Ultra-rich condition in 87 XJ6

XJ
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Got the '87 XJ6 back from the shop today because the shop can’t figure it out and has reached the end of their rope. We’re a little hamstrung because we lack the tools to completely diagnose the problem and are in the throwing-parts-at-it stage.

This is what has been thrown at it so far:

  • One complete, new set of injectors
  • Two sets of spark plugs
  • Cap & rotor + 2 sets of plug wires
  • 2 coolant temp sensors
  • 1 airflow meter from Everyday XJ (used)
  • Cleaned/reoiled the K&N air filter

EDIT: I also forgot the following has been changed/replaced:

  • Cold start solenoid (twice)
  • Fuel pressure regulator

The car basically is a brick. It is dumping black smoke out both tailpipes. It builds revs very slowly and is hesitant to rev beyond 3,000 rpm, but will do it. It will not pull a hill of any kind. The in-dash computer, which I’ve found to be quite accurate on these cars, is reading MPG of between 5-12.

We also believe now that the catalytic converter has been ruined from all the raw gas being dumped into it. At the end of a 10-minute drive this afternoon, it began dying at stop signs, and it had trouble going up a 2-foot incline (no exaggeration) into my garage. When it finally got in the garage, I was greeted with a strong smell of unburned fuel and catalytic converter.

I have no shop around here that has Jaguar diagnostic tools from a S3 car, so we’re stuck in that regard. The shop wants me to get another airflow meter, or maybe a new computer. Something is causing the car to dump raw gas, wide open at all times. The car actually runs BETTER if you disconnect three of the fuel injectors.

As simple as these cars are, there doesn’t seem to be a lot of components involved in this problem. It would seem to me it’s either a computer issue, airflow meter issue or there’s compromised wiring somewhere. I’m open to suggestions here but as you can see from the list above, we’ve already thrown quite a bit at it.

Jess

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Did they not look at the coolant sensor?
Edit, overlooked.
Injectors won’t do it. The trip computer knows about it so it isn’t the separate cold start injector but the engine does think it’s cold or consumes tons of air.
Try disconnecting the coolant temp sensor (not to gauge but the one with the bosch plug), does it die?
What is the fuel pressure? Take the brown switch on the fuel line out of the equation by directly connecting the pressure regulator to manifold vacuum. Make sure the fuel return isn’t blocked.
One set of 3 injectors grounded, unlikely. Does it idle ok?
Welcome to the forum and good luck. The cat converter may be shot by now.
David

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David,

Thanks for the response. You reminded me that we’d also replaced the cold start solenoid/injector and the fuel pressure regulator.

I will try undoing the CTS later tonight after it cools down a bit. The cat, I’m sure, is clogged badly. I’ve got to wait until it, too, cools off a bit for the passageways to open up enough.

It idled OK until everything heated up and then it slowly got worse. This car has never been a great idler since I’ve had it, though. It sort of lopes like it has a big cam in it.

But 3 months ago, I was getting 24 mpg on the interstate. The reason I knew I had a problem is I started having to fill up more often and checked my MPG on the computer and it was running around 16-17. Now it can’t get over 12, so this is a deteriorating condition for sure.

Jess

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I read that you changed spark plugs - question - what gap are you using on the spark plugs - almost sounds like you may have too large of a gap on the spark plugs since seems to not be burning all the fuel - evident in the black exhaust and the failure to increase revs under load going uphill and the excessive smell of fuel - just a THOUGHT.

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I’m not sure where the shop gapped them, but remember that the problem started suddenly with the old set of plugs/wires in it. So for it to have started so abruptly, I don’t think the gapping on the old plugs would suddenly have been the problem (same for plug wires, cap and rotor).

This feels more like sensor failure, or something internal to the airflow meter, computer or wiring in between the two. Also, I don’t think we have replaced the O2 sensor yet.

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Had a similar issue years ago with an XJ6 and it turned out to be a bad battery! I wouldn’t have believed it either, but, it worked! We’d made some phone calls and were told this by a jaguar dealer!

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I had similar situation with my V12…turned out to be bad ECU.

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I can believe a bad battery, but the ECU rarely fails and has no internal pressure sensors etc. that can break, unlike the V12.

If it idles ok and gets way rich when in gear (closed loop) it can be a misfire causing the mixture to be perceived lean, then it’s fattening the mixture to compensate. Which could be ignition related in the end.
That is a common issue your shop should be knowing about. When they throw parts at your cars always keep what they tore out despite working fine. Put a multimeter to the coolant sensor (values here on the forum) and learn what disconnecting the o2 does because I don’t know what an XJ6 does. Make a „stall test“ when warmed up and immediately pull the plugs and take pictures of them.

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I presume it has electrolytic caps, though. Those things are notorious for causing issues with age. They’re so cheap that some advocate just opening the case, warming up the soldering iron and replacing all of them just to see if it helps.

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**
Have you actually measured the resistance between the pins on the CTS, Jess…?

