87 Series III XJ6 Rough Running

[Michael J.]

I started having trouble when starting the car as if the cold start injector or one of the injectors was sticking. Car seemed to run on 4 or 5 cylinders, belching black smoke.

I pulled the injectors and rail and ran injector cleaner through each and tested for spray pattern and shutoff. All seem to be ok. Checked the cold start injector ands it also seemed to me ok.

With some coaxing, if I get the RPM to 2000-2500, the engine runs smooth. I thought it might be a vacuum advance problem or bad spark plug. I replaced the plugs. I disconnected the advance vacuum line at the throttle body, pulled the cap (no sign of cracks or carbon tracking). I used a hand held vacuum bleeder pump and confirmed that the vacuum advance turned.

I had a spare air meeter and swapped it as well.

After each repair, the problem remains the same. I have about 1/3 tank of premium fuel on both sides.

With the car running, and using mechanics stethescope, all six injectors are clicking.

Any thoughts? How do I check the Power Resister for proper function?

 

[Deleted member 8987]

I haven't worked on one of those in 20 years.
Memory is foggy.
But:

I would fathom a guess that if the car is belching black, it isn't ignition.
Ignition is firing enough to try to overcome an extremely rich condition.

I would remove the air filter first.
Then I would unplug the electrical to the cold start injector.

Then I would ask myself a couple of questions:

How old is the gas, did I just put some in, and when did I last change out the fuel filters?

I have seen all sorts of odd behavior with plugged filters, where the computer tries to feed more gas than it needs due to low pressure, but not necessarily on an XJ.

Injectors checked out, and are clicking, the other things are:
Does this one use a MAP sensor for manifold pressure?
If it's toast, it tells the computer (or can) that you are wide-open throttle and dumps fuel accordingly.

Baro sensor not so much.

The 2K RPM would tell me you are way too rich, and 2K is the amount of fuel it's feeding it.

 

[Exotexs]

Black smoke is associated with an over rich mixture;

the symptom points to the Cold Temperature Sensor (CTS) in the Series 3 XJ-6, a classic symptom of a bad CTS. Check ebay for a cheap replacement.

Ex

 

[Deleted member 8987]

I can't remember....does the temp sensor control all the injectors or just the cold start?
I remember just unplugging the cold start injector electrical connector to "prove" the issue.

 

[Exotexs]

if you're asking me, heck I don't know, all I know is that the CTS is a known issue with rough idling when cold, AFTER the engine has started. The Cold Start Injector (CSI) only runs for a few seconds then it is out of the picture. Obviously the CSI receives a signal from the CTS telling it "this engine is cold, you must go to work NOW".

And by the way, it is not "Cold Temperature Sensor", but "COOLANT Temperature Sensor". My apologies.

Ex

 

[DrEntropy]

I'm in the same camp... tho poor recollection as its been years, but:

Head temp sensor is the FIRST thing to suspect. There's also a chance the pressure regulator on the rail has taken a dump (literally).

 

[jessebogan]

The coolant sensor is a long time failure part. The original is brass w/ plastic where the connector goes. The current modern replacement is black plastic. These seem to be much better. Check the wires in the connector also. The cold start injector is controlled by the thermo time switch. Should only run the briefest of times when the outside temp is hot. Measure the fuel pressure at the hose connection near the battery. Plumb a guage inline there. Should be around 35PSI I think. If the regulator fails, you can see over 100PSI.

 

[DrEntropy]

ISTR 28~32 PSI but point is moot if it exceeds 35 for sure.

 

[Deleted member 8987]

Hmm.
I think some gray cells are firing a bit.

Isn't there a vacuum hose from manifold to regulator?

Is it on?

If not, pull it off, get someone to turn the key to get the fuel pump to run, if gasoline squirts out of the hose, the regulator is ruptured, and you are dumping full fuel flow and pressure into the intake.

 

[DrEntropy]

:thumbsup:

 

[Michael J.]

Swapped the Temperature switch, but it did not resolve the problem.

Swapped the Thermotime Switch since it regulates the Cold Start Injector circuit. It did not resolve the problem.

Filled up both tanks, was running on a 1/4 tank when the problem started this time. Does not appear to be a fuel quality issue.

