Hi All,

This is an old post but hoping someone has some newer info on us poor OBD1 proprietary systems.

I’d like to see if I can pull codes off the transmission and/or other ECU’s in the car. Just figured out a transmission limp home light issue that’s pickled me for a year - just hope I made it out of the pickle barrel. Turns out that the right front ABS sensor plug may have been causing my trans to limp home on a whim. Jiggling it around and pushing & pulling seems to have exercised that particular demon. Will fix it permanent in a short bit.

Point is, if I had a way to pull the transmission and ABS ECU codes I could have saved myself many new grey hairs.

I’m thinking…

They are all just mini computers with serial communicating plugs? Though my age might be showing on this a little bit, my first computer experiences included using punch cards, then Commodore 64’s with no hard drives and a massive 512 meg floppy drive.

I’m thinking one only needs to know the com protocols and what strings the ECU’s need to have in order to vomit out other strings that when properly assembled would actually emulate a PDU output. Lofty goals perhaps…

I know these small single board Arduino computers are really cheap, can be configured to pretty much anything you need to control, and can communicate serially with pretty much any profile.

if anyone knows the baud rate, bits (probably 8), etc. and what commands were issued by the PDU to make the ECU’s chirp like a canary, and then what the return strings actually mean, I might be willing to give one of these builds a go.

or, does anyone know who manufactured the ECU’s and any make / model info for the ECU’s themselves?

tanks! And hoping someone out there is as esoteric as I am.

Dean

 

I have also a rough idle issue, how did check if the intake manifold gasket is ok?

Thanks in advance!

 

Good question. I couldn’t detect it in my driveway with the cigar test, but one of three shops was able to detect it. Not sure how they did it, but it resolved a very curious symptom of an RPM drop every 32 seconds, once warm.

 

Great, thanks for the info. I sprayed brake booster around the inlet but no reaction from the engine. My bank 2 is over fueling when idle and I suspect the Fuel Pressure regulator. Maybe it is failed and sucks up fuel into the inlet manifold via the vacuum hose.....will try to replace it and see what happens

 

If it’s just Bank 2, then everything leading into the engine is probably fine.

I’d suspect oxygen sensors first, then coils, then injectors.

It has to be something that can uniquely affect only one bank. Everything leading into the engine affects both banks, so when was the last time you replaced the oxygen sensors?

 

I did replaced all 4 oxygen sensors, all injectors with gaskets and new spark plugs. Also repaired the exhaust manifold and replaced Ecu.

so I’m a little lost why the car stays rough on idle. It drives perfect. Idles at 700 rpm but hole car is shaking and have a difference on short term fuel trim. That’s why I think about the vacuum of the fuel pressure regulator.




Stft on idle

Stft at 1500 rpm

 

What are your Long Term Fuel Trims?

If you pull the hose off the fuel pressure regulator and see any kind of moisture or fuel smell, then that would be it. If it’s dry and odor free,its probably fine.

There are not a lot of sensors that would only affect one bank.

Swapping coils around (and documenting which went where) could yield results.

 

Hi Vee,

My long term fuel trims are 49,22% on both banks. Swapping coils makes no different in idle.

 

Hi, at the risk of stating what in the UK we would say the ‘bleeding obvious ‘ , have you done a compression test? Sounds like all the hallmarks of an old school burnt valve.

 

Yes i did the compression test, all cylinders perfect the same

 

Bobgee,

Why did you replace the ecu? What was wrong with the old one? Has the car ever run correctly with the new ecu? Has the ecu been configured properly or is it just a used replacement with the exact same part number?

Paul

 

Sounds like you have covered all the normal possibilities,I would just check the wiring loom as they do become very brittle with age and heat. I had a similar situation with a 3.2 AJ16 and it turned out to be an ECU problem , urgh!

 

Just seen ptjs1’ reply, and have to admit to not reading your initial post fully re changing the ECU , my apologies blame the hot weather here in France! I gather we are talking about a European car, as I understand the late AJ16 cars run a programmable ECU and in the event of a replacement being fitted it would need to be configured up on the Jaguar WDS system , which nobody seems to have any more! Unfortunately this is becoming an issue with x300 owners with otherwise healthy engines.
As ptjs1 asked, why was the original ecu changed?

