I recently bought a 86 XJS. The previous owner was using it as a part car so the car was not running. The car was missing the distributor and several fuel injectors. Other than those the car was pretty much complete so I decided to fix it and put it back to road. I bought a used distributor and a set of refurbished fuel injectors. I installed the distributor yesterday and set the TDC1A position. Today, I installed all fuel injectors with new seals. After I connected everything back, I decided to give it a try. On the first try, the engine cranks normally but didn't start. On the second try, the engine cranked and started but couldn't maintain the idle. The engine was also shaking crazily before it died. I checked the sparks OK and also fuel in the rail and both in and out fuel regulators. I also checked the air intake sensor and the water temperature sensor and the LH. I then tried without the water temperature connected. This time the engine started at the first crank but immediately shoot to a very high idle around 2200 - 2400rpm. I let the engine run at the rpm for about 2 minutes and shut it off, and then to restart, the engine started again still at about 2000 rpm. I then reconnected the water temperature sensor, this time the engine started but got into a very rough and low idle and then died. I then disconnected the water temperature sensor again and started the engine. The engine went back running at around 2000rpm again. There was no misfiring or shaking but just high idles. I decided to let the engine run till it reaches the normal working temperature. Everything seemed OK except the high high idle. And the engine shut off after about 15 minutes running.
I then bought a new water temperature sensor and installed it, but the car was acting as the same: with the water temperature sensor connected, the engine will start to a very rough low idle and shaking and then stop. Without the water temperature sensor connected, the engine will start to a very high idle at about 2000 or 2200rpm keep running at that rpm for about 15 minutes and then shut off.
Can someone help me out of this and tell me what possible things could be causing a problem like this? Steps I need to follow to diagnosis it?
Many thanks!

 

Disconnecting the coolant temp sensor massively increases fueling...to the extent that the normal result is the engine instantly dies. The fact that your engine *likes* the extra fuel, and increases RPM to 2000+, suggests you have a lot of air coming in from....somewhere.

First.....

Are the air cleaner housings removed? Not the clip-on covers but, rather, the bolt-on backing sections. If so, a huge amount of air will come in via the empty bolt holes at the throttle bodies. Varooooom !

Next, are the throttles closing (that is, no mechanical interference), linkages synchronized, and throttle blades gapped to .002" ?

Lots of other 'could be' possibilities; post back

Cheers
DD

 

Hi DD,
Thank you for your prompt reply. Followed your advice, I decided to check the vaccum but didn't find any air leak. Since there was bit oil leaking from the L back, I decided to replace the valve cover gaskets, and reconnect all the vaccum hoses while to remove and reinstall the intake manifolds. Also checked and lubed the Auxiliary Air Valve. Just put everything back and recheck the vaccum, no leak. Started the engine, same thing. While disconnect the coolant temp sensor, engine runs at 2100rpm. I remove the LH air filter, and if I block the hole goes to the Auxiliary Air Valve, the engine will then die. The AAV was tested working properly.


Whatelse can you think I can check for this cause? Thanks!

 

If the engine dies from 2000 RPm when you block off the air feed to the AAV, then you do have a bad AAV, or a leak in an associated hose.

 

Also,

Is the CTS loom plug actually pluggd onto the CTS.

That ATS loom is the same length, and right next door, and soooooo easily mixed up.

How was the AAV deemed "working"???????

Read my sticker at the very top of this section, and you might?? find the answer.

These may assist you in your ventures.

AAV rebuild procedure.pdf

Adjusting the HE TPS.doc

HE Tune up.doc

SETTING THE THROTTLE CAPSTAN AND RODS GRANT.doc

 

Thank you, Grant. I double checked the CTS and ATS looms and they were correctly used, as one harness had a white rubber ring which marked "AIR" with a black color connector that went to the ATS. The CTS harness had a white ring on which a word "Water" was marked. It also has a white color connector instead.
I tested the AAV with boiling water before I put it back. At about 96 degrees, the valve was fully closed deemed its "working"


Anythingelse could cause this problem? The only other thing I touched was the fule injector harness. When I reinstalled the fuel rail and reconnect the fuel injectors, I wasn't sure about the orders. There were no signs and I forgot to mark them when I removed the fuel injector connections. So it was by guessing to differentiate the Bank A harness from the Bank B harness, and to figure out each of the connectors for related fuel injectors to reconnect them. But I don't think this was the issue, as when I checked the rear exhaust pipes when the engine was running at 2100rpm, both sides seemed constantly smooth and there was no sign of misfiring at either bank.
Anythingelse could be the cause of tis problem?

 

OK,

The injectors are in 4 groups of 3.
1,3,5A 2,4,6A 1,3,5B 2,4,6B.

I doubt that is the issue, but getting it as it should be removes another "maybe" from the list.

The fact it runs with the CTS unplugged is not normal. Take a normal running V12, unplug the CTS = dead V12.

