Jaguar Repair: 87 XJ6 Start fine, dies in gear (part 2), distributer cap, back fire

Question
QUESTION: Hi Howard,

I finally found time to work on my car again ('87 XJ6).  I have a friend with a parts car and I swapped out the MAF, fuel pump, all relays on back fire wall (fuel, cold start,) and the car is still running rough right after the idle kicks down from reaching operating temperature (about 1 minute after a cold start).  It dies or runs even worse when I put it in gear.

Voltage going to the pump is 12.5v until it is gear, then it drops to about 11.3v under the load.

I wiggled the dist wires. They seem fine.  I also switched tanks (tanks were not filled at same time).

Right now, my best lead on the problem is the fact that the car runs perfect until the throttle kicks down after warming up.  About 2sec. after that the engine starts running poorly.  
Could it be the coolant sensor not giving a correct reading?  My other theory was the coil, but I wouldn't think it would be related to the timing of the engine hitting operating temperature.

I have not opened up the distributer cap yet to check coil.  Last month I replaced the cap and rotor, though.

Also, does this car give diagnostic codes on the dash or is it too old?

Thank you again!
Dave

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>>I have an 87 XJ6-probably about 150Kmiles- that starts, idles and drives fine for about a minute, then the engine will stammer and die in gear.

I got about a half mile from home the other morning when this first started. I was going about 40mph when it sounded like my engine died.  I coasted to the side of the road.  Re-started it...it sounded fine.  I put it in gear and it quickly died.

If the engine is warm/hot it barely moves the car in gear or sputters to a stop. It seems to idle and rev fine in Park or Neutral.

I had my son put it in gear while I pushed in on the MAF valve with a screwdriver and the car started moving again.  I'm assuming I've got a bad sensor somewhere.  I cleaned the MAF, but it didn't help.
Any ideas where to look next?

(I know my fuel filter & pump, cap/rotor, plugs and wires are all good... and fairly new. ) I haven't checked the coil.  My next thought was to take off the throttle body and clean the TPS.  Good idea?

Thank you very much in advance!
Dave<<

>>>Answer
Hi Dave,
This car has the Bosch "L" jetronic injection system and there are some tests that need to be done before you can condemn any part. Fuel pressure is critical so you need to know what the fuel pressure is at the time of failure. It needs to be about 32 PSI and when you apply a heavy load it needs to go to about 42 PSI. Did you try switching tanks when this problem started?
Your problem does sound like a fuel problem. The throttle position switch is just a full throttle switch and not in play with your problem. Even though a air flow meter can fail like that it usually stays failed and does not come and go. When you opened the door in the air flow meter you triggered the fuel pump but you still don't know what the pressure is.
The ignition can go until it heats up and get weak so you can test it with a timing light when it is failing. The module is a GM unit inside the box on the front of the intake manifold. The pick-up in the distributor is just a coil type and can be checked with an ohm meter. Air gap is about .015". When the engine is running wiggle the wires from the distributor to the module as they often break that lead.
Howard<<<


ANSWER: Hi Dave,
No code system on this car. But you need to quit throwing parts at it until you test to see what is wrong. If it runs ok on Aux air valve (fast idle system) and cold but will not idle and runs poorly after warm up you need to do some testing.
FUEL PRESSURE after warm up ???? 32# and 42 with vacuum off of reg.
Injection coolant sensor is about 1 K ohms cold and about 100 ohm at operating temp. Those are just rough figures.
Did you try adjusting the fuel mixture or idle speed when warmed up???
Timing needs to be set to factory specs and left alone. NO alterations to timing should be made to try to make an engine run better unless the engine has been modified.
Did you run a compression test on this engine?

Howard

---------- FOLLOW-UP ----------

QUESTION: Thanks again for your help, Howard.

Fuel pressure (when car is at operating temp and acting up) is 30# and 39#-40# with the vacuum off of regulator.  It also shoots up to 40# when the car is put in gear (which engine then dies).

My compression readings are:
6=139 dry/200 wet
5=152/180
4=140/195
3=140/190
2=140/182
1=140/170
(I think I got carried away with the wet test and put in too much oil -about 2 tablespoons instead of a teaspoon! I want to do that test again, but thought I'd tell you what I had for now.)

Coolant sensor tests fine.

I did not adjust the timing.  I meant that I didn't think the coil would get hot/fail the second the idle kicked down after warming up.  Maybe I'm wrong, though.

I unplugged the throttle position switch and it made no difference in how the car was acting (but you said that it only kicked in at full throttle, so that would make sense).

I'm just about out of ideas. I do know that the engine has to be cold to the touch before it will run fine. As soon as it warms up I have problems.

Any more help you can give would be appreciated.

Dave



ANSWER: Dave, the only other things I can think to look at is manifold vacuum and if you have a bore scope available remove an injector and the sleeve it sits in and insert a bore scope to see if the intake valves are heavily coked up with carbon. Also remove one of the caps on the exhaust manifold and test exhaust back pressure. It should not be over 1.5 PSI reving up.
Check O 2 sensor out put. (warmed up) and let me know.
Howard

---------- FOLLOW-UP ----------

QUESTION: Hi Howard,

I don't have a scope or a way to check the O2 output (at least not yet).

However, when I did the compression check I noticed my spark plugs were covered in carbon.  #1 was even a bit wet.
So today I thought I'd check out my throttle valve assembly and removed it for a good cleaning (it was covered with wet gunk).  Well, to my surprise I found about 1/2 inch of used, black motor oil sitting in the bottom of the intake manifold!

My first thought was a head gasket or valve problem, but the compression check didn't indicate that.  Where could the oil come from?  And most importantly, could this be the smoking gun for my idling/stalling under load problem?

Hope I'm making progress,
Dave

Answer
A regular volt meter can check O 2 out put.(blue wire) .5 volts = normal and a lean voltage = a lean mixture and a rich voltage (1v.) = a rich mixture. (other two wires (black - white w/green tracer)are just a heater)

Oil can get in by the breather pipe to the front of the head. Your wet compression test did not tell you if you have a ring problem or not which could put a lot of oil vapor into the vent and intake. You should remove the cover on the front of the head and clean the fine screen.

Don't leave so many stones unturned (timing and now wet test and O-2 output) also clean and gap the plugs now that you know they are not good.

let me know,
Howard