It only does it upon cold start. When it is warm, it runs perfectly. No issue with the tensioners or timing. If it was the timing, it would always be doing it... So no worry about them

 

I'll see if I can get it on video tomorrow.

The colder it is outside, the worse it is. If the outside temperature is high (like +35°C), the problem is barely there. At the moment, around 0°C (freezing for those who can't do centigrade/celsius), it is hard to keep the car moving.

Very hard to explain...

 

Hi Damien,

The X308/AJ26 schematics don't make it clear whether the Instrument Cluster gets its coolant temperature signal from the ECTS or from the Heater Matrix Temperature Sensor (HMTS) by way of the Air Conditioning Control Module (ACCM). The schematics show the ACCM receives a signal from the HMTS and shares an engine coolant temperature signal with the IC. The ECM receives its coolant temp signal directly from the ECTS, but the schematics do not show that the ECM shares an engine coolant temp signal with either the IC or ACCM. On our XJ40 there is a separate sender for the Instrument Cluster temperature gauge, but I don't see one for the X308. So all of that to say, I'm not sure of the answer to your question.

If the IC receives its temp signal from the HMTS via the ACCM, then the dash gauge would be independent of the ECTS.

If the wiring harness for the ECTS is shorted, replacing the sensor would not correct the malfunction.

If you have a scanner capable of reading live data, you may be able to watch the coolant temperature signal the ECM is receiving.

Cheers,

Don

 

On a x308, the gauge get its signal direct from the temp sensor.
If the sensor fails, the reading goes to a default of sixty-some degrees for ecu purpose, and the gauge in the cluster reads accordingly (as far as you read any temp on it at all).

 

Okay, got a video done today... Caught it all really well.


If you watch it, the engine starts perfectly. Runs really well. Around 45 seconds into the clip it starts to pop. When I stop at the end of the road, the engine has a very erratic idle (up down up down). When then pulling away, pedal FULLY pressed into the floor(!!!), the engine pops (as can be heard) and then gains more power. Once set on cruise at 60 kph the engine behaves like new. At the end I pull into another road and the engine accelerates as a normal car.

IF it had jumped a tooth, it would always pop and bang. And it doesn't. ONLY when the car has stood a while and is TOTALLY cold. If the gauge moves a tad, it will run like normal. It does this ONLY on petrol (gas doesn't kick in for a while). The plugs are barely worn (just around 15k km). The timing is spot on. No nasty noises upon start up either than the popping. I can "delay" the popping by putting the tranny into "2" and locking it in 2nd. But as soon as I stop again it pops again.

 

Doesn't sound like timing related backfire. Sounds more like bad motor mounts. Have you done a recent compression check? Have you checked the torque on the plugs? I had a ticking sound on mine, after changing the plugs: turned out two of the plugs were loose.

Other than that bit of noise while cold, sounds superb.

 

Hi Eric,

I may be missing something, but in the 1999 XJ Electrical Guide, the schematic for the Instrument Pack, Figure 8.1, shows that the signal for the engine coolant temperature comes from the Air Conditioning Control Module (ACCM) and refers to Figure 7.1. The Instrument Cluster (IC) connects directly to the Coolant Level Switch, but no direct connection to the Engine Coolant Temperature Sensor (ECTS) is shown.

Turning back to the Climate Control schematic on Figure 7.1, a direct connection is shown between the ACCM and the Heater Matrix Temperature Sensor, but no connection is shown to the ECTS. The ACCM sends a coolant temperature signal to the IC. This is what makes me wonder if the IC temperature gauge gives a reading of the coolant temperature in the heater matrix and not in the engine bay.

Any clarification or reference would be appreciated.

Cheers,

Don

 

It's def. not the engine mounts... Or they would always make that sound. I had checked the plugs a long time ago but I can check again..

Got to be something there. I might just simply zip tie all the coils to their plugs and co...

 

Don,

Not questioning your research done, just talking from my experience.
Electronics can go in weird ways .
If you pull the connector, you will get a sixty something reading on your torque, the temp gauge half up, and the restricted perf. warning.
I got that after replacing the thermostat tower, and with a plastic piece in the connector preventing it from making contact.
Mine is a very early 1998 4L.

 

Hi Eric,

I'm always happy to learn something!

Are you saying that if you pull the connector on the ECTS the temperature gauge in the IC defaults to a static reading halfway between C and H even when the engine is cold?

I understand why you would have restricted performance since the ECM will trigger it for a variety of ECTS-related issues, including a disconnected sensor. ECTS-related DTCs that will trigger RP include P0116, P0117, P0118, P0125, P0171, P0172, P0174, P0175 and P1243.

If the IC temperature signal comes from the ECTS, perhaps it is via CAN between the ECM and IC. I just don't see any hardwire connection between the ECTS and IC. The schematics clearly show that the IC engine coolant temperature signal comes from the ACCM, and the only temperature sensor shown to be connected to the ACCM is the HMTS.

If I get the time I'll see if I can find the answer in the Engine Management Systems manual.

Cheers,

Don

 

Once the cars have CAN many signals are sent in network packets (cuts the wiring down). I expect ECT is one.

 

That seems like the only remaining possibility. I wish it were spelled out in the Engine Management Systems manual or Electrical Guide, but I haven't found the answer in either.

Cheers,

Don

 

Do you have any way to monitor STFT (short term fuel trim) on bank 1 and bank 2 while driving? If you can, this would help narrow the problem down to either a specific bank issue or if it's both banks acting up. In other words, I'm trying to see if a coil is acting up on one side or if there's a fuel trim issue with both banks.

 

In the 98 XJ Electrical Guide, wayy in the back, there's a very thorough listing of what signals are received/transmitted by module, with short explanations of each. See the Appendix, starting page 147 in the '98 MY Electrical guide available here http://www.jagrepair.com/images/Auto.../jagxj1998.pdf

Under the INST section (so, the instrument cluster) there is "CAN engine coolant temperature /// Engine coolant temperature in Celsius /// (source) ECM"
There's also charts further on for each type of data sent that show which modules send/receive that data.

So that comes from the ECM. Scrolling back to the electrical diagram for engine management, section 04.3 for part 1 to the AJ26 3.2L engine, only ECTS is seen there, no heater matrix sensor that I see. It does share a ground wire with a few other components, a couple TB related sensors, and maybe something else I didn't immediately see.

 

The STR has a similar breakdown of data (network packets etc) at the end of the elec guide and shows ECT as being sent around.

Normal for cars nowadays. The harnesses are huge but would be horrific without this.

 

Perfect! That answers the question! Thanks, nilanium!