Does your market/car have the stupid 15 minute timer fiasco??. That runs the engine at about 1500rpm or so (I really do forget now), and is just silly, and needs unplugging.

The AAV should give 1200 or so cold, and as the piston closes the mouth the idle will be adjustable with that 13mm bolt, and settle at 700ish.

The 90deg elbow on top of the AAV is known to split on the underside, huge vac leak.

Inlet gaskets also tend to lose section, huge vac leak.

Then the ECU itself becomes suspect. 1986 would have what is known as a 6CU unit, and they are troublesome now. BUT, they only control fuel injector pulse time, and if its supplying longer pulses (richer mixture), unless there is heaps of air available it will stall out.

Each section needs systematic checking, and sorting.

What timing degree is it set at static, should be 10deg. It will run and rev with more than that, which can confuse things.

Throttle discs not closing, comes into the mix, but that CTS unplugged running is a strange one.

Maybe try bridging the terminals inside the CTS plug, that will fool the ECU to a HOT engine, and may prove nothing, but worth a try.

 

Thank you, Grant.


I was thinking about that 15minutes delay thing but didn't know where to find it. But even the car has it equipped, it only explains why the engine shuts off after running at the high idle for about 15 minutes. It shouldn't be the cause of that the engine needs to have the CTS unplugged in order to run. Timing was set at 10 degrees BTDC ( I read your articles before this restoration, THANKS!)


It seems the cause may still be tracked back to air leaking. I am going to undo everything today and make sure all the hose connections are good to rule out any possible air leaks before trying on a different ECU (I do have a 16cu spare one I collected years ago)

 

Just for gigles.

At the front of each inlet manifold are "over run" valves. Under the alloy dome thingies. Check that the valves are actually installed, and closed off.

I remove them, and simply plate the manifold.

The revs you are seeing is a huge leak, and all the small hoses combined would not give that number.

A ruptured brake booster diaphragm will, so isolate it from the system for now.

The 16CU is plug and play, and takes 5 minutes, so I would swap it out, and another maybe off the list.

Trace the wiring loom from the CTS back where it travels behind the LH air cleaner, there are a few splices in there, and soldered, and taped, maybe the tape has failed and the splices are shorting the signal to the ECU.

I have an ECU pinout table if you need it to check each wire from the ECU to the related item in the engine bay. Let me know if you want it.

 

Thank you, Grant. Yes, please let me have the ECU pinout table that will greatly help. Also, if I swap the ECU now (without know the real cause of this problem, would it cause collateral damage to the new ECU as I don't want to loose that 16cu I collected. It's now very hard and expensive to find it on the market :-))


Thanks,

 

OK, maybe a good idea to check a lot of stuff first, but that ECU, if it is a 6CU is going to remain suspect.

Here is the chart I use for the engine fire ones I have rebirthed.

XJ-S ECU Pinout table.doc

 

OK, updates:


1. I redid everything this morning. Removed everything down to the valve covers. Checked the 10 degree BTDC on 1A. Carefully checked each fuel injector connectors, all good;
2. Removed both side intake manifold and checked all bolts that go on them, all good (I even quickly repaint them with the high temperature paint now they look shinny beautiful; while they were off, I removed the AAV and double checked it again with boiling water, Good!
3. Reinstalled both side intake manifolds and added thin layer of silicone sealant on the gaskets ( I reused old ones). everything was tight and good.
4. reconnected all vacuum hoses back on
5. reinstalled the fuel rail and connected the fuel pipes;
6. reconnected all fuel injectors and spark plug wires.


With everything back, I tried, but again, same thing, bad idle shaking with the CTS connected and high high idle when its disconnected.


So I decided to transfer my focus on to the ECU. Like Grant suggested, it's a 5 minutes swap. And guess what, after I changed the ECU, the car started at the first try (with the CTS connected), it idled at about 1800rpm for about one minute and then gradually down to about 1000rpm. It clearly confirmed a faulty ECU!


I guess the ECU was the root of the cause though the symptom didn't immediately pointed to that, and I guess that's why the original owner didn't fix the problem and decided to get rid of it. Thank you Grant for pointing this out.


Now I will clean up everything and hope to enjoy the ride over the weekend.


Thanks to you all.

 

Glad you're all sorted but I'm not sure why the ECU fixed it. But, I won't argue with success

Cheers
DD

 

Hi Doug - Me neither, and that's why I didn't think to replace the ECU though I had a spare one. The only explanation is that the ECU outputs less fuel time with the standard CTS input so disconnecting the CTS let ECU output more fuel than the car normally requires. And there could be somehow air leakage from the throttles and I never checked the gap, so the engine can keeping running at 2100rpm for 15 minutes till the 15 minutes cutoff triggered.
I will put the faulty 6CU ECU on my 1987 VandenPlas to test if it acts the same and let you know..
Thanks,

 

Well done.

I also have no answer for that CTS issue doing what it did.

I really reckon that 15 minute thing should go.