribbling then they will leak fuel at any time the fuel rail has pressure.

[Taz]

Thanks gents,
Some additional info...
Seems it runs on either bank. When leads to both banks are connected it runs at around 1400rpm, when leads to either bank are removed it runs at closer to 700. So perhaps all the injectors are dribbling and making a contribution. My mate was going to test the pressure regular this morning. If it's not that then I guess it must be dribble. Although I have problems getting my head around dribbling injectors being enough to run the engine without the ECU and enough to prevent starting with it.

Oh and thanks PLR - yes we did test the pressure by opening the flapper (not running)

Thanks again,
Taz.

[BigJon]

Where are you ? I have the complete injection system off my 3.5 Rangie in the shed. It was all working very well when I removed it (upgraded to 3.9 engine and EFI).

[Taz]

John, thats extremely generous of you, however unfortunately I'm in Perth.

[BigJon]

Bit far to try parts substitution!

[Taz]

Well - It's always something simple...
When checking out the fuel regulator my mate discovered the vacuum hose was disconnected !!! So the regulator would have thought the throttle was wide open all the time, therefore increasing the fuel pressure to max. That together with worn/weeping injectors could explain the dribbling and running without ECU. The extra air from the disconnected hose would have allowed more air in behind the butterfly also. It seems to be running fine now. We are going to change the oil and take it for spin to be sure.

BigJon - if I may change the subject a little... Seems I'm following in your foot steps... I'm also preparing to replace my 3.5EFI with 3.9. I have obtained a second hand hotwire ECU, AFM, loom, injectors etc off a 3.9EFI, but I was actually thinking of keeping the 3.5 flapper EFI as I know it works. That, and it looks like it will take some time to work thru both wiring diagrams so I splice in the new system to the existing fuel pump ect. BigJon did you find it a big job? Would you do it again?

Thanks in adv,
Taz.

[BigJon]

From memory there were only about 6 wires to connect!

I found a few good websites with wiring information.

Have a look here. Rover 14CUX Hot Wire Mass Flow EFI: Service and Troubleshooting (http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm) down the bottom is a guide to wiring pins on the ECU. As far as other wires I just spliced appropriate colours under the dash for oil pressure, water temp and battery light. The temp guage isn't quite accurate (reads high) and it is on my to do list.

I wouldn't hesitate to do it again. My original plan was to keep all the 3.5 stuff including timing cover and ancilliaries, but I am glad I didn't.

The actual wiring to get it to run took about 2 or 3 hours.

[Taz]

BigJon,
That a huge help!
Many thanks.

[BigJon]

No worries, if you have a search I have a few threads from when I did the conversion too. Got a few pics in there as well. Feel free to ask any questions.