Evening All.

As the title suggests, I am working through some diagnostics and elimination process, thanks to the many previous posts on this engine issue. Thanks to all for the previous input, it has been most useful.

So, here is where I am at.

Full top end rebuild was done last winter, as cylinder 5 had no compression, back of the valve was so coked up it was not seating fully. All components cleaned, seats ground, and reinstalled. Compression tested and all cylinders are good. New Andy Stoddart CPS bracket, new CPS. Runs beautifully smooth in open loop, fires up immediately, then stumbles intermittently in closed loop.
New coils (although still on the list to confirm not arcing). New copper spark plugs. All grounds cleaned, plug connections checked, cleaned. ECU plugs clean, no water ingress. Injectors clean, good pattern and volume. Fuel pressure at 44psi.

On the highway I have had some rough running and sluggishness under acceleration, although intermittent. Last long run I had, the car ran like a dream, lots of power, smooth acceleration and motor purring... then I fiddled and fitted a new coolant temp sensor. Ran rough since, even after refitting the previous temp sensor. I am yet to jumper it out to rule it out as I have the fuel rail off for cleaning the injectors. Last visit under the hood I can see a very small nick in the sheath of one input to the coolant sensor.

TPS has been bench tested for smooth resistance, confirmed (as with anything, still a possibility, although the car has no 'dead' spot under acceleration or cruising)

O2 sensors are original and did not get removed during rebuild. (North American version, has 4 sensors and an EGR). I have removed the set from the other car, cleaned and ready for swapping and testing. Reluctant to purchase new until confirmed required.

As the ECU is a 95, I am not having any luck in getting live data, fuel trim etc. After checking compatibility of the ECU's from the Lawn Ornament, I was hoping I could read the motor info. I swapped over and fired up the motor, ran the same as before, little rough, although not unexpected as it would need to do a relearn. However I still have no access to live data, shows as 'not supported'. Apologies, I dont have the scanner info to hand, it is a JLR Specific, aftermarket reader.

I have a couple of other checks to do when I have the fuel rail reinstalled, any recommended checks will be added to my list.

Questions:
Is vehicle live data ECU based or Vehicle based? Wondering why the second ECU would read the 96/97 lawn ornament but not the 95.
Pictures attached are of the 2 ECU's. What PROM number should I check for to confirm the update? Silver one is the original 95 ECU. Black one has the 9333 PROM.
Is there a way to reprogram a 95 ECU to work with OBD2?
What other suggestions are there to cure the open loop misfire, without access to live data?

Thanks all. I have read through so many posts, my head was starting to swim and getting into overload.


From the Lawn Ornament. Had some water ingress, but working

Silver (top) original to the 95 running vehicle.

 

ECUs should be interchangeable from the 96 to the 95. I don’t know that for sure, but I’d love to find out.

The 95 ECUs do seem to have some quirks to it, specifically with the trims, but it should read like the 96. The PROMs should have nothing to do with that.

Have you tried reading it with something else? I use OBD Fusion app with a WiFi ELM27 dongle with my iPhone. I can read oxygen sensors and trims and so forth.

It is all pulled from the ECU.

Regarding the TPS, best way to check that is to use an analog multimeter. Digital can easily miss dead spots, analog shouldn’t miss it. You should be able to see needle twitches.

Not sure how many miles you have, but oxygen sensors are not meant to last forever. Just saying…

Ive had to replace my EGR in the past, although since it runs well when cold, I wouldn’t spotlight that just yet.

Lastly, the coolant temp sensor is a critical fueling sensor in both closed and open loop, so never underestimate its ability to throw a wrench in the AJ16 system. I’d fix that nick and make sure everything is optimal.

 

TSB has numbers for US federal cars. (maybe all North American cars?)

 

Thank you both for the input.

XREngineer was kind enough to verify that the ECU's are definitely interchangeable.

We have tried about 5 different code readers now, an ELM27 with Toad Scan, Fusion and OBD doctor apps. A mongoose JLR connection, We have downloaded IDS118 and 130, plus another JLR code reader as mentioned above. Every one will show throttle position and rpm, yet shows the trims and O2 as unsupported for the 95.

Im sitting at about 230000 kms.

I had searched for the TSB so thanks for the link, I just wanted to confirm the ECU is updated.

Most appreciated!

Fixing the nick on the CTS is next on the list, thanks for the notes on its wrench throwing ability! It has been on my mind ever since the swapping.

 

I just rolled past 150,000 miles on my car, so you're not too far away.

I would plan on replacing the oxygen sensors. They owe you nothing at this point. You have been playing with house money for a long time.

If you want to be frugal about it, the downstream sensors affect fueling, the upstream ones are simply there to make sure the downstream ones haven't failed. I would not rely on the OBD system to indicate oxygen sensor failure, clearly it had issues in 95. The 1996 is still notoriously stingy with issuing codes.