It’s purpose is to vary mixture with engine temps; a cold engine needs richer mixture, leaning out as engine warms up. You are certainly running too rich, but maybe not so right about ‘few components’ being involved. What you need is some basic diagnostic tools, in this case; a multimeter and a vacuum gauge. Most components and their actions can be easily checked out. Swapping components is fair enough, but only if they are verified as working - and ‘new’ does not mean that they are…

After checking the CTS resistance; check resistance between the two wires on its connector. It should read some 2 Kohm - but importantly; there should be no variations when the connector/wires are bent and twisted. This test verifies connection to the ECU…

Clamp the CSI hose; it will positively eliminate any fuel delivery from this source. If no change; the CSI is innocent - but fault finding is as much about verifying which components work as which do not. Working components cause no faults…:slight_smile:

As per David; open the filler lids and verify, with the pump running, that you can hear fuel returning. If fuel return is blocked; the fuel pressure will rise - which certainly causes overfueling…

Disconnect the vacuum hose at the fuel pressure regulator and run the pump; there should be no fuel leaking out - if it does; the replacement regulator is faulty. With the engine idling; connect the vacuum gauge to the hose - ‘normal’ reading is some 15 - 18" Hg. You probably have very low idle vacuum, then increase rpms to some 1500 rpms - then to 2000 etc. At steady rpms the vacuum readings, high or low, should be steady; if vacuum gradually drops - it indicates clogged exhaust/cat.

Have you actually checked spark quality? Use a spare spark plug, triple gapped, connected to any plug lead and crank. The spark should be strong and blue - and while the shop certainly should have checked ignition (and indeed ign timing) testing it yourself is simple. Likewise; it would be very remiss of the shop not to verify fuel pressure - but they would not change, or recommend changing, the fuel pressure regulator if pressure was to spec…

With the engine idling; disconnect the multiplug on the AFM, observing changes. Which are not conclusive, but there seems to be some sort of ECU fall-back fueling when the AFM is faulty…

Fuel consumption while driving is somewhat inconclusive - with a fault we tend to push pedal for more power, and fuel consumption will increase.

I very much suspect a clogged exhaust, although the shop should certainly have checked this. Plain overfueling should not in itself limit rpms; the engine burns the amount of fuel the air allow and eject the rest of the fuel unburnt. However, a clogged exhaust will gradually build up back pressure, limiting rpms and power - the engine may idle ‘fairly well’. That the problem has gradually increased also points toward this diagnosis - clogging begets more clogging…

The crude way of verifying this is to disconnect the downpipe from the manifold. It is extremely noisy, but conclusive…

Ultimately, the ECU may be the culprit - though it is very reliable it cannot be conclusively eliminated except by swapping it with a working one…

Frank
xj6 85 Sov Europe (UK/NZ)

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I have to correct myself, if it’s idling well, fuel return can be ruled out. Pressure regulator to manifold is unlikely but worth a try.

If the problem can be switched on and off by putting it into gear it should be a lambda issue, cause to be found. Clogged exhaust is possible.

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Hello again everyone,

Just wanted to update you: After several months, if not years of trying to fix this problem, and it finally coming to a head recently, we have fixed her and gotten her back on the road. I wanted to update everyone with what the problem was.

Many months (years?) ago, we had a leaking cold start injector, the original one on the car. So we ordered a new one. Not remanufactured, not off a “known running” car, but a brand-new, out-of-the-box-from-Jaguar cold start injector.

In the course of trying the simplest things first, and working from a list of everyone’s suggestions both here and on Jaguar Forums, we simply clamped off the fuel supply line to the cold start injector. And that completely fixed the problem. No more running rich. No black smoke. No having to feather the accelerator to start it in the mornings.

The injector was stuck open, apparently, whether or not its wiring harness was plugged in. So we disconnected the fuel supply line entirely, blocked it off properly, and the car runs great. MPG is back within factory specs.

I’m not sure why a BRAND NEW cold start injector would be nonworking out of the box, but that’s what the problem was. Given that I live in Alabama, and we only have a true “cold start” situation for 3-4 weeks out of the year, I think I can live without the CSI. Thanks to everyone for helping us track this down. She’s back on the road now.

Jess

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Soaking it and passing some injector cleaner through it and exercising it with (vey) short 12v pulses might unstuck it.

Known problem with injectors that stayed at the shelf for a long time.

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The cold start injector can take 12V. It will get hot eventually but all the system does is switch 12V to the injector for several seconds depending on how cold it is.

Once it’s stuck closed it’s not repairable. Don’t know how it can be saved if stuck open.

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Jess,
Thank you for posting your findings.

I have experienced failures of several brand new parts, OEM and aftermarket ones, right out of the box. I now view all new parts skeptically and test them if possible prior to installation. I have learned that “new” doesn’t necessarily mean “good”. Several other members have also posted about failures of brand new parts on this list.

Paul

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Isn’t the common problem that they are stuck closed? This one was evidently stuck open.

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Indeed, Paul - ‘new’ is not a guarantee of function, it has lead many a good man up the garden path…

Frank
xj6 85 Sov Europe (UK/NZ)

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Yes - but sometimes… maybe.

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Kirby,
I had 2 or 3 Cold Start Injectors (CSI) from my Series III XJ6 parts cars or spare engines that failed and did not spray fluid when tested. In 21 years I never had a CSI fail that was stuck open. I tried to get the CSIs that were stuck closed to work again by soaking them in fuel injector cleaner and Kroil for weeks, tapping them with a hammer, and applying 12VDC to the connector pins, but none of that made any difference. I was never able to get a CSI that was stuck closed to work again.
I never had a CSI in either of our running SIII XJ6s fail. I owned one for 19 years, and the other for 14 years. It seemed to me that when used regularly the CSIs worked great. But when they sat unused for a long time in a parts car or spare engine, that is when they went bad.
I agree that it is odd that Jess had a new CSI fail in the open position. If that happened to me I would try to see if I could get it to work, but then I am a glutton for punishment.:wink:

Paul

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Did you actually check the resistance over the pins, Paul - a ‘break’ would mean the coil inside is burnt out…

Frank
xj6 85 Sov Europe (UK/NZ)