...well, "rebuild" might be overstating it, but I've done a lot to it...

new injection hoses and home-made injection harness
new vacuum advance unit
rebuilt distributor (centrifugal advance was frozen, but no longer)
replaced all wiring that went over the engine (all the new wire is cross linked poly).
removed cruise control (I'll never use it)
removed A/C temporarily
new spark plugs and wires

So, yesterday was the big day to fire it up after all the changes. It coughed slighty, then started, then ran straigh up to 3000 RPM in no time (and this was with no throttle input from me) and stayed there.

I very quickly shut it off, inspection connections and such, and tried it again with the same result.

Any thoughts on what might be going on here? With my having made so many changes I'm not sure where to start.

Thanks,

John
1987 XJ-S V12, 62000 miles

 

Just a few to start with, others will follow:

• remove air filters and check throttle butterflies are closing,
• in B air filter housing, cabin end, block off inlet from extra Air valve,
• when you removed the cruise control, did you block off the vac hose takeoff that comes from under the A bank throttle body?
• check all the vac takeof ports on the manifolds are closed off or attached to something, and that the other end of the something is attached to something else
• brake servo vac takeoff attached to manifold and servo
• CC throttle cable holding capstan open?

Got to be air getting in where it should not, just have to hunt it down, once found can be repaired/fixed..


Greg

 

It is getting too much air from somewhere, also check for leaking PCV hoses.

 

Well...my problem has half gone away...it's now idling at about 1600 RPM.

All the takeoffs I've been able to find are now blocked. I did try adjusting the idle screw, it's now all the way in. After that I blocked the inlet for the extra air valve. I also double checked the capstan, it's sitting against the stop, fully closed.

One thing I immediately noticed was a mechanical clanking sound, which I now think is the centrifugal advance weights (the advance now being "unstuck") banging. After I got use to that sound I could hear what sounds like an air leak towards the back of the engine, and I think on the A bank side. The problem is going to be finding it. The thing is noisy at 1600 RPM, and I'm not sure how to narrow it down. I did make sure all the intake manifold bolts on the A side are tight (I'll do the B side tomorrow).

Are they any clever ways of narrowing down an air leak?

Thanks,

John
1987 XJ-S V12, 62,000 miles

 

yes ,take can of spray starting fluid, with the engine running, spray slowly around any manifold joints where they join the head,etc. if is air leak engine will rev up some.

remember fluid is flammable. a spark can light it off also.

 

I finally got the idle down to 1,000 RPM. There were a few cut vacuum lines that I missed before. Intrestingly, it still sounds like it's sucking in air up top somewhere. I tried the starting fluid trick, and just got a nearly indetectable increase when spraying into the openings for the shaft that holds the A bank butterfly.

If, with the engine shut off and the butterfly throats capped, I were to feed compressed air into the inlet system, would that cause any harm? I can't really pin down the source of the sucking noise with the racket of the engine running.

Thanks,

John
1987 XJ-S V12, 62,000 miles

 

Well...what a dumbass! After enough searching with my can of ether I (for some reason) just stuck my hand under the right intake manifold and realized there are two ports, not just one on it. Blocking it solved my problem. Thanks for the advice!

John

 

you said it, not me!! hehe