My 1985 V12 recently developed a cold running problem. Bogging down, coughing, and low power when cold and continuing until the engine was almost fully warmed up.

Checking the Coolant Temp Sensor revealed that readings were a full 30-35% low throughout the entire temp range although this is partially explained by the info that follows. Anyhow..... Replacing the sensor ($18 and 15 minutes) solved the problem entirely. Engine now runs great when cold. All fixes should be this easy.

I used a NAPA sensor, part number TS5520.

Researching the part number was a bit interesting...at first. I only got a few inches into a rabbit hole before realizing the myriad of substitutions and sometime conflicting information was gonna make for a very long night and not as much fun as I thought it might be. But I got as far as this:

What I took out of the car was a Bosch 0 280 130 055. Near as I can tell this is a Jaguar DAC4737....which is the coolant temp sensor for the Marelli ECU, not the Fuel injection ECU.

What should have been there is a Bosch 0 280 130 023....which is Jaguar DBC3728 or EAC3927 and used on a wide variety of models.

NAPA uses the TS5520 to replace both the “023” and “055” Bosch numbers....and calls it an Air Temperature Sensor....which it isn't!

However, using Jaguar part numbers the EAC3927 and DBC3728 I discovered they are both serviced by NAPA TS5597.

I also discovered that Bosch-023, NAPA TS5597, EAC3927, and DBC3728 are all serviced by Standard Motor Parts TX107.

The DAC4737, NAPA TS5520, and Bosch-055 are serviced by Standard Motors Parts TX18.

As it turns out the resistance specs for the Marelli sensor and the Fuel Injection sensor are very similar:

TEMP Marelli Fuel Injection
10C 4.4k ohm 5.9k ohm

20 2.5k 2.5k

30 1.6k 1.7k

40 1.2k 1.2k

50 840 840

60 630 630

70 470 435

80 210 325


Cheers
DD

 

Very Interesting ! I really don't know what's in my 91 5.3 or don't have any of the related issues, I know I have replaced it at some point along the line. Just wonder how long their life is. In any case at $18 it's probably good idea to add the NAPA # TS5520 to the xj-s inventory. Thanks very much for all the time related research .
Larry

 

I don't think there's a typical, predictable life span. Failures are common, though. And the price and ease of replacement makes them non-hateful if guesswork is involved.

Actually, I'd buy the TS5597 if I was doing it again. That's the technically correct replacement. The 5520 is simply close enough to work.

Cheers
DD

 

Interesting symptoms, my car does something sort of similar when cold and I haven't been able to look at it. Acts more like a "choke" issue though, where it will bog when dead cold if revved lightly. For the first 1/2 mile or so I have to give it more gas to prevent bogging but it isn't slow and doesn't cough during this time. Had assumed it had something to do with the AAV but I have two coolant sensors lying around, so maybe I should stick one in just to see what it does.

 

Worth a try.

Near as I can see the AAV really shouldn't have any bearing on cold driving problems. It's only there to provide a higher idle when cold. Once the throttles are open to accelerate I can't see how the AAV would influence anything.

Cheers
DD

 

So ECU temp sensor is driver-side and fuel is passenger side? (on a US car) I have to wonder why there are 3+ temp sensors on the car for everything gauge included...ohwell typical Jaguar design features.

My car sputters and has questionable idle in park while cold, now that summer is ending and its 10c in the morning but will fly like a spitfire when in drive/warm given that everything else is new I only have the passenger side coolant rail sensor that is old, I believe Doug clarified in a post awhile ago that it was infact the marelli sensor on that side, when I posted a picture, ahead of the cluster gauge single prong sensor.

Maybe I'll replace that and see.

 

I'm pretty sure everything is run off the LH sensor. The RH sensor is just for the gauge

 

Probably depends on the car. I seem to have two socket type sensors and one cluster gauge single prong on this marelli car. The Jaguarclassicparts diagam shows it but doesn't say which does what.

