Started, quit, and the mystery began...

Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
Well, the crank position sensor is replaced with a new part from AB. After all the terrible stories I read online, it was far more straightforward than I anticipated. It was FILTHY in that little corner of the engine, and I spent more time scraping out gunk than I did replacing the actual part! My spacer was all one piece. Swapped it from the old sensor to the new, and bolted it back up, plugged it back in and replaced the cover. Naturally, it’s been raining, and I got to lie in a puddle while doing it, but so it goes.

Reconnect the battery, hook up the multifunction relay, and go for a start attempt. No dice. Engine cranks away, but the pump still won’t turn on.

By now it was raining in earnest, and I was pretty dejected. I’ll head back out this afternoon or tomorrow and start my diagnostics over again. Something is preventing the fuel pump relay from activating. I just have to figure out what.
 

best4x4

Well-known member
Mar 1, 2015
595
72
Beaumont, TX
You have to make 100% sure the wiring to the CPS is in good condition. I've seen em with just bare copper and no insulation or twisted and shorted out.
 
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Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
You have to make 100% sure the wiring to the CPS is in good condition. I've seen em with just bare copper and no insulation or twisted and shorted out.

Now there is something I hadn’t thought of. Okay, I’ll see if I can get a multimeter on those wires tomorrow...
 

Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
I spent a chunk of yesterday and this morning under the Disco pulling the plug on the Crank Position Sensor to test continuity on the wire harness from the CKS to the ECM. As is becoming almost routine, there was good continuity all the way. We’ve been doing a lot of learning over the holiday about the GEMS system and the Land Rover installation. I, or my wife, have read just about every LR document the internet will dredge up, as well as some other brands guides. (Morgan has some good info on GEMS, by the way.) Turns out, the way the ECM commands the pump relay is by opening and closing the earth path for the control side of the relay. Fuel pressure modulation is done with the injectors, fuel pressure regulator, and the fuel tank return. All that is to say, once the pump is signaled on by the ECM, it remains on at constant speed until the ignition is switched off. If we can’t solve this, I’m developing a new scheme to run the wire that would typically carry the ECM earth path directly to ground instead, thus cutting the ECM out of the loop on turning the pump on and off, but maintaining the simplicity of the ignition switch as the fuel pump switch, and the safety of the inertia switch in case of collision. However... the wife, being a professional business intelligence developer/data analyst, isn’t quite ready to write the ECM off. So we’re in the market for a few new ideas as to what would cause the ECM to not want to power the pump. Based on the documentation, the only inputs without a default strategy built into GEMS is the CKP and the MAF, and a MAF failure shouldn’t shut down the fuel until 550 rpm, when the ECM checks it for signal. (I suppose that is the argument for not running the FPR relay straight to ground... the ECM couldn’t cut off fuel if it stopped being able to measure air...) All of which is to say, I’m running out of ideas as to what else I’m looking for. We’re going to do a re-test of the volts and continuity through the whole system. I’m not optimistic about finding anything new, but one never knows what you’ll find until you check. Back to work!
 
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robertf

Well-known member
Jan 22, 2006
4,781
358
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Does the check engine light do a bulb test when switching the key from off to position 2?
 

Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
Does the check engine light do a bulb test when switching the key from off to position 2?
Yes, it does! We have suspected the immobilizer a few times in this process, but all indications are that we are not immobilized... although at this point I’m pretty sure I won’t be surprised by anything...
 

robertf

Well-known member
Jan 22, 2006
4,781
358
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Good. Have you checked for spark when trying to start? That will clear up the crank sensor input working or not. These engines diesel on starting fluid so using that only eliminates compression and valve timing
 

robertf

Well-known member
Jan 22, 2006
4,781
358
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After you verify spark...
Check the underhood fuel pump fuse for 12v on one side. Then check for continuity from the other side of the fuse all the way back to the fuel pump during the few seconds of priming. Probably need a helper and some extra wire for this one
 
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Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
After you verify spark...
Check the underhood fuel pump fuse for 12v on one side. Then check for continuity from the other side of the fuse all the way back to the fuel pump during the few seconds of priming. Probably need a helper and some extra wire for this one
Solid thoughts, Robert - and much appreciated! We will be re-checking the run all the way to the fuel pump, but we have already verified 12V at the supply side of the FPR (on the ‘98 with AEL, that’s housed in the Multi-function Relay between the washer reservoir and the evap canister) as well as verifying continuity from the exit side of the relay, going through the inertia switch, all the way to the pump. (You’re right! I needed about 15’ of wire and a helper!) We’ve also verified voltage coming from the ignition switch to the control circuit on the FPR through the white/green wire at plug C1030.

I am at work for the next week or so, so it’ll be some time before we can put any new tests into effect. But we aren’t giving up on this one... we have adventuring to do!
 

Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
Alrighty, folks. Sitrep: the Disco started*, ran, and drove around the parking lot under its own power tonight.

Now to deal with the *...

