stevieturbo wrote: ↑Sun Sep 07, 2025 10:50 am
The injectors have clips that secure into the rail, you can lift the entire rail out and crank with injectors all pointing into jars.
Although whether that's easier than just swapping to different cylinders and re-trying...debatable. But sometimes a visual can help.
Thanks for the help.
Thats an interesting one as I have an aftermarket trumpet base supplied and fitted by RPI. The flange of the trumpet base stops me from taking the fuel rail off. They did two things to stop me removing the trumpet base, firstly glued the trumpets themselves in place with something I cannot release. Secondly before gluing them in lets put a huge amount of torque into the securing bolts so an open ended spanner has no hope of getting them off (trumpets stop anything else from being used).
Fortunately its quite tall so there is just about enough room to get the injectors out otherwise I would have had to destroy the trumpet base. Getting them back in is going to be fun.
Its a good idea though, I could buy a second hand fuel rail and extend the wiring and fuel line be an interesting experiment.
So two new injectors fitted, engine all back together but no difference.
Not sure what the two clean exhaust ports are trying to tell me but the car wasnt running on 6 cylinders. Infra red thermometer tells me all exhausts are roughly the same temperature perhaps Odd bank running slightly cooler.
Power wise the engine seems ok, no different to what it has always been which is nothing startling a bit better than a 3.5. What I have now are very white spark plugs and on restart with a hot engine idle surges to 2000 rpm (base idle has been set). In addition although the engine runs cool at speed temperature climbs very quickly at idle.
I think I need to sort the week mixture out first. This is only a recent thing so not sure what has happened. I noticed when I had the Plenum off that the RPI supplied idle mixture control stepper motor is just a £12 ebay special so this is the first thing I can change. As I am getting good fuel pressure the only other thing that I can think of are the O2 sensors but according to RoverGauge these seem to be operating and not showing any errors.
Dissapointed I thought I had found something but all the work over the past week has been for nothing.
Maybe unplugging and replunging in your injectors cured a doggy contact for those two injectors to explain the clean exhaust ports?
White plugs obviously suggest its too lean, which can also cause high temps.
The clean exhaust ports are the reason for me changing the two injectors but this has made no difference to the engine. At idle the motor feels unsteady, not misfiring as such just not smooth. This might just be the tune level. Overall it doesnt seem to produce much power and sounds strained when accelerating.
Had a good look at the valve gear nothing seams wrong.
I measured the height of the valve springs when compressed and they are all pretty much the same so I am getting full valve movement even on the two suspect cylinders 4 and 6.
Did a leak down test and results are all pretty much the same staying within the green band on the gauge around 20% loss. Certainly no sounds of air escaping or bubbles in the coolant so I am pretty happy that I have no leaking valves, rings or gasket issues.
I have fitted the new stepper motor so need to do a base idle.
Still struggling with this, I replaced the stepper motor which seems to have sorted the idle surge issue, I also fitted new O2 sensors as a precaution.
I have a new problem now, at a steady speed on a flat road the engine is silky smooth then suddenly backfires several times then goes back to being smooth again. Never done this before.
Plugs are very white still, not sure if this is overheating or a lean mixture.
When the engine is running do those cylinders have sparking spark plugs and squirting injectors? I cannot see this in your diagnosis?
You have not wasted a week, you have spent a week identifying what ISNT the problem.
As usual it is probably something simple, and perhaps the fault only manifests dynamically (when the engine is running), so i suggest pull plugs and injectors on the two bad cylinders and visually confirm both spark and fuel on both...
Yes I can confirm that I have spark and fuel arriving at all cylinders. All plugs are identical in colour and all exhaust manifold temperatures are the same.
I did find a fault with the fuel pressure regulator in that on ignition switch off pressure dropped to 0 psi straight away. This has been replaced but the overall lean condition still persists, plugs are very white.
I replaced the fuel filter and blew some air through all the lines no sign of any blockages.
The only thing left now (that I can think of) is the MAF. This is an aftermarket Bosch unit and I am having trouble trying to physically get a good voltage reading from it to test due to its plug design.
Just as a recap, the engine has never pulled as well as it should but the lean condition only appeared two months ago. Previously plug colour was good. I have replaced - O2 sensors, two suspect injectors (but I think these where actually ok as are the rest), spark plugs, stepper motor, ECU water temperature sensor, distributor, coil (tried with and without power amplifier and either a 0.8ohm or 1.2ohm coil) and fuel filter.
In terms of testing - smoke tester shows no leaks on inlet system or on exhaust, RoverGauge shows no errors, O2 trimming is normal, stepper acts normal, fuel pressure is now 40 psi (tried 42 and 38), ignition timing is strobed at 10' (with the 123ignition distributor I have tried various base settings and curves without any effect currently gone back to old distributor). Compression test showed #4 and #6 to be weaker but within 10%, leak down test showed all ok. I am not loosing any coolant and inspection camera does not show any washed pistons. Mechanically engine does not make any nasty noises. Tick over is a little rough but steady think this is just the state of tune. Also checked that the crank pully timing marks coincide with TDC.
RPI supplied an ECU with a Tornado chip marked as being for the 4.2 engine most likely in a standard form which I feel is responsible for the poor performance, I have written to Tornado for advice but not had a response. I dont think this is responsible for the sudden lean running though.
After replacing the fuel pressure regulator I have not had the misfire in my last post but I am not confident this has been solved yet, on the previous journey it was a good 5 miles before the engine started missing.
I think as stated it is something simple. Everything I do makes no difference to performance or the lean condition which is frustrating even when I wildly alter the timing curve on the distributor. I have tried to see if the cam timing is out with the camera but cant quite make it out, I cant see RPI making this mistake though.
I am reluctant to replace yet another relatively new part but I may have go for a replacement MAF just to rule it out.
Is it perhaps something simple as a bad earth/ground connection
Perhaps try a couple of jump leads to back up existing battery to chassis and chassis to engine.
Not sure how many time things end up being a bad earth
Ian
Owner of an "On the Road" GT40 Replica by DAX powered by 3.9Hotwre Efi, worked over by DJ Motors. EFi Working but still does some kangaroo at low revs (Damn the speed limits) In to paint shop 18/03/08.
I currently have two earth leads to the engine block at the front, one goes directly to a bolt sharing the battery earth on the chassis and another on the other side of the engine goes to the coil mounting on the inner wing and to the chassis.
Looking around on the net I see references to earth straps on the back of the cylinder heads? I think at least one of them was for radio interference. I dont recall having these on the original engine. I think it is worth my while making a couple up wont do any harm.
Yep checked fuel pressure, assuming gauge is accurate its currently at 40 psi. I only have the standard narrowband O2 sensors fitted is there a piece of kit that you can read wideband sensors with? One thing I havent done yet is to create a logfile using RoverGauge.
Its a 14CUX/Hotwire system, other than a remote CO trimmer there is no adjustment on the MAF
Last edited by heli_madken on Sun Sep 28, 2025 4:11 pm, edited 1 time in total.