 

If you have Marelli ignition then you'll have three: one for the F.I. ECU (LH water rail) , one for the Marelli ECU (RH water rail) , and the single wire sender/sender for the dashboard gauge (RH water rail). If you have Lucas ignition you obviously won't have the third CTS that the Marelli cars have

I'm not sure enough to carve this in granite but I think all the original Bosch CTSs for the Marelli ECU were green top.

Cheers
DD

 

Its green your right. I've had bad luck with aftermarket sensors like the cluster gauge sensors before so I'm hesitant to replace this one even though your car issue sounds exactly like mine although more severe.

 

There is a good reason that older cars have multiple sensors.

New cars the temp sensor is connected to the ECU and CANBUS info is sent to all other systems.

Older cars (pre CANBUS) if you connect multiple ECU's to a single sensor one ECU can load the sensor causing inaccurate readings for the other electronics, this is why our cars have multiple temperature senders.

 

I spoke a bit too soon. I'm in the midst of a mystery.

The car behaved beautifully for a few days and then the cold driveability problem returned.

- New sensor checked and operating according to spec
- Tried the TS5597 sensor just for the heck of it. No change.
- Checked old sensor and, yup, it's well out-of-spec
- Checked TPS. Correctly set, smooth voltage transition.
- Replaced connector. No change; I didn't actually see anything wrong with the old one to be honest.

After replacing the connector there was no change. Very poor cold running behavior as described in my first post. After a couple days, though, the problem as disappeared and the car runs well when cold. As before, the engine runs grrrrreat when warmed-up. It's everything a V12 oughta be.

I think the fiddle-factor is a play here. I'll wait for further developments but my gut tells me a subtle wiring fault is afoot.

Cheers
DD

 

I've been meaning to update this thread....although what follows isn't very informative.

I inadvertently solved most of the problem with an Italian tune-up....which V12s always seem to benefit from and mine was overdue for. Big improvement in cold running.

But......

There's still a hesitation that shouldn't be there....and wasn't there originally. It's subtle enough that I might be looking for a needle in the haystack.

Cheers
DD

 

Could it be something in the vacuum / ignition system? Vac advance not working correctly? I assume you have checked that the advance is actually advancing? I once bought a brand new advance mechanism, and the lever arm was completely bound solid out of the box. I ended up cleaning the lubricating the old one and putting it back.

 

 

Worth checking, thanks

I checked the advance systems...vacuum and centrifugal.... a couple years ago before installing the engine....but that was then and this is now.

Cheers
DD

 

Ah, good point.

In my mind I've been thinking a of a lean spot in the fueling. But the 'bog' of a bit too much fuel can feel just like the 'hesitation' of too little fuel

Cheers
DD

 

I one had a dump valve go intermittent on me, easy to recognize as with the trip computer on instant fuel economy when the dump valve dumped the vacuum there was no advance and the fuel economy dropped about 25%. The instant fuel economy feature is actually quite a useful diagnostic device, when you know what it should read under normal conditions.

 

Good catch on the dump valve!

Back in the days when I had a working TC I, too, found it useful as a system monitor of sorts.

As it stands, though, I have a small collection of non-working TCs. Sooner or later they expire, it seems. As 1980s-vintage gizmos go, they probably held up better than most. I have one on my desk as I type. One of these days, if the mood strikes, I'll open it up and perhaps see some cracked solder joints or other easy fix.

Anyhow, no dump valve on mine. I've bypassed all the vacuum advance controls.

Cheers
DD

 

Still havn't resolved the issue? have you tried double checking the O2 sensors and the ground wires for them? It occurred to me that your issue sounds similar to mine while I was checking this thread post yesterday, my O2 sensors weren't sending a signal properly and thus the car defaulted to whatever it thought was going on instead of using feedback from the sensors - resulting in a bogging down effect at takeoff, among other issues. Anyways thanks for all the cross-reference numbers on the temp sensors I bought and fitted a napa sensor yesterday and removed the corroded and discolored 30-year old original. Car starts and runs better now.