Hi All,

I haven't been around the traps in a while!

We can blame the normal culprits - life, work, and such.

I recently acquired a rather nice 1988 Sovereign V12 - some pictures and further information will follow in due course.

Having not run for 15 years there was a few stuck injectors and hoses to be replaced. I managed to run the car for short time and all the vitals looked good, however, the car was running VERY rich - so rich that there was a plumb of black smoke filling the garage within seconds.

I removed the injectors and flow test them on a rather primitive rig - all normal and no leaks under pressure. All earths are clean and good, battery voltage is good.
Fuel pressure was around 35 psi so all looks good. I cant see any other real issues

The car has o2 sensors for what its worth - cant see that as the issue.

I have looked for information on simular rich running conditions, but haven't found much that relates to the cars behaviour.

How does the ECU's vacuum reference relate?

Does anyone have any advice on where to go from here?

Thanks for the assistance

Jay

 

A couple somewhat notorious possibilities.....

The coolant temp sensor for the ECU. Mounted just aft of the LH thermostat. If skewed 'cold' when the engine is warm, you'll be over-fueled. Easy and cheap to replace as a guess but can be checked with an ohm meter if you have one. We have the specs.

There is a vacuum line from the balance tube at the rear of the engine that runs all the back to the ECU in the boot. If leaking or broken, you'll run rich. Pull the line at the ECU and make sure you're getting full engine vacuum

There are other possibilities but this is where I'd begin

Cheers
DD

 

+++ what Doug mentions.

AND

The TPS is out of adjustment, and/or going flaky.
The Full Load Fuel switch/s are stuck. There are 2, one on the capstan as a micro switch, and activated at about 2/3 throttle opening. The 2nd is teh Blue/White vac/electric switch, usually tucked near the 5A Inlet trac, and it requires VAC to keep the contacts OPEN, and the fuel system in "normal" mode. They fail, and when the vac diaphragm allows vac leakage, the contacts close, and the system will richen by about 15%. Both switches are wired together, so either one can and will, richen the beast for acceleration.

The ECU works simply on MORE vac, LESS fuel, LESS vac, MORE fuel, SIMPLISTICALLY as I said.

Is it rich at idle, or rich in general??

 

Thanks for the advice Gents!

Just to give some more history on the car - it had been in with some amateur mechanics... the timing was 50deg advanced and there was loose vac lines and wiring everywhere.

I retimed it today and removed / plugged up all of the loose / rotten vac lines. It currently doesn't have the vac advance connected but I figure that is a future problem

I ran the car for a little longer (seeing as it no longer sounds like a machine gun since I fixed the timing) and it was still rich. It is hunting from about 500RPM to 2000RPM and back again at 5 second intervals. I haven't tried to rev it up (thinking of the neighbours given it was about 8pm...)

The coolant temp sensor reads 2.5k ohms. The air temp sensor was something simular for what its worth.

I shorted the CTS and ran the car with no improvement.

I also disconnected the full load switches (assuming they are normally open) with no improvement

The line in the boot does have vacuum - I didn't have time to put the gauge on it (I will tomorrow to confirm).

Where to next from here?

Appreciate the assistance - another V12 soon to be back on the road

Jay

 

TPS
Throttle rod settings
Throttle disc settings
AAV stuck.
Distributor mechanical advance stuck, Common as Fosters.
Timing may need trimming some more.

Some attached light reading, grab a slab a have a read.

 

I have to ask, just to make sure.....

Did you thoroughly drain the 15 year old gas and replace with fresh?

Stale gas will smoke like crazy. Even fresh gas will, if partially contaminated with what's left of the old stuff

Cheers
DD

 

Thanks Gents,

Thanks for the literature - its very informative

I did drain, flush and renew the petrol. Also purged the system and replaced filters, etc.

I adjusted the TPS but i figure it is probably past it as it was very finicky and went out of adjustment fairly quickly after cycling it a few times. If you snapped it closed it seemed to settle back at 0.35 v consistently, but a slow closing could result in anything from 0.25 to 0.4 v.

even when reading 0.35v the engine was still surging. I also blocked off the AAV - no change to the surging. throttle plates / adjustment checked out O.K. Checked dist. advance - all ok.

It seemed to run a bit better after adjusting the TPS but it then invented a new way to fail - it would crank but not start for a long time, then start, run for a few seconds (badly), and then die.

