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Range Rover classic 3.5efi flapper won’t fire injectors


clivebrown
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Hi I have a rrc 3.5efi, I bought it as a none runner that had been on carbs but the bloke had reinstalled the efi system. I found the resistor pack was missing and bought that (treated it with ohm meter all is fine). Changed the coil, tried a different MAF. The engine turns over and fires fine when fuel is sprayed in to plenum chamber. Fuel pump works. I have power to injectors, but they don’t fire, I have jumpered out the fuel over run relay and the resistor is inline. I have continuity tested the b/w wire to pin1 on the ecu and it reads fine.........but the injector don’t fire, Ive tried a noid light...nothing...I guess I’m not getting the pulsed earth to trigger....is this an ECU issue? I have another ecu and have tried that but got the same results. Is there anything else effecting the pulse on pin1?

Help is gratefully received...enjoying the process...but its getting a bit wearing now!! Ive been up and down all the forums...

 

Clive

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The ECU will only fire the injectors if;

1. There are pulses coming from the coil -ve on the WHITE/BLACK wire into the ECU (via the over-run relay, WHITE/BLUE)

2. The airflow meter flap is slightly open (there's a switch in there)

There's a full flapper EFI diagnostics manual in the technical archive, work through it step-by-step, don't skip steps because you "know" something is OK!

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Indefinitely have continuity, and spark, the engine fires with fuel sprayed in and tries with fuel from the cold start...just not firing injectors. Oscilloscope (cheap one) turned up today, I’ll see if that can pick the pulse and dwell time....

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I'm trying to remember the usual faults with these... the red relay (item 12) might benefit from a continuity check, diodes inside as pictured - also check there's 12v when cranking as I believe the purpose of that little cluster of bodgery is to keep the fuel pump & injectors powered whilst cranking (white/red wire from starter solenoid).

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There's a relay mounted near the ignition coil that was a regular problem, can't remember if it cut the ignition or fuel... I vaguely recollect it was used to cut the fuel or ignition when the engine wasn't running or on overrun (no signal from the flapper ?).

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Yep, there's a little vacuum switch teed into the fuel pressure regulator's vac line that switches the over-run relay and kills the ignition pulse to the ECU - white/blue wire one side, white/black the other, you can safely jumper it out of the system permanently.

You can tell it was another afterthought because it's not on the wiring diagrams :lol:

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I’ve jumpered out the over run relay so there is a feed there, I’ve ensured there is a 12v ignition feed at cranking, red white wire. I’ve tried a handheld oscilloscope on the pin 1 today, it appears to be a regular signal......run out of ideas...I was trying avoid buy a recon Ecu, like I said I had two but you never know if they are both broken...the plektron relay has current coming out both side to power fuel pump. Fuel pump runs with flap open (hear it). I think next is to remove plenum and get an injector out, try and manually pulse one. 
 

im not convinced there wasn’t an alarm / immobiliser before, someone has cut one out I think and it looks likes they put the wires back together....current have the dash in bits chasing wires....

 

any other ideas gratefully received...this bugger won’t beat me!!

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As we're grasping at straws a little bit here, something else to throw in the mix that's an easy check...

How confident are you that the injectors aren't opening ? Just wondering if you might have a fuel issue rather than electrical as such. Bear in mind that the last time i player with flapper systems was probably over 20 years ago and I hated the system so much I changed them all over to hotwire or MS at the earliest opportunity !

I have a feeling that on a working flapper system, with ignition turned on, you should hear the injectors click when you floor the throttle. If the fuel regulator is stuffed, not delivering enough pressure to the fuel rail, that would give the same symptoms as injectors not opening and one of the common failures of that regulator was for it to drop fuel pressure, essentially just returning the fuel directly to the tank.

With that in mind, the fuel pump is running obviously but have you checked you have fuel at the rail ? I once spent 2 days chasing a similar fault only to find the walls of the fuel line had collapsed with age and were blocking the fuel so the pump was fine but almost no fuel at the regulator.

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I very much doubt it's the ECU, and there's a lot of simpler/cheaper stuff to check before throwing money at another one!

Have you downloaded the flapper EFI troubleshooting guide that's in the technical archive section and worked through  it? If not, you really really should - do every single step, don't skip anything, and tell us how far you get.

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14 hours ago, clivebrown said:

Yeah I downloaded various troubleshooting guides, I have fuel at the cold start. I think I need to get rail off and at least one injector out. I don’t hear the injectors click....

You said you'd tested with a noid light, so do you have power and pulses at the injectors or not?

Hearing them click is a bit marginal as a test.

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There is pulse to pin1 ecu from -coil checked with handheld oscilloscope. But the noid light shows the that the injector isn’t pulsing. I was wonder if the injector circuit is as simple as coil pulse to pin1, power to resistor pack to injectors. Or whether there is another requirement at the ecu for the injector pulse to create the earth??

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You should have 12v from the resistor pack on one side of the injector and then the ECU grounds the other side to fire it. There's at least one or two large ground wires coming out of the EFI loom that need to be bolted to something, and obviously the ECU needs a 12v supply too.

I don't know if the flapper does this but some ECU's will not fire the injectors if the throttle is wide-open (position sensor reading max) during cranking as a "flood clear" mode, and those throttle position sensor wires fall off for a living.

But, you know, diagnostic manual, step-by-step, etc. etc...

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  • 1 year later...

If it starts with cold start injector and starter spray you may have a bad ignition switch. If the wire that goes to EFI relay is sitting on a burned spot when key is on run or start position the injectors will not pulse. I had vehicle that ran perfectly if I used starter fluid or would start first thing in the morning with cold start injector. Other wise it would just crank with no start. After many days of chasing ghosts and analyzing schematics I traced problem to burned spot inside ignition switch.

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