'86 XJ-S 5.3 US spec 11.5:1 with Lucas ignition and 16cu here.


Ok, I have struggled to overcome a poor idle for over a year. I thought a recent ECU vacuum line refurb might do the trick, but no joy. Here's what I've done so far. I really hope that someone has some suggestion for me! I'm thinking of buying an adjustable FPR and trying to correct the rich condition by reducing the fuel pressure, but I'd much rather understand what could be making it run rich to begin with.

As far as I can tell, I am still running rich even with the ECU adjusted lean. I have assured myself that my adjustment is in the correct direction. Set to the middle of the range you can smell the richness increase and the idle deteriorates even more. Max lean is almost enough to settle it.

This is all at idle at rest, so no closed loop. Not an O2 sensor failure. It's also the same at idle when in gear or with the link removed.

I do note that the idle is almost perfect when I first start her from cold. It deteriorates soon after starting ( prior to reaching temp - AAV still open ) and at temperature it is worse, but stays the same. It does not come and go or significantly change after the first couple minutes.

What's the best tool for me to purchase to read the exhaust mixture? I don't want to be dead wrong in my thinking its rich. I'm basing a lot on the exhausts smell, I'd like more precise info on the mixture and I seem to can't make sense of the pattern of the O2 sensor circuits voltage wobble.

Fuel system:
New Pump - Bosch
New filter - Mann
New sump filter
Tank removed and cleaned. Good condition. No rust.
A bank FPR delete
New supply line to rail
New B FPR - Bosch
36psi @ idle
All injector hoses replaced.
All injectors cleaned, tested
4 injectors replaced
All injector seals replaced
TPS @ .33v
New Premium fuel
ECU idle adjustment at extreme LEAN end of adjustment.

Air system:
New filters
Intake manifold re torqued to spec
Vacuum lines replaced
Vacuum caps replaced
Vacuum advance tested good
Vacuum dump valve, regulator tested good
New ECU vacuum hoses
overrun valves deleted
Cats in downpipes and main cats deleted
Fuel evap canister and connections deleted
18in hg @ idle
New O2 sensors. - single wire ( originals were 1 wire )
Compression test - good, minor variations cyl to cyl

Ignition system:
Injector loom checked good.
Loom connector plug cleaned
Resistor pack connector cleaned.
All injectors tick
All injectors fire on throttle punch - visually confirmed
New single coil - Jaguar
New plugs - NGK BPR6EF
New HT leads - Taylor 10.4mm
New dizzy cap
New rotor
Dizzy pickup gap set to spec
New amp module
Removed capacitor in amp
Shielded ECU wire tested - good

 

JJ

Is it both banks or just one?
Have you tried just a single vac tube from the spigot under A bank TB direct to the vac capsule, blocking off ALL, absolutely ALL other tiny hoses?
Second, pull the wires off the enrichment thermo switch on A bank rear water manifold to disable that system
Any chance of a video/sound bite of the problem?
Also, have you blown out the fuel return line to the tank. If this is blocked for some reason it can lead to a rich condition.
At exactly what revs does the engine smooth out? It is just possible a slightly blocked exhaust (eg bad baffle) could affect the idle.
Greg

 

Both banks are affected. Random chuffing at exhaust but not "poofing" like it was at richer settings. I do have audio recordings. I'll upload.

I have run it with vac adv hooked directly to the upper spigot. I think I recall that correctly. Lower tap is always vac right? Upper is variable with throttle? Or do I have that flipped?

This did not resolve the idle, but that was many changes ago. Will try this again.

I have NOT blown out the return fuel line. If it were clogged and causing a rich condition I would expect high fuel pressure correct?

The cats have been removed after a partial melt. I suppose it could be muffler restrictions, but at idle this should not matter. Should it?

Smooth running over 1500 rpm or so. Maybe less.

I don't have an enrichment switch on the A bank water rail that I know of. Do I?

makes me question the capstan enrichment switch. Checked that but it's been a while. Should probably re-test the vac WOT sensor too.