To briefly recap, after the truck failed to start on the second morning we owned it, my wife and I have been backwards and forwards through the thing trying to bring it back to life. It would crank, had spark, but no fuel pressure. In the process of diagnosis we have:
- Replaced the fuel pump
- Tested every inch of the fuel pump wiring harness for continuity and resistance, twice.
- Replaced the inertia switch
- Bench-tested both inertia switches... the old one was good
- Replaced the Multi-Function Relay (which in AEL trucks houses the Fuel Pump Relay)
- Bench tested the old MFR... it was good, and in fact, the truck started tonight ON the old MFR... (Figured if it blew up, I wanted a nicer spare. HA!)
- Replaced the Crank Position Sensor
- Verified continuity from the CKP to the ECM
- Cleaned and dressed all the grounds that address the fuel system and ECU
- Verified that the ECU is not immobilized

Nothing worked. Every time we thought we had solved the problem, we were met with the same results - cranking, but no starting. The single exception was when we ran a jumper from the battery directly to the fuel pump, at which point the truck started instantly. Since that time, we have combed every shred of the RAVE, as well as any piece of documentation we could find about the GEMS ECM and how the system works. In the process I've discovered that the ECM commands the fuel pump "on," by opening a ground path for the control circuit of the fuel pump relay, thus allowing the relay to close and energize the system. Prior to doing this, the ECM checks for a signal from the CKP, then powers the pump briefly at position II, prior to switching the pump on permanently once the engine is cranked, referencing the CKP and the MAF for continued operation.

Based on this information, and armed with the knowledge that we have a brand new CKP and functioning circuitry, I am lead to conclude that somehow, the ECM has faulted, and is not opening the earth path to actuate the fuel pump relay. Whether that is a hardware fault (there is corrosion on the ECM case) or something else, I do not know yet. However, in order to test the theory, as well as the rest of the system once-and-for-all, this evening I wired the earth side of the FPR circuit directly to ground. The FPR is now directly controlled by the ignition switch. It is permanently grounded, and receives power continuously from the time Position II is selected, until the ignition is switched off. Lo, and behold, the engine fired up immediately, and settled down to idle at approximately 950rpm. After allowing it to warm up (there was a fair bit of cold-engine noise) we cautiously put it in drive and took it for a loop around the lot (I didn't want to find myself having to push it back home!!!) without issue. We never got out of first gear, but the truck runs and drives, with no hesitation or stumble on gas application or modulation. The engine shut down smartly when switched off back in our parking spot.

So. Here I sit, a whiskey in hand, with a truck that starts, runs, and drives, and yet still no solid answers. Assuming that the ECM does in fact have a hardware problem, I now need to wade into the sticky issue of how to source a replacement ECM or have mine fixed. This seems to be a bit of a contentious point here in Land Rover Land. What I've been able to glean is that yes, ECMs can be replaced, but that they need to be re-programmed to accept the body computer, or jail-broken to run without its input. Is that correct? Are there any GEMS ECM gurus here who can guide me?
 
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Frobisher

Well-known member
Dec 27, 2012
200
68
Pennsylvania
As someone once told me, get comfortable with mystery.

It’s good to hear you have forward progress. If you stay within a small radius of your place, you could get towed back on the cheap if it came to that. Hopefully, it won’t!
 
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rover rob

Well-known member
Mar 29, 2016
273
56
upstate NY
I've got like 4 GEMS ECU's for my non AEL 97 D1 and I can swap em out whenever I want with zero issues.
having 4 d1s I have 3 spares plus I have the program Robert f wrote in my phone so I can reset the adaptives and resync the ecm to the alarm ecm.
 

best4x4

Well-known member
Mar 1, 2015
595
72
Beaumont, TX
Not all the same P/N, but they are all non AEL ECU's. I use the older Britpart Lynx for resetting the adaptive settings, however it's 10AS resync section is a joke and does NOT work.
 

Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
I appreciate the feedback re: swapping ECMs. I'll begin the hunt for an AEL ECM to see. I'd love to get a Hawkeye/Lynx/similar, but they're a little rich for my blood at the moment, and the availability seems challenging. (Looks like the new Lynx isn't even sold in the US?) In the meantime, I'm going to put the truck back together and start driving it a bit - hopefully I can build some confidence in it's reliability!
 

rover rob

Well-known member
Mar 29, 2016
273
56
upstate NY
look in the search for resetting adaptives. you will find the info for the program Robert f wrote and you can reset the ecm yourself for cheap.
 
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Spark6

Well-known member
Oct 31, 2020
127
40
New Hampshire
Look up Will Tillery in NC (willtillery@roverguy.com) or Paul Grant in CT (classicroverparts@gmail.com). They part out LR's and I have bought a bunch of stuff from both.

Will do! Good steer, I appreciate it!

And Rover Rob, thank you - that might be exactly what I'm looking for! I'm an iOS guy, but a cheap Android phone and a Scantool is still cheaper than a stand-alone tool like Hawkeye or iLand!
 

robbyb20

Well-known member
Oct 2, 2019
227
34
Seattle
Will do! Good steer, I appreciate it!

And Rover Rob, thank you - that might be exactly what I'm looking for! I'm an iOS guy, but a cheap Android phone and a Scantool is still cheaper than a stand-alone tool like Hawkeye or iLand!
While youre at it with the android device, i bought the table below. it has a true GPS unit in it and if you plan on going anywhere remote, you can download the maps to and have it work without needing cell towers for A-GPS devices (most phones/tablets on the market).


I also have used this device to reset my adaptive values with the app mentioned above.
 
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