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Discovery 1 - Engine stalls/turns off while driving
Hey team
New member here and rather new to the Land Rover scene. A few months back I purchased a 1994 V8 Discovery 1 that had been made as “a good one out of two”.
Since then I’ve been chasing multiple issues, but the one I haven’t been able to fix is the engine stalling/turning off whilst driving. It also has a rather high idle - around 1,050 RPM and upon starting can shoot up to as high as 3000 - 3250 RPM.
Now I’m not usually a “throw parts at it” kinda guy but almost all parts changed have been stuffed. Here’s the list of what I’ve done currently:
I have also tested fuel pressure (38 PSI) and put in a second hand TPS sensor as the one in it seemed to be giving wrong readings, but to no prevail.
I had substituted in a newer MAF sensor that had been tampered with by the previous owner, also to no prevail.
one thing I have noted is the pressure behind releasing the fuel cap, however I have my doubts about this causing my issues.
The issue is somewhat inconsistent, with it running well no issues to my work but on the way having heaps of issues. It does however start up straight away each time after stalling/turning off.
At this stage I’m a little lost. I have a couple other new parts in my tool box such as an inertia switch and coolant temp sensor, but I struggle to believe these to be my faults.
Mine is RHD, but it was just sitting in the cover under the steering wheel - the panel that drops down to get to the fuse box.I soldered wires onto the existing plug, and added my own plug for the rovergauge connection to my FTDI adapter.
A poor idle and/or TPS can sometimes cause stalling, as the engine struggles to maintain it's idle speed, it can be a bit slow to react - it's a very simple system and doesn't really have a direct feedback loop - it just guesses and hopes for the best Does the stalling tend to be when slowing down/stopping, rather than while applying power?
Do you have O2 sensors?
For your idle to be that high, there is probably air leaking in somewhere, too (assuming someone hasn't dicked with it and screwed it up really badly!). Check for vacuum leaks thoroughly. The vacuum pot on the dizzy is a common vacuum leak too, now these things are old.
Clean out the PCV system, including the "flame trap" on the RHS rocker cover, all the hoses and the TEE where it joins into the plenum (there is a small restrictor in there). Also, make sure the dipstick is sealing and the little nipple on the MAF-side rocker cover has the hose connected to the air cleaner. The PCV is a "known" leak into the intake, and if it's not right, can upset the idle. Make sure the throttle butterfly closes 100%. The throttle plate should be 100% vertical when closed and should NOT be adjusted for idle etc.Make usre the cable isn't stopping it closing 100%
Clean out the "idle bypass screw" gallery (I remove the screw entirely, and use "nulon intake cleaner", which foams up and poked a long cable tie in to work it around a bit) and set the base idle as low as you can get it to smoothly run - you should be able to get it down to 525RPM +- 25... but use rovergauge, not the tacho. It should sound REALLY slow, To set the base idle, either remove the idle valve hose and block BOTH ends, or use rovergauge to close the idle valve and quickly remove it's plug, while it's closed. Then use the bypass screw to set the idle speed. If the screw is closed and it still idles, you have either done it wrong, OR there is a vacuum leak.
I have gone through and changed most parts of the PCV system as most of it was stuffed.
As for when it stalls it is definitely more prominent at low speed when turning etc, or slowing down to stop. However in saying that the other day it stopped while cruising at 50km/h 🙃.
It doesn’t have O2 sensors connected, but I can see where they are meant to be. It does however look as though they aren’t meant to be connected or haven’t been for a long time.
Vacuum leaks are definitely something on my list. I had gone down the TPS route with my second hand one but with a high idle it’s hard to say it’s changed it.
Mentioning the operation of the butterfly valve is another thing to check.
Part of me is regretting getting a “good one out of two”…. As some of the things done are starting to make me question things…..
I’ll give some of your suggestions a go and report back.
If the fuel rail has a schrader valve, maybe check if there is fuel pressure right after it stalls. Otherwise it might be worth a look at the electrical connector at the fuel pump. My 94 does not have a schrader valve, so I bought a fuel rail from a 96 to install.
Intermittent problems are hard to find, but could be caused by a loose wiring connector. Some have reported problems with rusty connections at the fuel pump. Maybe ignition switch is loose? Really hard to find since it keeps working, way easier to find if it just broke completely.
X2 for AlW's recommendation to check throttle plate position and clean out the base idle passage. If throttle plate goes past zero (equal distance top and bottom) at idle position, that can cause stalling when the pedal is pressed since air will choke when the plate passes zero.
I see you are in NZ... mee toooo!!! Where are you?
Is yours a jap Import? Both of them? If you're running a "cat" tune, but it has no O2's it won't be happy. I think it runs rich then. You can also change tune resistors to use a non-cat map.
If it has no O2's, in rovergauge, you can see what the CO trim resistor is set to, to see if the resistor in the MAF is working. You can *mostly* see if the MAF is functional too, but there are multimeter tests that are better for small issues (startup spike voltage and stabilisation etc).
Honestly, Rovergauge is the shiz for seeing what the ECU sees... though I'm a total nerd, so I like that stuff! I have rovergauge on laptop and on my phone and keep the cable in the car, plus I can burn EEPROMs for the 14CUX.
I never had random stalling issues, but I had hot start problems (from leaking injectors) and idle issues, related to that, because it would be too rich from the leaking injectors, then the O2 feedback would cause it to lean out the mixture causing hunting.
This pic is directly under the steering wheel.
The left plug is the tune resistor plug, though I've extended mine to the white plug and resistor to the left of it.
The right plug, is the diagnostic plug that Rovergauge uses... but I've added the plug to the left of it, which I have on my Rovergauge cable.
Theoretically, yours should be in vaguely similar positions, but may be lightly taped to the loom.
I’ll have a scan tomorrow and hopefully my plug location is the same as yours. I believe mine is a UK import so there’s a chance it’s different 🙃 but once I find it I’ll take a photo for anyone that may struggle in the future.
As for the O2s, I think 2 have been chopped off and there may still be two connected, but I’ll have to verify this. I think what has happened is when the previous owners removed the cats they took the pipe off of their other one and married the two together.
As I said in my response to John I’ve got Friday off so it’ll be my testing and fault finding day. Cheers again
There are only 2 actual O2 sensors, pre cat (or where they were removed from!). The second set of sensors are temperature sensors to see if the cats are melting from being too hot - they are are rear ones, and go up into the floor, where there is a module behind the glovebox they go into.
Discovery 1 - Engine stalls/turns off while driving
Does the stalling tend to be when slowing down/stopping, rather than while applying power?
Where are you?