 

JJ
Put the single vac line to the spigot under the A bank TB, just to test.
You should find two wires attached to a switch fitted to the rear A bank water manifold (see pic attached). Remove them and test.
Here is an off the wall test: remove the cross pipe at the rear of the engine from which the vac line to the ECU goes. Then block off ONE bank where the cross pipe attaches to the manifold and connect the cross pipe to the other manifold (The free end having been blocked also). So the ECU is seeing vac from ONE manifold only. Then reverse the attachment end and thus test both banks. The tickover may be a bit low with the AAV bank disconnected, but warm it up and see what gives.
I take it the air injection system is not fitted?
Finally, for now, have you disconnected and plugged the CCV system?
Greg

 

No electrical switches that I recal on my water rail. No pic attached, maybe if I see yours I will recall it.

Air injection rails removed, ports plugged. Pump dumped.

CCV removed. Along with the canister and ancillary connections.
EDIT: I hope I'm reading that acronym correctly.

ill try the vac advance source move after lunch. Balance pipe test will have to wait for more time.

 

What does the vacuum measure at idle? Did you gut the cats that are part of the manifold as well as the separate ones?

 

18 in hg. Yep, downpipe cats and the big 'uns are gone.

In a bit of serendipity, I happened on a thread that linked to some info from "the book" about a poor ground on the ECU causing a rich running condition up to and including rich enough to fail to start.

Now that's something I can bite on. I'll be testing ECU grounds as soon as I get her home.

Greg,
I couldn't check the lower vac tap setup after lunch. She was too hot. In the morning!

 

jj,

sorry i don't have suggestions for your idle problem (yet). But wanted to report my vacuum at idle holds at 21hg. (Wanted to test long time ago, but only recently got my vacuum tester)

 

AEM 30-4110 Summit and others carry it.

 

It does sound rich if it runs well cold and deteriorates as it warms up. The fact that you have melted the catalysts says that a lot of raw fuel has been going through them.

Regarding Greg's suggestion of an enrichment switch, I think that's European emissions. The emissions equipment and vac piping is quite different between US/Canadian cars and European cars.

Vac level at idle sounds reasonable to me. It will vary with elevation, as the higher up you are, the less air pressure there is, so a lower level of vacuum can be produced. I can only get about 16" Hg for example at 3500'. I can only get over 20" coasting downhill at speed on a closed throttle. Sea level spec is 17.5" Hg at 800 rpm idle, AC off, so you are good there.

How were the injectors tested and verified that they are not leaking and performing to spec? SD Faircloth has been well respected for his servicing of injectors on the Jag-Lovers lists.

I'm wondering about the fuel pressure regulator delete? Originally they were different pressures on each side; inlet 45psi, outlet 36. Spec is measured downstream of the inlet regulator (i.e. rail pressure) at idle is 28.5-30 psi. There is also the fuel rail thermal vacuum valve that applies maximum fuel pressure at high fuel temps to combat vapour lock. Out of curiosity, does your AC work? There is a fuel cooler incorporated into the AC system.

Have you verified that the timing is correct? 18 degrees BTDC@3000 rpm? That works out to approximately 0 TDC at 750 rpm, but the spec is at 3000 rpm.

Have you verified the coolant temp sender output to the ECU is correct? As a quick and dirty test with the engine warm, unplug the connector at the temp sender and place an piece of wire across the terminals on the harness to short them - an unbent paperclip works well. That should tell the ECU it's "full hot" and should remove any temperature based enrichment.

If you can, it's worth reading manual S-58: http://www.jagrepair.com/images/Elec...ance%20S58.pdf

 

JJ
Pic attached. See the switch screwed into the manifold on the left of the pic, just in front of the heater take off.
Delete of A bank FR nothing to do with the problem I am 100% sure.
I am pretty sure all US spec cars have this water rail switch, it is just the duration of the enrichment timer that changes. Just pull off the connectors.

 

You will have two wide open throttle enrichment switches: One on the back of the capstan which is acted upon directly by the capstan, and the vacuum WOT switch on A bank manifold, cabin end.
Engine running, they should have power to one of the wires connected to them. At WOT the switch makes contact and earths the system which enriches the fuel. Test that the switches are open at normal tickover, one might have failed. They are wired in parallel, so either of them if closed earths the system and activates the enrichment.
Greg

 

Yet another "bright idea":
While doing the "blank off the cross pipe" test, having done it as described, if no change try this:


Disconnect the throttle rod from one bank, and remove the injector loom clips from that bank's injectors. Then start and see what the tickover is like with only one bank getting fuel. Repeat for the other side.
Greg

 

Adding to Gregs stella list.

I would disconnect all the vac items except the distributor advance unit, and ECU line. Plug any spare lines to prevent vac leaks.

