I’ve written a few times on the forum relating to issues on my 1985 XJ12, but once an issue gets resolved a new one pops up (see e.g. thread relating to galloping after distributor service.
My current issue is as follows:
- Misfire on both banks.
- Somewhat difficult to start, needs throttle input first time starting to get to an idle, but retains idle once started.
- Serious shaking due to the misfires.
During the past winter I serviced all injectors with the Mr. Injector overhaul kit, i.e. new filters and hoses. During the service I also tested the injectors, all hold under pressure, give a decently uniform flow rate, and work as expected. All injectors also seem to fire when mounted in the car.
Distributor cap and rotor changed. Old rotor had a few mm. wiggle when mounted, and old cap was over a decade old. Spark plug leads have also been changed. Coil was changed for single style coil from SNG, although it seemed to struggle to produce a nice spark. Old dual coil system back in the car, with nice spark.
Spark plugs were changed a few thousand km. ago, but were removed to check and re-gap. Given the issue with the coil and the difficulty in starting, they reeked of fuel and were noticeably wet. Spark plugs were cleaned with brake cleaner and a hard toothbrush as well as re-gapped to correct spec.
Compression was checked a while back, with all cylinders seeming to perform well, all in the 200psi range, with one (B2) down at approx. 170 psi. Will most likely do a recheck of compression in the upcoming days.
Timing was checked and set to approx. 20* BTDC @ 3000rpm, with vacuum advance disconnected. I’ll recheck the timing given that 20* is a bit too advanced, however, I don’t really feel comfortable doing it before the misfire issue has been, at least somewhat, resolved.
Once running the engine responds well to throttle, rising freely and rapidly in RPM with throttle input; however misfire persists in all rpm’s. No known vacuum leaks, and can’t really hear hissing around the engine bay. Idle is at approx. 750rpm when warm and slightly above 1000 cold, AAV has been removed and appears to function correctly. Butterfly valves correctly set and cleaned.
TPS was recently changed to the newer version, but measures slightly below 0.3v, rises correctly up to about 5v with WOT. When giving throttle, and exceeding 3500rpm (although briefly), A bank gives off black smoke, unclear if it’s due to sitting without driving, or if it’s unburnt fuel.
A few more observations:
- CTS measures correctly with engine heating up.
- Intake temp. sensor seems to be a CTS, measures 2.4kohm. Engine appears to run more rough when disconnected; but there appears to be no difference between plugging it in to the sensor or shorting it directly.
- No difference when removing vacuum from FPR’s (except for increased idle, which goes away when covering the hose).
- TPS and CTS wires to ECU appear to be intact when measuring resistance and continuity at the ECU connector.
To further diagnose the issue I’d need some help from you, namely:
- How can I track down which cylinders are misfiring?
I’d like to avoid just pulling plugs and seeing if anything changes, since last time I did that the HEI module started acting up (difficult to find a replacement which wouldn’t overheat) and my rev. counter died and I had to buy a new one.
- Where can I measure fuel pressure on the V12 HE?
I’d like to measure it post-injectors, since It’d be easier to depressurise the system, and since, in theory, it’s the fuel pressure post-injectors which would indicate if any of them are leaking, and if they are actually getting good pressure. I can’t seem to find a good place to measure the pressure, since all hoses on the right hand side seem to have specialised fittings.
Furthermore, do you know of any issues which would/could cause similar problems? I’ve had trouble finding any similar posts on this forum or other forums.