Hi
I have a Pre He V12 5.3 with d type fuel injection fitted in my cobra kitcar
The exhaust has been changed to a two into one collector then a 3 inch straight through side exhausts each side of the car, the air intake filters have been changed to a large free flow pancake type filters
The fuel pressure is set at the moment to 30psi,
I have not driven the car on the road yet but it revs and idles fine
After speaking to another owner of a v12 cobra at a kitcar show recently, He said he could never get the fuel injection to work properly because of the exhaust modification and ended up fitting carburetors.
the only problem I can see is there is no adjustment on the ECU to make the engine run richer or leaner at full throttle
Can the mixture be altered just by altering the pressure regulators?
I do not want the engine to run to lean so how do I make any adjustments, and do I need a dual air fuel ratio meter one for each side exhaust?or can I just look at the color of the spark plugs.
Thanks for any help
Peter
HI Peter. I don’t have any experience with the V12 but I would think that 30 psi may be on the low side? The AJ6 engine runs between 38-40 psi and I had mine set up with an adjustable FPR set to 48psi. The rationale for my higher pressure was due to one of our members building up an XJ40 for racing. His brother used to be involved with BMW racing in the late 90’s
When they Dyno’d the AJ6 engine they ran a base HP check and then raised the FP by about 7psi and the next run up showed an increase in power. Theory being that the higher pressure produced a finer atomisation of the fuel leading to more complete burning of the charge. The other thing that I changed on my '40 was to remove ALL the cats from the system. I had the opportunity to have the emissions tested (not required in NZ currently) and even with 200K on the clock it would have passed if the tested limits were to be introduced. I know the '40 ECU has a +/- 20% on the injector duration so the feed back from the O2 sensor would adjust the injector cycle to stop over fuelling. Hope this helps in some way.
Regards Robin
If it’s a pre HE fuel injected motor, it uses a lucas version of Bosch D-Jetronic which runs at 30PSI by default. It’s common practice to increase fuel pressure to about 35-38psi in order to improve running issues and the fuel pressure regulator should be adjustable using the nut on the top.
For more info, google Bosch D-Jetronic for more info, you should find a billion links full of technical info.
a quick thought, why not change to a standalone EFI managment system?
that way all the injection parameters would be adjustable from idle to mid range to max output, using an AFR gage monitor!
and Pre he are hard to hurt for short runs , also make sure your ignition system is up to snuff.
Maybe not the best fix, you could remove the air temperature sensor lead and place a 1 K resistor across the air temperature connector. Or just leave it disconnected. It should run slightly richer. I have recently installed O2 bungs, on my 78, for testing after modifying my exhaust.
Chandler
78 XJ12L, 83 XJS MS-1 EFI
Hi Peter
I have a '80 10:1 XJS pre-HE which I have modified by running fueling and distributorless ignition with a Megasquirt-2 ECU.
I also built a Cobra with an HE engine - also managed by Megasquirt-2.
Finally, I converted a 73 E-type OTS I had to EFI again using a Megasquirt-2.
It is from this perspective that I respond to your posting. Firstly, I find it very hard to accept that any exhaust setup could result in lean fuelling at full throttle - if everything on the EFI setup was working as it should. On the std EFI setup, there are just a few things to check:
- having the correct coolant temp sensor,
- having the correct air intake temp sensor,
- the correct fuel pressure IN THE FUEL RAIL (this depends on correct fuel pump pressure, and correct operation of both fuel pressure regulators, and both having correct vacuum connections);
- having manifold pressure (vacuum) correctly connected to the ECU.
- finally, the “full load enrichment switch” should activate when manifold pressure approaches barometric pressure (basically when maximum torque is demanded). Note that at low revs, as little as 30% throttle could result in near barometric pressures in the manifold.
- if Lambda sensors were fitted, they need to be present an fully operational
Adjusting fuel pressure might fix fueling for one operational condition (eg full throttle) but may cause problems in another area (eg light throttle or idle). Fuel pressure (IN THE FUEL RAIL) should thus be correct as per the EFI system being used.
