Ok long story really short.

3 weeks ago or so driving back after 120miles of highway driving and just as I was about to exit the Jag hesitated and acted like it was going to die. Pulled over checked connections and oil and whatnot (just shooting in the dark as there were no codes). After sitting for 10 minutes started up and no problems at all.

Fast forward to yesterday. It was 97* here and had driven 220 miles mostly highway. All of the sudden same hesitation except this time it threw up Check engine light so I pulled over. Checked VCM and Fuel Fail 44 was the code. Wouldn't start up after that but after sitting for about 30 minutes (waiting on tow) Just tried one more time and while rough it started and I could get home.

I have noticed since I bought it that some days it has a rough idle but performance has been consistent except these 2 instances.

Researching the Haynes there is a section about fuel filter and fuel pump issues saying it is a known problem when it is warm outside for it to have this problem.

My first thought however is TPS or O2 sensor because of the intermittent rough idle mixed with FF44.

Thoughts?

I really don't want to have to do the Fuel pump and Throttle body if I don't have to but if that seems to be the problem I will.

I guess the worst part is the Check engine and FF44 can be so many issues or combinations. What order would you check and what else could I check before I jump all over the place replacing parts like I did when the front end had the issues in a previous post?

Thanks in advance.

 

First thing to eliminate as a possible problem is the fuel filter. Super cheap maintenance item and a 20 minute job - however that probably isn't causing your FF44 issue - still, if you haven't changed it in a while ....may as well!

Larry

 

Hi Rutty,

It's certainly possible that you have a fuel pressure problem, so replacing the filter as Larry suggests would be worthwhile as a matter of course. On our '93, the cause of DTC FF44 was the heated O2 sensor (HO2S), which was not swinging its voltage properly. In the Engine Management Diagnostic Manual there's a routine for diagnosing the cause of DTC FF44, including testing the HO2S with a volt-ohm meter. If you don't have that manual, send me your email address via private message and I'll send it to you - the file is too large to post to the forum.

Another thing that can trigger the FF44 is corrosion on the ground studs that are used by the Engine Control Module (ECM), the two on the intake manifold studs, and the one on the firewall behind the cylinder head. But in my experience, problems with the grounds trigger the fault codes but don't necessarily cause rough running, so my instinct is that you have another issue, but I would recommend cleaning those grounds anyway.

What I suspect may be happening is this: when you first start the engine, the Engine Control Module (ECM) ignores the HO2S to give the sensor time to heat up to operating temperature (about 600 degrees F). During this start-up delay, the ECM uses a special fueling map for open-loop operation.

When the ECM expects the HO2S to be at operating temp, it switches to closed-loop operation, in which it relies on the inputs from the O2S, MAFS, IATS and CTS to determine the proper air-fuel ratio (AFR). If the HO2S is not operating properly, the ECM will adjust the AFR incorrectly, leading to either a rich or lean mix and causing rough running and stalling. When you try to immediately re-start the engine, the ECM knows the HO2S is still at operating temp, so it applies closed-loop fueling and you continue to have the problem. But when you allow a cool-down period, the ECM reverts to its open-loop fuel map and the engine starts and runs better until it goes closed-loop again.

It would be worth cleaning the electrical connector for the HO2S with zero-residue contact cleaner spray to see if that resolves the issue, but if not, I would suspect it's time for a new HO2S (easy to confirm following the diagnostic routine).

Your original sensor is probably a Bosch, and you can look up the correct part for your car with the online Bosch parts finder:

https://www.boschautoparts.com/auto

With the Bosch part number, you can search for the best price. When I bought ours the best price was from an Amazon seller. Other sensor brands are available at lower prices, and you can compare them at sites like Rock Auto. Just be certain to get a sensor that already has the correct electrical connector installed. The Internet is full of stories of folks who have had problems using the "universal" style sensors that require you to install the appropriate connector yourself. The problems arise in part because the HO2S on an XJ40 uses the small spaces between electrical conductors in the wiring harness to draw in fresh air for comparison to the exhaust gasses. Over-crimping or soldering the electrical connector blocks those air passages, essentially ruining the new sensor.

Sorry if that is a whole lot more than you ever wanted to know! Below are links to photos showing how the HO2S is replaced on our '93. Your '92 will be very similar, but the electrical connector may be on the right side of the engine rather than on the left like ours. Just follow the wiring harness from the sensor itself and you'll find it.

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page

Cheers,

Don

 

Big ole thanks to Don B yet again. I got around to messing with the Jag yesterday and Today. I started with a fuel treatment and that helped the rough idle a bit. Then I went to go check on the O2 Sensor connector. While it wasn't "dirty" there was some oxidation on the copper connectors. Cleaned them off and then a little fuse save and she is purring like a kitten again. I wen't ahead and got a replacement o2 sensor just to be safe but I think we are good.