I pulled the distributor cap for a close inspection under bright light. I have a crack near one of the clips that holds the cap on. I swapped the cap.

Did you know that the Owner handbook, the Maintenance handbook and the Service Manual do not appear to discuss which position on the cap is for which plug wire? No underhood decal either.

Soooo... Which plug on the XK engine is number 1?

Which receptical on the cap is for #1 plug wire?

What is the firing order? and do I insert the wires clockwise or counterclockwise?

 

[Deleted member 8987]

What you DO is remove the old cap, leave every wire in place.
INSTALL the new cap, hold the old cap in the same orientation as the now installed new cap (line up the clips) and transfer one wire at a time.

#1 is at the rear, at least on older Jags.
You will have to pull #1 plugs and find the compression stroke to see where the rotor points.

 

[Exotexs]

here's an illustrated page which should help you follow each wire.

https://autorepair.about.com/library/firing_orders/bl-fo-12620.htm

Ex

 

[jessebogan]

It is pretty easy to crank the engine over by yourself to find out where #1 is. Remove the spark plug closest to the windshield. Look on the firewall near the battery. You will find a rectangular metal box with wires o plenty attached to the bottom. This is the starter relay. Look at the wires. On the forward corner nearest the battery there will be a white with red tracer wire. Look to see how it is connected, as there can be unused terminals on the solonoid near where it goes. Disconnect this wire, and put a paperclip in the terminal end. When you touch it to the battery positive post, the engine will crank. NOTE!!!!This bypasses ALL of the safety systems such as neutral safety switch. Make certain that the car is in P before you do this. Place a finger into(over) the hole left by the number 1 plug, and bump the engine over a little at a time until you get compression. It will be obvious. Stop there, see where the rotor points, and that will be number 1 on the cap. If you note which way the rotor turns, the rest will be simple. 1,5,3,6,2,4.

Have you checked the fuel pressure yet? Also, what kind of cap and rotor do you have? Aftermarket? New "lucas"? It might be worth looking on Ebay or emailing John AT noslucas.com and finding some old stock "real" lucas parts. In spite of all the jokes, I have found that the real english made stuff fits and works the best.

 

[Michael J.]

Well...

It is not the fuel regulator. No fuel coming out the vacuum port on the regulator.

The Wiring diagram of the distrubutor cap and plug wires was well worth printing out.

I wanted to take a second look at the injector spray patterns. I took the six nuts for the injector brackets loose and removed them. Removed the bolts from the rail supports at each end off. Removed the two Torx bolts for the cold start injector. Added 18" of 3/8" fuel injection line at the rear and 18" of 5/16" at the front. That allowed the fuel rail to be moved much higher so that each injector could be tested while still connected. I used a glass jar with a hole in the cap and with the ignition on, and a screw driver inserted into the airflow meter opening after removing the air filter, and a connector that I have a press switch and leads to connect to the battery,I tested the spray from each injector and was interested in whether each shut off. The rough running with black smoke does not seem to be injector related.

I acquired a used ECU. It did not solve the problem either. That leaves the "Power Resister" mounted behind the radiator below the air filter can that sends the signal to the injectors to open or close.

Anyone have any thoughts on how to test it?

 

[Michael J.]

I swapped out the power resister. Not that either.

Runs smooth at idle but starts breaking up at 1500 RPM.

Is there a good procedure for checking timing with a timing light at above idle speed?

If I put a Mighty Vac brake bleeder on the vacuum advance, with distributer cap off, it appears to offer smooth advance.

It is difficult to read the timing, best line of sight for the timing light id just to the right of the Air Pollution Pump, but the line of sight to be able to read the timing also seems to be the same spot.

I let it idle until normal temp to see if it only acts up cold.

It does it while hot as well.

 

[Michael J.]

Well, you are not going to believe what turned out to be the cause of the remaining symptoms.

The power steering pump was about to fail. I replaced the pump and the remaining running rich and rough stopped.

After having done all of the above, car would idle smooth, but start loading and breaking up as the engine was reved.

Could the bearings for the power steering pump starting to seize really have caused this? Why not at idle as well? At 2500 rpm did the engine now overcome the friction?

I am completely baffled as to why changing the power steering pump made the problem go away. I don't understand.