Rover 3.9 14CUX Hotwire - Fires Up but Won’t Run

[GDCobra]

Around 8:45 to 9:00 minutes in

Ian

Didn't realise Alan Partridge did EFi!

That wire he's talking about is the feed to the coil, although it may come out in the same area as the AFM bundle it is not related, this is the ignition trigger, and should go through a 6K8resistor. Without this the engine won't run at all.

[Ian Anderson]

As I said about 20 years ago!
I was fairly sure it was black……but mind played tricks.

When that wire came disconnected my car would start but not run.

Ian

[Steve R]

Definitely a whiff of Partridge about that video!

Good to see it all laid out though. Thanks for sharing, really useful. Yep, can see now that it’s the signal wire from coil to ecu and it does come out close to the MAF connector. All connected on mine.

Having done some more research I do suspect my fuel pressure could be low. Previous owner had installed a single external pump setup - I replaced the pump for a new one (so in my head had ruled this out), but sounds like it’s a big ask for one pump to lift fuel out of the tank and supply it at Efi pressures. Will test it properly at the weekend, but I feel a swirl pot and 2 pump setup might be next…

[GDCobra]

As I said about 20 years ago!
I was fairly sure it was black……but mind played tricks.

When that wire came disconnected my car would start but not run.

Ian

That's surprising, with no pulse from the coil there is nothing to trigger an injection cycle (calculation and injector trigger) so should not run at all.
Only thing I can imagine is there was some fuel in the plenum or intake manifold (leaky injector maybe) so the engine would fire but then stop when all available fuel fumes burnt, a bit like starting a car with an alternate fuel source as a test for fuel or spark issues on crank no start.

[Steve R]

This weekend’s update…

Found two interesting things, so adding it here in case it helps others.

Firstly I did a smoke test on the intake system. My cheapo solution was to do as follows:
1. Remove plenum intake pipe and maf.
2. Cable tie the throttle butterfly open.
3. Find a suitable plug for the plenum intake hole (I used a snug fitting aerosol cap).
4. Take a tealight and remove the wax bit (I wanted the foil tray).
5. Pop in a smoke pellet (sold cheaply for testing chimneys).
6. Light the pellet in the foil tray, pop just into the plenum inlet and plug the intake - it’s a 30 second burn time.
7. Look for smoke escaping!

This revealed a couple of leaks which could be causing my problems. I had removed the ‘hot spot’ plate on the bottom of the plenum as I didn’t need it. Turns out only two of the bolt holes for this are not blind - they go right through into the intake, letting air enter. Typical that I originally only checked the two blind holes!

So, a couple of bolts later and we’re all airtight.

However, I also found another problem - very low fuel pressure! Investigating further a rusty fuel tank has killed my new pump I think. So it’s new tank and pump and filters before I can test for success…

[GDCobra]

This weekend’s update…

Found two interesting things, so adding it here in case it helps others.

Firstly I did a smoke test on the intake system. My cheapo solution was to do as follows:
1. Remove plenum intake pipe and maf.
2. Cable tie the throttle butterfly open.
3. Find a suitable plug for the plenum intake hole (I used a snug fitting aerosol cap).
4. Take a tealight and remove the wax bit (I wanted the foil tray).
5. Pop in a smoke pellet (sold cheaply for testing chimneys).
6. Light the pellet in the foil tray, pop just into the plenum inlet and plug the intake - it’s a 30 second burn time.
7. Look for smoke escaping!

This revealed a couple of leaks which could be causing my problems. I had removed the ‘hot spot’ plate on the bottom of the plenum as I didn’t need it. Turns out only two of the bolt holes for this are not blind - they go right through into the intake, letting air enter. Typical that I originally only checked the two blind holes!

So, a couple of bolts later and we’re all airtight.

However, I also found another problem - very low fuel pressure! Investigating further a rusty fuel tank has killed my new pump I think. So it’s new tank and pump and filters before I can test for success…

Thanks for the update Steve. I've also been looking into doing a smoke test on mine to check for leaks and you're mention of these smoke pellets the other day gave me an idea. I've possibly gone a bit over the top with my method, I made up a smoke canister the other day which I intend to put the smoke pellet in (your tea light foil tray is a good idea too). My intention is to pipe this into the 10mm dia inlet for my servo line which will fill the inlet tract with smoke and hopefully expel it all out of the MAF which I'm intending to leave connected but remove the air filter.

Your not about the bolt holes on the heater plate has got me thinking, can't remember if I removed this or not as I don't need it and it's not piped up, I'll check this tomorrow.


I did suspect low fuel pressure from your description of the issue, I think I mentioned this a few posts back. It's an easy thing to overlook. Frequently it gets checked with engine off but many people don't realise that as soon as fuel starts getting used the limited flow can't sustain the pressure (a bit like testing a battery with no load on), it can be difficult to test with engine running as rail pressure varies with manifold pressure anything up to 14PSI difference from WoT to overrun, but you should be able to see if it's way too low.
I guess running the limp map with extended injector open time just allows the engine to run?

[Steve R]

Your smoke cannister sounds like a great idea! My method worked but it wasn’t very elegant!!

Yes it’s the two bolt holes nearest to the engine on the ‘hot spot’ plate which go right through into the plenum inlet. Worth a check as it wasn’t obvious.

Re fuel pressure, yes I think you’re right - limp map was opening the injectors just enough to allow the engine to run, which confused me into thinking it was electrical. Was waiting on my pressure test kit - glad it finally arrived.

Thanks for all the pointers, hugely appreciated.

Just need to get a new tank and pump installed and we’ll see if it runs!!