I checked and there is fuel returning to the tank (indicating that its not a lack of fuel)

I found if I flicked the TPS half a dozen times (pulsing the injectors), it would fire right up and die again. It does have spark when it refuses to start.

I checked with an oscilloscope while it was cranking (but not starting) and I couldn't detect an injector pulse.

I ended up pulling the whole fuel / intake system off to clean and repaint the cam covers, and make sure there are no other vacuum leaks ( i am suspect on the injector seals). The wiring also needs a general clean up

Starting to look like an wiring or ECU issue? how often do the ECU's fail in these cars and do these symptoms sound like a known failure mode?

Anything else that would cause it to momentarily loose injector pulse ? (bearing in mind the injectors will pulse with the TPS)

Any links to a good wiring diagram so I can start back probing? (i've found the standard one but the resolution isn't good enough to read the fine text)

P.s. - its an lambda / o2 sensor car, in case that makes a difference

Sorry for the drawn out posts - and that for the help

Jay

 

Jay,

Well done so far.

Yes, the TPS is dying, but I doubt at this point it is the root cause.

With the AAV blocked off, I would expected a stall situation, so maybe you have a vac leak that is reeking havoc. The 90deg elbow on top of the AAV is a known culprit. The PCV valve is next,
The hose/pipe that runs from the balance pipe to the ECU can be clogged. Remove it both ends, and flush it with Carby Cleaner and compressed air, ensuring GUNK goe into a rag and not all over the carpets in the boot. Then reattach it to the ECU, and see it it passes the suck test, as in it holds vac. Many I have dealt with over the years have had oily goo in that pipe, and some do not hold Vac.

NO IDEA on the S3 cars, maybe the same as the XJS cars. On the inner guard, RH side, outboard of the radiator is the EFI resistor pack. About the size of packet of smokes, and has a Multi Pin plug inserted from the bottom. Remove that plug, clean the plug and the socket, do it again, then flush with solvent ( I use Carby Cleaner p/pack), as it dries with NO residue. Removing that pack can be tricky, but well worth the extra beer or 2. This item is now becoming more of a problem than before. There are NO moving parts inside it, and they DO NOT fail as such, just the connection to the loom.

The EFI loom itself, fastened in the bottom of the "V" is very high on my list now I know what you have done.. They are failing more and more, and age it not on their side now. Dont repair it, replace it, either buy one (oops), or do what most do, make your own, and secure it up on the fuel rail, away from the ehat.

The ECU in a 1988 car would be a 16CU spec unit, and basically bullet proof. I suggest removing the multi pin plug, clean the plug and socket, as you did with the Resistor Pack. I have had some with "green growth" in that plug. I use Lemon Juice, the real stuff, as a cleaner.

My money is on the loom, Resistor pack plug, ECU in that order.

The Lambda in that year is a minor trimmer, and I doubt it is doing much at all.

The dreaded Coax Shielded Wire, from the Ignition Amp to Pin #18 of the ECU, may be having a female moment. That sucker is the ONLY signal from the Ignition system to the ECU to inform the ECU that there is Ignition Pulse, so keep the Injectors firing. Loose that signal, and the beast be dead. They rarely go intermittent, and would NOT cause a surge, usually ON or OFF.

 

I had a V12 running very rich, and it was the injector harness ground; one of several eyelets under a bolt near the battery (on my LHD car).

I cleaned them up, and good to go.

Rob

 

I have a Series II 1976 XJ12 that was running very rich, turned out to be the rubber elbow below the intake coming from the AAV. When running it would collapse. Not running it would look fine, the rubber was very soft and the little bit of vacuum created while the butterfly was closed would make it close off. Just a thought.

 

VERY common, sadly only related to the PreHE engine. The HE is quite different.

Good thought all the same.

 

VERY common, sadly only related to the PreHE engine. The HE is quite different.

Good thought all the same.

 

Hi Gents,

In the spirit of closing this out for the future reader, I ended up overcoming the issue by:

• Someone had adjusted the ECU trim full rich (probably accounting for vac leaks that i subsequently fixed?)
• Coolant temp sensor was replaced and flaky wiring fixed
• Replaced the flaky TPS
• fixed all the vac leaks and adjusted the AAV / Throttle butterflies

In the mix of the above, it now runs well but has a hot start issue as discussed in the next thread.

Thanks for the assistance everyone!

Jay