2000 S-TYPE 3.0. Im going nuts with this one. Jag runs great with no problems except po code 430 for converter. When outside air temp is above 65 degrees no problems, however below 65 degrees it starts then stalls about 7 times then runs fine rest of day. This only happens below 65 degrees. Just tuned up plugs, etc and no vacume leaks found. Fuel pump checked out ok. I checked all threads but no luck. Had manifold off when did plugs and vacume hoses checked ok, even this little nasty elbow at rear under the manifold. I wonder if the MAP sensor or other fuel sensors etc. could cause this problem. By the way,again, after it starts it runs fine, ANY THOUGHTS, and as always, Thanks.

 

Certainly an odd one. Some quick thoughts:

1) When did the problem start? You mentioned some recent work. Did the problem start after that? Or was the work an attempt to fix the problem?

2) Will the engine behave above 65 degrees but act up on the same batch of fuel when the temp drops? I'm wondering if there could be some weird problem with fuel quality sold during colder weather. Kind of a long shot, but maybe the 65 number is a red herring. Perhaps the issue is winter grade fuel and the ambient temp starts dropping below 65 around the time gas stations switch from summer to winter blends.

3) Does the engine act up if warmed up but restarted on a cold day? Or does it only happen with a cold engine?

4) Have you tried switching fuel brands? Personally, I'm very partial to Chevron and use that almost exclusively. Fuel injected vehicles are fairly tolerant of fuel quality, so this may be a moot point. My old pickup and Jeep (carbureted), on the other hand, are VERY sensitive to fuel quality. I'd suggest switching your brand of fuel and see if there is any improvement. Won't cost anything to try but a little bit of time.

5) Ginger or MaryAnn?

 

When was fuel filter last changed? How was the fuel pump tested?

 

when it stalls, is it lean or rich?

 

MaryAnn!

 

Thanks for your thoughts. After engine starts no problems untill next morning if temp below 65 degrees. changed fuel with 3 companies using 92 octane, Fuel pump tested with pressure guage at output line from pump, and fuel filter changed when fuel pump tested. Not sure but seems to run lean when staling as no fuel smell. Problem started last winter here in south florida and had all work done last year. Had no problem again as temp stayed above 65 degrees. Couple weeks ago temp droped to 65 and problem noted again. Again, after jag starts ift runs great the rest of the day, then park overnight and next morning same problem. However if temp above 65 the next morning I have no problem. Had two mechanics work on with no luck. Jag dealer here is super expensive but may need to bite the bullet.By the way jag has only 85k miles and only po code is 430 for the cat.(is that drivers side cat converter?)

 

I'd go after the root cause of the P0430 code first.

 

What are the actual LTFTs? Engine hot, parked. At idle & then rev to about 2500.

Those 4 numbers will tell you if you might be chasing an air leak or definitely aren't.

Then if not start looking at other sensors (IAT, ECT, ...).

Er... who are Ginger & MaryAnn?

 

For our friends across the pond, the background of THE most important question of our time:

Ginger or Mary Ann? 'Gilligan' fans still ponder question - TODAY.com

 

I wondered about that, too, but am on the fence with this one. P0430 means the converter efficiency is below a certain threshold. In most cases, it just means the converter is old and tired. But since the converter is downstream of everything else, a fault by itself there shouldn't really have any effect upstream.

Caveat on codes P0420 and P0430 here, including some of the criteria for what trips these codes:

https://www.jaguarforums.com/forum/s...al-cat-143685/

I like JagV8's suggestion to check the fuel trims. If those check normal, it might be time to make a low-buck gamble on the upstream O2 sensors. Those are normal wear and tear parts, and they tend to drift out of calibration as they age. So much of the fuel scheduling is based on the O2 sensors, so it's generally worth the gamble.

The early model O2 sensors are quite inexpensive. I installed new Bosch sensors a while ago and they were only about $25 each. Stay away from off-brand universal fit models that require splicing the wires. Also, keep your existing downstream sensors for now, as explained in the link above.

The other part worth a gamble is the Intake Air Temperature (IAT) sensor. RockAuto had them for about $6. The IAT typically doesn't go bad without setting a code, but who knows. You might even try disconnecting the IAT and see what happens. You should get a new fault code for the loss of a sensor, but the computer should also revert to stored standard values so you wouldn't be stranded. If you see no change, the problem lies elsewhere. If the car behaves, it's not conclusive the IAT was at fault because the default programming may inadvertently compensate for another issue, but it's worth a shot.

Also, you mentioned the fuel pump was tested "with pressure guage at output line from pump". Are you talking about the injector rail on the engine, downstream of the filter and the fuel pressure regulator? This is a tee fitting and the reading can be done with the engine running. Or did you disconnect the line closer to the pump (obviously engine off) and take a reading upstream of the filter and regulator?

 

OBD can tell you what IAT etc read and usually you can eyeball the value and go "fine" or else "whoa, that's within range but wrong". In the latter case it can't flag a code but will fuel wrongly and the trims will be odd.

Thing is, if you swap parts but never got the trims you don't know if you've wasted money or what.

