Kar1179 (relative to your post 4-8-22, which I'm just reading again); I believe you are correct in that the ECU requires an engine RPM input signal see below (it's Pin # 39) - I've read it should be ~7v. I have that signal, but still have the issue. I believe you are correct in that there is an 'initial squirt' that's not occurring. BUT my Defender shows that this actually occurs prior to cranking, when the key is still in the engine-run position. I measure a consistent 'initial squirt' from the Defender of between 1400ms & 1700ms of duration (quite long!), when I turn the key to the engine run position (and you hear the pump prime) prior to cranking. Then when I crank the Defender, it fires right up. My Discovery's 'initial squirt' is more like 40ms to 60ms - I feel this is the problem too. But just to reiterate (and add for other readers), I have a crank RPM signal, my Coolant & Fuel temp sensors resistances measure perfectly in spec. when measured at the ECU pins and are exactly the same measurements when taken directly at the sensors them selves (so the wiring is good) AND this issue is not specific to engine cold or engine hot - it can occur (and it does ~95% of starts) at any engine temp.

 

JohnZo (Relative your post yesterday); I'm sure you're right, but I feel like all I've found out it is; what it is Not, and still don't know; what it Is! Also, I'm out of time (according to my wife). fyi: I have changed the coil (with an original OEM Lucas part), also the ignition amplifier when I was going through the ignition system (and throwing parts at the truck - which I'm happy to do). I believe the ignition to be good - I have an inline spark tester connected to one of the spark plugs showing that I always have spark when cranking. I have adequate Fuel pressure at prime (~38psi), fuel pressure regulators appears to function correctly. Note: Truck fires right up with Starter fluid sprayed into the intake plenum (via the brake booster port), then does Not without it, then Does with it. I've done A-B-A testing to prove this to myself. I believe it to be an initial fueling issue where for whatever reason the fuel injectors are not getting a command (signal) to inject fuel as they should and is required to start quickly.

 

Question for Kar1179: Could you provide a little more detail on how you wired your toggle? I think my specific questions are:
1) I presume you spiced into the two 'ground side' wires for the fuel injection system (one for each bank), Yellow/ White (RH bank, goes to Pin 11) and Yellow/Blue (LH Bank, goes to Pin 13)
2) What did you use for your ground? A convenient point on the body, one of the 'grounds' at the ECU or did you run a ground wire back to the Battery neg?
3) Did your toggle switch break the connection of these two wires to the ECU while switched (for a second or two) or not? I'm not sure if this matters, I'm just a bit concerned about the ECU seeing a ground directly back to the battery when it's not meant to! As started before I think, electrical systems are not really my thing).
Any help much appreciated - I think I'm headed down this root too as my solution!

 

Have you checked or replaced the TPS? They can wear right at the closed throttle (starting) position, since that is where they spend a lot of time, and the TPS will impact initial starting conditions, and checking with an ohmmeter can be tricky (and intermittent).

Base idle is another potential culprit. Mine was low (below 500 rpm, tested with the IACV blocked off) and started better after adjustment (3/4 turn CCW) to increase air. That passage also needs to be good and clean. Maybe a bit more air will give you a bit more fuel to start. Setting the base idle is described in the Workshop Manual. As is the base timing adjustment (which I assume you have already checked). You'll need to drill and pop off a metal cap to access the base idle screw.

The MAF sensor also has a CO trim adjustment that affects fueling at starting and idle conditions. Mine seemed to take longer to start when the voltage was adjusted lower. It is factory set, and usually only needs adjusting if the MAF has been replaced. I followed a very detailed and helpful write up by RPI Engineering to set the TPS voltage and the MAF CO trim voltage. CO trim adjustment is also under a metal cap.

Hope this helps.

