Hi All. Just had a new head put on my 1985 xj6 . It starts up fine ,idles good. It goes though the gears fine but, when I take it out on the highway and hit an upgrade it loses power like it’s starved for fuel. Any thought on the matter as to cause,or what else I should look for.thank you all in advance for any help.

 

An easy place to begin is the fuel filter. Remve it and empty the contents into a clean container. What you see, or don't see, will dictate your next steps

Cheers
DD

 

Is the return side of the fuel system cleared out?

 

Fuel filter is clean . Not sure where to begin with the return system.

 

Disconnect both ends and blow air through? If everything is in good order you should spray a little gasoline. If its not in good order you could spray crud or nothing at all if its really blocked up.

 

I hate to say this but, where are the ends located that I should blow air into? There is a line going into the junction next to
the fuel filter. I’m assuming that is the return line. I not sure where the other end is.

 

If you are running the stock fuel system you should be able to trace the return lines back to the tanks; it sounds like you have already found where the line ends under the hood? It sounds gross but start by blowing with your mouth first because compressed air can damage check valves. Can you post a picture?

 

The return line begins at the fuel pressure regulator. There's rubber connector hose to a metal pipe that is clamped to the front of the cylinder head and from there routed rearward, thru the fuel cooler, and then to the retrun valves and tanks.

On GP is good to check that the return lines are clear. If clogged, though, the result is typically excessive fuel pressure and, thus, pronounced over-fueling....with the engine chuffing and black smoke from the exhaust.

Cheers
DD

 

Well,I blew air into the return lines. No clog as I can tell. I’ll give it a drive this weekend to see if anything changed.
I think I’ll put a new fuel filter in also, just for grins . If there’s anything else you guys can think of , I’m open for any suggestions.
thanks again.

 

Good idea; it is not unusual for new filters to be faulty.

 

Clogged catalytic converter.
Ignition timing incorrect.
Vacuum and/or mechanical advance inoperative.
Camshaft timing incorrect.

BTW, to clarify, this loss of power was noticable only after the cylinder head was installed?

Is the transmission kickdown working?

As you demand more power to climb the hills does the engine remain smooth? Or does it cut-out/misfire/cough?

Cheers
DD

 

Check the torque on the head studs?

 

Yes, never had the problem before head install. They assured me that they went through the timing a couple of times.
I don’t think they drove it enough. It starts and idle better than it ever has. The cats. are clear. And it happens as soon as I
accelerate out of my driveway. A lot worse on hills. If I hold petal down it will go into,what I call the passing gear but the rev. Is
quite high.over three grand. Also is there any adjustment for the kick down gear or, a way to test it to make sure it’s working properly?

 

I have done that many times. Phew!!!

but, not recently.

i did try to get a siphon going in that manner it failed. not disapointed.

 

Put t in secod or low. drive. Can ou get five grand/

Your comment as to passing gear" and three grand is telling. passing gear merey means the transmssion dwn shifts to second gear.

on a flat road in driive. How fast can you drive. what does the tach read at a high speed.

mind you, I do not want t see you get a ticket or wrse by exceedeng the speed limit.

hence my comments as to low and second.

 

I have the same problem, I think it happened after I was playing with the throttle and kickdown cables because the accelerator pedal is so stiff [still is]. I noticed it mostly when going up a hill after slowing or stopping, but it also seems to be sluggish at highway speeds on an upgrade. Playing with the kickdown cable seems to help, but I think I'm going to have to have a shop properly adjust it using a pressure gauge on the trans.