A P0430 can even be due to an exhaust leak or a bad O2 sensor that's "lazy". How many parts do you fancy swapping hoping to get lucky rather than taking some readings...

You do want fuel pressure as seen by the injectors (another OBD value if you feel inclined to look, but a gauge will do).

 

No, no, I'm agreeing with you 100%. Definitely read the fuel trims, etc., before doing anything.

I forgot you can read the IAT, so uff dah on me. As you said, you could see a value that is within normal range, so no code is generated, yet the value might be way off.

I never feel bad suggesting new O2 sensors, though. Unless one has access to an exhaust analyser, we mere mortals have no way of knowing if a sensor is accurate. By comparison, if you had a suspect IAT, you could compare it to the weather report. If your IAT reading shows 20 degrees and the weather report says 90, you'd know at least one of them is wrong. One could even factor in a lifetime of experience with weather and cast the tie-breaking vote.

Not so with O2 sensors, though. What's the ideal stoichiometric ratio, right around 14.7:1? Whatever the value, an early O2 sensor's switch point is calibrated for that. Let's say a sensor's switch point drifts off to 12:1 or 18:1. The onboard computer has no direct way to know. The switchpoint of an old, tired sensor would still put out a signal that would be misinterpreted as being good. The accuracy would have to be way off before the computer flags it as a fault. The only way to be positive about the accuracy would be to use an exhaust analyser. Unlike the IAT example, you'd have no easy (read: inexpensive) way to know if an O2 sensor is still accurate.

One indirect means is to watch the switching rate. As an O2 sensor ages, the switch rate slows down. If it gets too slow, it will get flagged. So observing the switch rate can kinda sorta work, but it's somewhat subjective. And this still can't confirm the accuracy of the switch point.

Please understand I'm as cheap as they come. Lazy, too. I don't like to do one lick of work more than necessary, nor waste a penny better not spent. I'm even reluctant spending other people's time and money. But since O2 sensors do drift and slow down as they age, I consider them normal wear and tear items. Just like spark plugs, fuel filters, etc.

It's kind of like the infamous battery thing with these cars. How many oddball faults have been fixed with a new battery, even if the old one tested fine? Usually a $150 battery is a good gamble for certain symptoms, versus taking the car to a shop and paying for a couple of hours' worth of diagnosis that may not find anything.

With the OP, if the fuel trims and other readings all check okay, I still say a pair of upstream sensors is worth a gamble. If that doesn't help, I'll still sleep well at night as they aren't expensive and don't last forever.

Ixnay on the IAT sensor, as I forgot you can read the value with a scanner.

Still waiting to hear back on the fuel pressure reading. Keep in mind there's no guarantee the sensor on the injector rail is accurate. You'd want to confirm it with a mechanical gauge at the rail test fitting. I'm not sure if that sensor is strictly for monitoring, or if it is part of the control system for the pump. Anybody know offhand?

JagV8, remember, I'm fully agreeing with you. I may be dumb, but I'm not stupid. When it comes to these cars, you da man. I'm just an apprentice dung eater offering what I think are cost-effective next steps if everything you suggested checks okay.

 

We're good - I wasn't even disagreeing with you either! Just trying to make sure some easy and cheap things were done (OBD tool).

With the 2002.5MY+ (2003+ USA) cars I think the O2s are more trustable because the upstreams are wideband aka linear. These let the PCM get the fuelling almost exact and then tweak it very slightly using the downstreams. If an upstream is getting bad the reading on the downstream should cause code flagging because it will say no O2 when the PCM knows it caused some or the reverse. (OP's car is not like that so I guess the PCM has less chance to figure which is OK or if not then how bad.)

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Point of interest (well, maybe!): the PCM periodically deliberately misfuels to test the O2s (esp. downstreams).

In any case, the PCM swings the residual O2 around a little so that the cat works as designed (they actually adsorb some O2 then release it when made to due to the exhaust gas mix).

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I think if sensors, wiring, computers, etc all cost nothing (and weighed nothing and so on) they'd fit more sensors so that the cause of codes could be flagged more accurately. E.g. it can now be tough to diagnose that there is an exhaust leak.

 

I see that Mary Ann has got 82% of the vote. This partially restores my faith in humanity and is similar to the age old Betty vs. Veronica conundrum where Betty leads at 80%.

 

Can't speak for anybody else, but these inner workings fascinate me. Alas, even with a sophisticated scanner, we can only poke around the edges of the programming. We can read up to some extent, but for the most part we have to make educated guesses about inputs and outputs, and how the PCM responds to abnormal situations.

I may be in the minority, but I'm a big fan of OBD II. When working on an older vehicle, it feels like I'm in the stone ages.

 

Scattered around the net are quite a lot of background documents such as the thinking behind why they (CARB, et al) chose the sensors and actuators, how various odd events can be diagnosed, and - well, there are a lot if you're interested. Also ones about potential future things.

 

Definitely.

 

+1 on the IAT. Common cold issue on the Ford 3.0. Can be cleaned with carb cleaner.