 

JohnZo; Thank you for your comments.
1) I did my best to 'check' the TPS a while ago with the use of a multimeter - it behaved like a potentiometer and I didn't find any 'dead spots' around closed throttle position. However, I will swap with the Defender TPS to rule this component out, as it's a relatively easy to do.
2) I've read about the 'Base idle' setting and it's always been in the back of my mind! The 'idle' sometimes hunts or wonders high then low then high then low - I've replaced the IACV in the past, but the idle still 'sometimes' can be a little erratic like I've explained. I will attempt to set the Base idle as described in the RAVE, although I'll have to trust the Tachometer for engine speed, nothing more fancy.
3) If by 'base timing adjustment' you mean ignition timing? Yes; I've checked this - spot on at 6deg BTDC.
4) I believe my MAF sensor is original (I've not changed it in 17yrs and the truck's run perfectly during this time). I have recently swapped the MAF sensor with the one from the Defender - it made not difference, so I swapped it back. I'll find and read up the RPI Engineering article you've referred to, but will 'park' this adjustment for the timing being and investigate the TPS and 'Base Idle' first. I'll try and do it this morning and report back.

Thxs, Ian

 

Relative my post yesterday (4/18/22):
1) Not quite so easy to swap the TPS between the '94 Defender and the '95 Disco - they have different connector's (this must be why I didn't do it before!), the Disco has a rectangular connector and the Defender a round connector. I've ordered a 'used' one from the internet.
2) My assessment of my 'Base idle' was that it is about spot on - just over 500rpm (as indicated by the instrument panel Tachometer!), the idle was a little bit lumpy. I back out the adjustment screw 1/4 turn (CCW), the idle 'felt' much smoother, but the indicated idle speed was now ~650rpm (Spec. is 525rpm +/-25rpm), I left it there to see if it made any difference to starting - it did not.

When ordering the TPS, I also ordered a replacement ECU. I intend to keep this truck for ever and certain components will become more difficult to source so I figured a replacement TPS and ECU can't hurt to have for the future. I will try both these components in the future when I receive them (probably next week) and see if they make a difference - keep you all posted - if this continued part swapping doesn't fix it - I'll pull the trigger on the Kar1179 toggle switch band aid - for what I use my Disco for - that will be perfect!

 

Apologies on the slow reply, I was out of town. It was a couple years ago now so I don't recall exactly what I did - but I do remember some of what I didn't do... I didn't run the ground back to the battery, and I didn't isolate it from the ECU (I just grounded the circuit). I don't recall if I grounded it to the chassis or if I used another ECU wire. I also used a fresh coil, but it wasn't an OEM one, I believe it was a MSD coil.
I went through the manual and verified all checks specified there, and all were fine. I recall a resistance reading for the resistor in the coil to ECU wire, but I don't recall a voltage (may be there and have checked, I just don't remember). So when I have a chance, hopefully this weekend, I'll check that. I can trace back by toggle wire as well and let you know where I ran it to.

 

A few words about base idle. Remember it is set such that the IACV will be able to control normal idle under various load conditions. So, the IACV will operate at a different stroke position if we change the base idle. The IACV may have a bit of difficulty controlling idle if base idle is set too high or low. For example, if base idle is set at normal idle speed of 665 to 735 rpm, then the IACV will need to be fully closed to try to control, and that could impact controllability when load changes (e.g. A/C compressor kicks in).

I think it is normal for base idle to be a little lumpy at 500 rpm. Even a few rpm lower and it may not start or keep running. Any way, you might want to think again about where you leave it set.

The truck looks great up in the mountains, by the way!

 

ok - thxs Kar1179 I've also been out of town, but I plan to get back to it this weekend and wire in 'the toggle switch'!. I've checked out my TSP, base idle control setting, MAF sensor setting and plugged in a replacement ECU!! Everything checked out fine and the new ECU made absolutely no difference at all!!
I'm planning to simply 'spice' into the Bank A & B injector ground wires just before they enter the ECU at pins 11 & 13, connect them to a toggle switch which will be grounded to the body close by the switch. I may just wire up Bank A first and see if this is sufficient to aid a quicker start! Let me know if this makes sense or if you have any comments or suggestions. Lastly, do you activate the toggle switch during cranking? Or only prior to cranking? How many seconds do you activate the toggle switch for ? Many thxs, Ian