The "full fuel" enrichment vac switch is a tad suspect to me. They do fail, I have 3 here that do not hold vac, and if that occurs the system will richen the mixture by approx 10%, maybe more. Not so bad up the rev range, maybe 1800 and beyond, but at idle, oh boy. You MUST disconnect that switch electrically to rid the system of its application. Simply removing the vac line, closes the contacts and earths the fuel map, and rich it will be.

With all that emission rubbish gone you can advance that timing quite a ways. I always start at 10 BTDC, vac capsule attached via the lower spigot of the RH throttle body (vac advance at idle and cruise), and then advance from there until it pings, then back it off. Basically, thats how the car will be driven, so why not time it in that mode??

I dont run the timing plates either, one less oil leak to deal with.

This is what I wrote up a long time back.

Trimming the timing on a running V12.pdf

 

Hello everyone! It's been a while since I posted on this. My apologies for keeping everyone in suspense for so long. I have been very busy over the past couple weeks and haven't been able to work on the Jag to test all these wonderful suggestions. But I have a surprise!

I had a bit of time available yesterday, so I started doing some tests. First I wanted to confirm that the ECU is not being told it needs to enrich the mix by the capstan or vacuum switches. Both test fine. I checked their connection to the ECU connector as well. Good.

Next I wanted to test both the CTS and AirTS. I jumped them both out with custom jumpers I made for them. No change in the idle. Disconnect the CTS jumper and the engine wants to die. Disconnect the ATS and the engine revs a bit. Ok.

The only other thing I could think of that ties in to enrichment is the Fuel temp switch. I don't have one though. Mine was broken off when I got the car. The switch had been just laying on the intake. I had disconnected it and, following the advice I'd found on this site, I had connected the two bullet connectors from the switch together.

I decided to disconnect this pair of bullet connectors and cranked the car.

It ran, of course, but it ran, better. Much better! WTH?! It's not missing. It's smooth. But... But it's been rich! It should be worse! Lemme drive it. That will be worse for sure. Nope! Runs great! Pulls harder, smoother, exhaust doesn't have that odd plufffuuuhhhh... sound that I assumed was the unburnt fuel igniting as it exited a cylinder.

I've run it down to South Carolina, it's powerful. Better than it's ever run. I'm getting to run into town and that's a 70mph stretch. I'll report back after a bit of Italian tune-up.

I do not understand at all. This doesn't make any sense to me.

 

JJ
I hope it was not me who gave you that advice! By connecting the leads to the fuel enrichment switch I think, repeat think, you permanently told the ECU that the car was cold! Thus overfuelled all the time. Separating the leads put things back to rights. WELL DONE. Great when they get fixed, isn't it?
Greg

 

Greg, as a matter of fact, I do think that it was you! But, to be honest, Inthink you were right.

Reading the wiring diagram, the fuel temp sensor appears to be normally closed, and breaking that circuit with hot fuel should be the same as pulling the connector off the air temp sensor. High ( infinite ) resistance, and subsequent enrichment.

Im thinking the rich fuel is just masking the behavior. I still feel a miss at idle. An improvement that confounds my mental model of what's going on.

 

Not guilty!
greg

 

Right you are. It was another Greg.

Can anyone tell me absolutely is the fuel temperature switch was normally closed and opened at temperature?

 

My understanding from a very long time ago.

The fuel switch on the rail, Aussie version, was an electrical thermo switch, with Normally Open contacts.

As the temp got to the pre set point, the contacts closed, thus earthing the same circuit as the "full fuel/throttle capstan micro", and providing a slightly richer fuel mixture which was meant to aid "hot start" issues in markets other than OZ.

Some markets had a vac attachment, that "T'd" into the LH FPR vac hose, and simplistically dumped vac as the switch opened the port, which prevented that FPR from modulating the fuel pressure to a lower PSI, and this was was meant to give a "flushing" affect to the then HOT rail, and cool it down, to stop hard starting issues in other markets.

I dont believe either worked particularly well, and are mostly removed, mostly after breaking.

Joining the wires would effectively do the same as a HOT switch mode, and allow a richer fuel mixture, thinking the engine has a HOT rail.

All info on deleting that switch, electrical style, is to simply insulate the 2 wires and tuck them out of sight until the engine loom is rebuilt, at which time they can be eliminated.