 

Water inside old one, repaired with new connectors but I thought maybe it’s not 100%. New one not configured and another Ecu from x300. How can I configure the ecu?

 

Hi, you might have more luck asking on the x300 site if anybody knows of a Jaguar specialist with the early diagnostic equipment . From memory the x300 ecu was a different part number to the xjs. .Have you tried the original ecu back on the car? I would also get hold of a wiring diagram and check the continuity from the coil pack and injector wiring back to the ecu connections , these wires are very thin and now getting old! Again good luck.

 

Bobgee,

As I'm sure you'll have found out, water in the ecu often manifests itself in corroded pins on the ecu and corrosion in the input wires on the plug. I would carefully check continuity back on every plug wire back to it's source / sensor, particularly the CTS and O2 sensor inputs.

Good luck

Paul

 

I will try that, thanks!

 

If your Long Term Fuel Trims match, then your short term trims are nothing to be concerned about.

Rough idling can be a host of items including:
1. vacuum leaks. I believe you said you've checked for these and have come up with nothing? You must check everything downstream of the MAF.
2. failing spark plug seals, Oil in the cylinders wreak havoc on an idling engine.
3. failing coils. Often times they bench test fine, but that doesn't mean they are working well. Are they original to the car?
4. oxygen sensors. You said you replaced them.
5. Idle Air Control Valve. Be careful here, the 5.5mm bolts that holds this relatively inexpensive sensor in place are loctited in and tend to snap when trying to remove it.
6. Coolant Temperature Sensor. Cheap and easy to replace.
7. I've never heard of one causing a problem, but the Air Temp Sensor, also easy and cheap to replace could be a problem?
8. EGR Valve. Has that been replaced? (If it's an EU car, then you probably don't have this. Did the car you pulled the replacement ECU come from an XJS with an EGR Valve?)
9. Throttle Body. You said it's clean. The butterfly should be at .002" when closed.
10. When all else fails, reset the TPS....only problem is that you need a WDS/PDU to do it. Dealer will charge you at least one hour labor, maybe more, and there's no guarantee it will work.

I'd start at #5.

 

Hi Vee,

1. vacuum leaks. I believe you said you've checked for these and have come up with nothing? You must check everything downstream of the MAF.
I check that again, maybe a new inlet gasket?

2. failing spark plug seals, Oil in the cylinders wreak havoc on an idling engine.
Is all clean, no oil at the spark plugs and new gasket

3. failing coils. Often times they bench test fine, but that doesn't mean they are working well. Are they original to the car?
Are original coils, did try to swap with 2 new ones in all cilinders but makes no difference at all, spark is good at all cylinders. Also engine runs perfect when driving

4. oxygen sensors. You said you replaced them.
Replaced all 4

5. Idle Air Control Valve. Be careful here, the 5.5mm bolts that holds this relatively inexpensive sensor in place are loctited in and tend to snap when trying to remove it.
Replaced with new one

6. Coolant Temperature Sensor. Cheap and easy to replace.
Replaced with new one

7. I've never heard of one causing a problem, but the Air Temp Sensor, also easy and cheap to replace could be a problem?
That's new to me, Do you know the location?

8. EGR Valve. Has that been replaced? (If it's an EU car, then you probably don't have this. Did the car you pulled the replacement ECU come from an XJS with an EGR Valve?)
Original EGR, ECU not sure if it has a EGR valve

9. Throttle Body. You said it's clean. The butterfly should be at .002" when closed.
Cleaned and Checked butterfly opening space.

10. When all else fails, reset the TPS....only problem is that you need a WDS/PDU to do it. Dealer will charge you at least one hour labor, maybe more, and there's no guarantee it will work.
Did the TPS test, was working perfect is SDD

I have ordered a new crankshaft sensor and hope that will help

 

Thank you for the excellent responses! So the only item on my list could be the EGR....that could make sense here.

I thought you had replaced the crankshaft sensor! Definitely a great idea. You are almost completely through the list. I would have added MAF, but you would probably get bad results while driving as well as idling so I didn't think to add that on.

The Air Temp Sensor is mounted to that 90 plastic elbow between the MAF and the Throttle Body.

While you're checking, pull off the small hose at the fuel pressure regulator and make sure it's dry and doesn't smell of fuel, If its dry and clean, it's most likely fine.