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90 XJS V-12 won't start

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Michael J.

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I did a complete rebuild on a 90 Xjs V-12 with Marelli Ignition. When installing the timing chain, I positioned the crank so that timing mark was cylinder 1-A TDC. Used a Cam Guage. Engine turns over freely, but won't start. Ignition fires correctly with inductive timing light, but the engine seems to fire during exhaust stroke. I used new Bosch Platinum plugs with the called for .025 gap.

If valve timing was off, would engine have bound up when turning over with a wrench during the build?

I have looked for air leaks, found none.

I am fresh out of ideas. Any thoughts anyone?
 
Check compression to verify valve timing is close, Check TDC for the A1 piston, make sure that the dist. rotor points at the A1 when it's at the TDc mark. You can use a balloon on the compression guage hose to find the A1 firing position, as the ballon fills, the timing mark should come around, and the rotor should point to the plug lead for A1. Dont crank this engine backwards more than an in., preferably not at all, just take your time.MM
 
What do you mean by cam gague? The factory locking tool, or something else? If you put the cams in on overlap instead of TDC, you won't get any interference with the valves, but cylinders aren't in right order either. Air cleaners must be on or the bolts back in the throttle bodies, major air leak without them. What about injector pulse?
 
The Cam Guage was obtained from XK's Unlimited and is like the factory tool in that it fits in the notch for each cam.

Everything was buttoned up and ready to go, but the engine would not stop.


What I found tonight was that with the fuel pump relay and the main relay removed to depressurize the fuel system to remove the injectors and rail, the pump still runs if you hook up the battery. So, I'm looking at the possibility of a possible fuel pressure problem, but now that I have the r/h intake off and the valve cover, I'm going to verify the valve timing.

More to come.
 
"Curiouser and Curiouser"...Well the timing is correct. But it looks like the fuel boost pump runs continously. How could that be? The wiring diagram shows that a power wire goes from the fuel pump relay contact to the two O2 Lamda sensors. Disconnect both sensors and the power goes away and the boost pump stops. I changed the sensors and the problem returned as soon as the battery was connected, this is still with the relay removed. The power flow traces back through the shielded wire for the O2 sensors and back to pin 24 and pin 6 of the fuel injection ECU.

The ignition is off at this point.

Two questions:

1. Anyone know where I can go for a wiring diagram for the internals for the ECU?

2. Is there something else that can cause this?

I am still tracing wires in the engine bay looking for a short that could be the source of power to the sensor wires. I am really baffled. I don't know the next step. Any Ideas?
 
check your ground wires. Just one ground missing, and the power will backfeed through where it can. Same reason a bad ground in a taillamp will make a turn signal, or some other light come on dimly. Isn't there a knot of grounds to the passenger side intake? I can't remember offhand. If you forgot one, that could be it.
 
Following Clint's advise, I looked for grounds. What I found was the O2 sensors sooted up, heavy soot. I replaced with a pair of old sensors and the boost pump problem stopped. Car will still not start. Still wants to fire in exhaust, TOO Rich?

I have no clue what else to try. I'm going to look for a used Fuel Injection ECU to see if that will solve it.

Any other Ideas?
 
Here's the latest.

A local Jaguar guru suggested that the catalytic converters might be plugged. So I pulled the o2 sensors and attempted to start. That would allow pressure to escape through the 3/4 " hole. Still the same. The after fire was a little more thrilling this way, but it still would not start.

The other suggestion was that the Harmonic balancer consists of two steel parts with a rubber insert bonded between them. The theory is that the rubber dampens the vibrations and absorbs torque from rpm changes. The rubber can deteriorate with age and allow the outer part to slip part of a revolution. Then the timing mark for the balancer would not be aligned correctly giving a false indication of the timing.

I was told that this was semi-common on six cylander XJ engines. Has anyone heard of this before?

I'm re-reading the factory manual on the timing adjustment again to see if this might be a factor. I'm looking for someone to check the Fuel Injection ECU for electrical problems.

It doesn't look like my jag will see the light of day anytime soon.

I also went back through some of the past forums. I found one on a similar problem, but the member (Kindofblue) finished his shop class before he found the cause.

More to come. This is a tough one. Any thoughts?
 
I haven't seen the damper rot on one before, but I have seen a couple of xj6's where the crank bolt comes loose, and the damper beats the keyway out of the crank, cuts into the groove on the pulley, and causes a misfire/hesitation/intermittant no start. I have replaced 2 12cyl. ecu's.
 
The factory manual is not clear on the crank position when setting the valve timing. When the guage fits in the notch on the cam shaft, What position is the number 1 piston?

The Marelli ignition cars do not state the ignition timing as 8Deg BTDC, etc. What is the ignition timing with the LUCAS ignition?

If I set the crank for the ignition mark on the harmonic balancer to line up with the stationary mark, would the crank have been out of place when the valve timing was set?
 
I checked the bolt for the harmonic balancer. It is tight. Thanks Clint for the tip. I wish it had been simple like that. It will take an evening to get back down to thew cam cover removed to check cam lobe position.

More to come.
 
In reply to Larry;

Exhaust Cam Lobes face out to fenders.

Pulled spark plug for 1A and verified TDC when Cam guage fit notch.

Thanks for the suggestion. Wish it was it.

Question to the group:

Is crank supposed to be at 1A TDC when guage fits notch?
 
Just looked in manual, 1A, 10 deg static Before TDC....TDC mark on crank 0 deg on cover, have you tried moving distributor, this is hard when you aren't there!!! I've got manuals but, with some motors after rebuild it takes a high boost jump machine to break in rings to get things jumping.
I know you are at wits end
, but sometimes walk away take your breath do later!
 
PUZZLE SOLVED!!!

There are 720 degrees of crankshaft rotation in one complete engine cycle of intake-compression-power-exhaust.

I had presumed that cam guage set cam at top dead center compression. WRONG, WRONG, WRONG.
Cam guage sets cam at botop of exhaust stroke.

I repositioned distributor 180 degrees and the engine started right up.

The timing light showed perfect timing with marks lined up, but the timing was 360 degrees out of phase.

Thanks to Larry Kronmeyer, Clint and Mogren for their suggestions.
 
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