hi: i just checked the timing on my '87 xj6. the strobe light revealed 24 degrees. the engine was at normal temperature and the vacuum line at the distributor was disconnected and the probe was placed on plug wire #1 so i think i had it rigged up correctly. i know i have to back the timing down (retard?) to 17. i am curious what effect 24 degrees has on the engine? ren

 

ren,
Generally speaking, a little more initial/basic advance (vacuum disconnected) will make the engine idle a little faster, make the engine sound cleaner and maybe provide some small improvement in gas mileage (on the highway when the vacuum is hooked back up). Too much advance (with vacuum connected, in driving mode) may make the engine kick back on the starter (extreme advance), but most noticeable will be audible "ping" or "ignition rattle" when accelerating and using low octane pump gas (like we all do). Just a WAG on a stock engine with 7* more advance than spec...maybe nothing or just a little rattle during brisk acceleration. Don't dismiss that rattle if you hear any. That is the sound of the fuel detonating too far before Top Dead Center (TDC) and beating the pistons and bearings to death.

If I were you, I would leave it and just do a little drive testing. The factory set that spec with a large nod to emission controls back then. If you sense any of the conditions I've mentioned, you should probably set the timing back to stock.

Dave

 

Dave: thanks. i have been driving the car at +24 for a few months with the following effects:

- the cold start is generally good meaning the engine cranks and starts with one or two turns of the key
- the engine idles around 1100 rpm in park, at temperature
- in drive, at a stand still, the rpms drops to 8-900
- there is a noticeable, consistent miss in park or in drive at a stand still (i already installed new plugs/wires/dist cap/rotor/pick up coil/ignition coil & amplifier)
- i did lower the idle to 750ish several weeks ago but it's back to 1100ish. i did not check the timing back then
- once the car is at temperature, i have to make 3 or 4 engine start attempts before it starts but it has a weak idle and will stall if i don't rev the engine between 1000-1500 for 20-30 seconds then it will settle in at the 1100ish rpm mark. i thought maybe my fuel pressure regulator is going? where does one measure the fuel pressure? i could not find a schrader valve on the fuel rail like i had with my '90 & '91 xj40s.

tomorrow, i will get the car to normal temperature, adjust the timing closer to +17, re-set the in park idle and drive it for a few days.

 

although i have a 6, do i follow the same procedures as shown in the video to check and adjust the fuel pressure?

 

Ren, I'm afraid we are above my pay grade already for the Jaguar engine, I don't have one. My comments were based on common conditions that would be seen on a Chevy V8, for example. But let me think out loud on the symptoms you've mentioned.

- A clean cold start would tell me that the mixture is slightly richer than normal (as it should be), the timing is not a problem, and you have sufficient spark. What is the cold idle rpm?
- 1100rpm idle at normal temp seems high to me. My shop manual says 800rpm is the target, but it doesn't say whether that's in park or in gear.
- 200-300rpm drop between park and drive (in vs out of gear) again seems on the outer edge of normal, but I can't find a spec for the drop.
- Is the miss in park/gear a consistent complete miss, like you pulled the wire off the spark plug, or a sputtering, erratic, weak miss, (maybe, too much advance or too lean mixture). What happens when you start off slowly from a stop and accelerate to highway speed? When does the miss go away?
- I'm not sure how the idle speed is set/controlled on this engine. I believe the ECM only controls the the fuel system and the injectors, but there must be some sensor input to the ECM. The fact that the idle speed returned to 1100rpm after awhile seems to support this. But I don't know why it would return to 1100rpm, which is excessive.
- Hard starting when hot could be from leaky injectors or cold start injector (I don't think that is the name for it) or something allowing excess fuel into the engine. And on the other side, it could be from a very lean mixture which could be caused by a weak fuel pressure regulator. The fact that you have to rev the engine can support both conditions also. If there is an overly rich mixture at hot start, increasing rpm will "clean out" the extra fuel and return the engine to a normal idle. On the other hand, a fuel regulator with a return line (yours) is typically managed by vacuum. At idle the vacuum is high which make the regulator reduce the fuel pressure, engine doesn't need much fuel. As vacuum decreases, the regulator increases the fuel pressure because the engine is being loaded, foot on the gas pedal. At WOT (wide open throttle) you have maximum fuel pressure and near 0 vacuum. So when you rev it for a bit, the vacuum will go lower and increase fuel pressure slightly giving the engine a little more fuel, but still causing a crummy idle. Testing the fuel pressure would be a must-do in my opinion, but I didn't fully understand what happened on the YouTube. It looked like he disconnected the pressure line to attach the gauge, but then he started the engine and it seemed to run smoothly on all 12. I think the better approach would be to cut the flex hose between hard line and regulator and install a simple "T" and then attach the short adapter hose he built permanently to that. If I remember right, he had about 28-29psi at idle and the shop manual says 36-39psi max. The fittings he used for attaching the gauge to the adapter hose look like ordinary shop air hose quick connects, should work.
- My personal opinion is that the additional 7* of timing is not your biggest problem, I think there is an issue with your fuel system and maybe the added advance isn't helping.

Dave

 

Too much advance at idle can cause a misfire....although I'm not sure if 7º is enough to do it.



You made this adjustment at the Air Distribution Block?


Disconnection the hose to the cold start injector and use the now-vacant nipple on the fuel rail for your pressure gauge. Also, remove the vac hose from the fuel pressure regulator and check for any raw gasoline dripping....which would mean a leaking diaphragm in the regulator

Cheers
DD

 

Doug: adjusted the idle downward here with my nifty, custom fabricated allen wrench. ren

 

I would be checking the TDC mark on the harmonic balancer is correct before doing any ignition "tuning"

 

OK, good, that's the correct method.

You might consider removing the Air Distribution Block and cleaning the passageways. They can gunk-up...which might be causing your varying idle speed. Order a new gasket before taking on the task.

While you're at it, clean the throttle body bore and make sure the throttle blade gap is set to .002"

Cheers
DD