Check engine lite came on my 92 XJ6. Shows FF 39. What I can see is something to do with the EGR valve. Where is it and how hard to get to? Been told it might only need cleaned out. Any advice on inexpensive fix??

 

Hi beegee,

FF39 or Fuel Fault 39 indicates "EGR Circuit Faulty System Operation." See the chart below from the Haynes XJ40 Repair Manual, which you can download from this forum:


The EGR valve is a squat cylindrical device mounted on the top of the exhaust manifold on the right side of the engine (as viewed from the driver's seat). It is made of metal and often has a gold-color anti-corrosion plating (maybe cadmium or zinc/chromate).

Some of the possible causes of EGR system malfunctions are a failed EGR valve or carbon accumulation in the valve and/or the EGR pipe and the port mounted on the underside of the intake manifold behind the throttle body. Failure of the EGR vacuum solenoid is rare, and should trigger FF37 instead of FF39.

You can test the EGR valve diaphragm for free movement by reaching into the recesses on the underside of the valve body with your fingers and pressing upward. Do this only when the engine is cold - when the engine is running, the EGR valve and exhaust manifold are hot enough to burn you. If you have a vacuum pump, you can disconnect the vacuum hose from the EGR valve and attach a hose to your pump and apply vacuum to the valve. I believe the diaphragm should open with about 20 in. Hg. / 68 kPa / 10 psi of vacuum but try higher vacuum if necessary. My hand-held MityVac pump can pull close to 30 in. Hg. of vacuum. EGR valve failure is common at higher mileages.

Another common problem is carbon build-up in the EGR port on the underside of the intake manifold. The photo album at the link below shows how to clean it. Unfortunately the large images are currently down at the Jag-Lovers forum, but you can see my thumbnails and descriptions:

XJ40 Throttle Body & EGR Port Cleaning

One other maintenance item: whenever I have an engine management system (EMS) related fault code, I take the time to clean the ground points referenced by the engine control module (ECM). There are two on the intake manifold and one on the firewall/bulkhead behind the cylinder head. Sometimes cleaning these grounds will cure a fault code. Here are some photo albums on cleaning the grounds and one on the battery power connections:

Grounds-Earths; Master Diagram
Grounds-Earths: Periodic Maintenance
Grounds-Earths: Engine Compartment
Grounds-Earths: Interior Cabin
Grounds-Earths: Trunk / Boot
Battery Power Connections: Firewall / Bulkhead-Starter-Alternator

Cheers,

Don

 

My XJ6 has only 65000 actual miles on it. All though it be 25 yrs old. Have to buy a Haynes manual. What is the best way to reset the check engine lite? Last time I discounted battery for a few minutes. Than none of my dash board idiot lites came on nor did my gauges come up. I pulled fuses (not broke) and re inserted. everything came back to life.

 

For all the info about DTCs for the 4.0 AJ6 please read the S91_AJ6 4.0 Engine Management.pdf.

I uploaded it to this site and Gus has it also.

It is over 13mb so it is too large to attach to this post!!!!

bob

 

It goes without saying that the best way to reset the CEL is to fix the malfunction that triggered the warning. But there are ways to temporarily clear the CEL, including disconnecting the battery for a couple of minutes. On our '93, after reading a DTC on the VCM, with the key still in position II (ON), I can pull the fuse for the Instrument Cluster and watch for the speedometer and tachometer needles to drop below zero, then reinsert the fuse before turning the key OFF. I'm not sure if this same procedure applies to a '92, but it's worth a try.

Cheers,

Don

 

Don B has it correct.
Open the center console lid (fuse box 3) and remove the fuse (5 amp) for the INST PK (Key On Engine Off) and wait for the speedo/tach needles to 'drop'.

Reinsert fuse and the code is cleared.

bob

 

beegee,

The document that Bob mentions is a treasure-trove of information on the engine management system with troubleshooting flow-charts for diagnosing all the trouble codes, and I was remiss in not mentioning it myself. Thanks to Bob's time and effort to upload it to the forum, you can download it here:

S91 AJ6 4.0L Engine Management System / OBDI Diagnostic Guide

See pdf pages 106/107 for information on the EGR system and troubleshooting FF39.

Cheers,

Don