I’ll also mention that the “horse track” injectors with double the flow rate of the later rectangular HE injectors and this on its own creates challenges, more so at idle and light throttle conditions.
A wideband AFR gauge would certainly tell you within minutes if the fuelling of an engine is on target or not. (I would recommend the Innovate Motorsports MTX-L - its what I use). A very basic guideline is that you should have 12.5 - 13.5 at idle, very light throttle, and at large throttle openings, and between 14 - 15 at partial throttle.
There is no need to have two Lambda sensors. You can monitor both banks one at a time. Fueling should be the same on the two banks assuming the throttles are opening the same amount as they should.
Hope this helped a bit.
Hi Philip
Thanks for your response, the information you have given me has been very useful, I will be keeping an eye on the air fuel ratios with the AEM 30-4900 gauge I had already purchased.
Thank you Peter
Very nice summary, thank you Philip. If I may ask a “stupid” question – what happens if one were to run in open loop all the time?
On my car, I have been getting DTCs related to fueling (95 XJS with the 6.0L V12). My understanding is that in limp-mode (e.g., whenever a code for O2-sensor is present) the ECU runs of the built-in map and does not use feedback.
I am sure it is not just my imagination – when the CEL is on, the engine is idling better and seems peppier in general.
Steve
Whilst I believe “I know my stuff” around Megasquirt, I do not regard myself as a boffin when it comes to the OEM JAG ECUs, but I’ll still try to address your question from a “common sense” perspective.
Every ECU SHOULD have a fall back mechanism by way of a default fuel map when the lambda sensor(s) fail. This default map is highly likely to err on the rich side of things rather than the lean side in order to ensure survival of the engine (and at the potential demise of any catalytic convertors). I suspect that this is the reason your car feels peppier and idles creamier when in open loop.
I suspect your car feels peppier at partial throttle (where operational lambdas should normally help the ECU target 14.7) whereas in open loop it should run substantially richer, but it should feel much the same at full throttle (where I suspect they run open loop anyway)
The HE engines I played with in the E and the COBRA also wanted to idle with an AFR of not leaner than 13.5 to get a confident, solid, creamy idle. Any leaner than this and they developed occasional misfires.
Philip:
You DO know a lot more than many of us combined and I appreciate the time taken to respond.
Yes, the richness in the AFR is apparent and the reason why the engine runs smoother.
I was just curious because on your checklist, the last bulleted item was “if Lambda sensors were fitted, they need to be present an fully operational”
Well, I am on my 3rd set of O2 sensors - I’ve tried generic ones, BOSCH and NTK – all in less than 5000 miles, to no avail. Find myself driving most of the time in open loop and honestly, if it weren’t for the State inspections, I wouldn’t even try to change it.
I wish I could do what you and Marek have done with MS, but I am not brave/clued-up enough.
Thank again you for your time.
Steve
Steve,
I too am interested in Megasquirt for my car to do away with the distributor (& as a bit of future proofing). If enough 6.0ltr owners were interested/committed to the project, maybe we could pay a sufficiently qualified person to develop a “plug & play” / retrofit Megasquirt kit for our cars.
My car is now manual & the lower weight of the aluminium flywheel & clutch assembly vs. the ring gear & torque converter has made the rolling idle a bit more apparent & a bit more irritating.
Regards
Andy.
I can confirm that the AJ6 engine in XJ40 will run in the absence of O2 feedback.
I recently managed to fry the original ECU in a car that I purchased to do a charity rally from Auckland to Bluff in the South Island of NZ.
The only ECU that I could find in the short time remaining was for a car with O2 sensor (my car was non cat, non O2) the engine would run fine for a short period and then faulter until the ECU realised that there was no feedback. Once that decision had been made it proceeded to drive ok, apart from the fuel economy which was abysmal in comparison to my daily XJ40