Hello all.

If you have seen my other posts you know that I have fixed my transmission problem and am on my way to fixing my smog issue. Now I'm having another problem.

When at wide open throttle (WOT from now on) it hesitates and won't go over roughly 3k rpm but when I'm about 3/4 throttle it accelerates smoothly which I didn't notice before because I was driving on flat roads. During a test tribe yesterday I drove through some hills and the kickdown was on point but when it shifted in to second @40mph it acted as if 3k rpm was its redline if you will. So my first though was fuel delivery. I've replaced the fuel filter and the fuel was a tad bit nasty but nothing too ridiculous but I'm getting terrible fuel mileage which leads me to believe that it's not that I'm not getting fuel but maybe I'm not burning it properly. It has an exhaust leak right before the mufflers and I can smell unhurt fuel but not to the extent that I thought I would be.

Any clues as to where to start.

Ps spark plugs are new, distributer cap&wires look relatively new and I haven't had the cap off to inspect the rotor just yet.

If it would help I can have a buddy film from inside the car to giver everyone a better picture.

Thanks in advance. Kyle

 

My first thought is under-fueling. Lack of delivery (weak pump, clogged filter type of thing) or metering (injectors not staying open long enough). The former is easier to chack for, especially if you have a pressure gauge.

You might pull the new filter and empty the contents into a clean jar. What you see might dictate your next steps.

Also check that you distributor vacuum advance and mechanical advance is working. Lack of advance would give low power and poor fuel economy....although I'm not so sure it was cause the 3000 rpm limit symptom. Worth checking anyway.

Overfueling is a possibility....but it would have to be gross overfueling as engines at WOT *like* plenty of fuel. It would take quite an excess to choke the engine down to 3000 rpm and you'd certainly see lots of smoke in your rearview mirror.

Others will chime in

Cheers
DD

 

I'll pull my fuel filter off and check that out today as well as making sure the vacuum advance is working properly. Aside from making sure the vacuum hose itself isn't leaking is there another way to check that? I don't have a pressure gauge but I can grab one from the parts store today as well.

Thanks Doug!

 

Get it pressure checked and read about the "hammer test" and heat test...my truck acted the same way when its cat died....

 

Hello Kyle, my series III xj6 used to do the same thing! Frustrating I know =/ Anyways, the solution I found that worked for me, with the help from the experts on this forum, was as simple as replacing the ignition coil. I don't know for sure that the coil is the culprit in your case, but a shiny new one certainly wont hurt your jags performance
also, just recently I replaced the distributor with an aftermarket pertronix flame thrower, and wow what a kick! the throttle response is better than ever and my jag loves WOT! The diaphragm in the vacuum advance on the stock Lucas distributors wont last for ever, and when they wear out (like any diaphragm will) its goanna be felt, in fuel mileage, and performance.

 

This might be the best answer, I just pulled the plug off of my ignition coil and there's oil inside the rubber boot and around the connecting points...Never seen that before and I don't believe it could be a good thing. I am going to price out coils today and see if that works! Thanks

 

Remove the distributor cap. Now apply vacuum to the vacuum advance hose (use a hand pump ....or even lung power). You can actually see the advance mechanism move in the distibutor. If it does, you know it is at least fundamentally operational.

Also check the the vacuum hose in in good shape and correctly attached to the vacuum regulator under the manifold. We can dig up a diagram on that if your underhood label is missing.

For the mechanical advance twist the distributor rotor and release. It should snap back against the mechanical advance springs.

The best way to check either, though, is with a timing light.




Attach it to the nipple on the fuel rail that feeds the cold start injector. You'll have to remove the cold start injector hose first, of course.

You should have 36 psi while cranking

Next, attach a long hose and tape the pressure gauge to the windshield so you can see it while you drive.

If the pressure suddenly drops wayyyy down when you hit 3000 rpm, you're on your way to diagnosing the problem

Good suggestions from others on a clogged cat converter and weak coil.

Cheers
DD

 

So I called a few auto parts stores and priced out the coil. They told me that the coil for the XJ6 is 60$ if I order it (5 day waiting period) the Jaguar specialty shop has one in stock for 75$. But here's the weird part, pep boys has one for the Vanden Plas for $11.99. Is there a difference between the regular XJ6 coil and the VP? thanks

 

well I would think that any coil that works on an xj6 or vanden plas would be interchangeable they have the same engine. I know the Lucas and bosch ignition coils for the 84 xj6 and vanden plas are the very same coils with the same part numbers. I found a Lucas for about $28 and a bosch for $38. However, I did find a standard motor products coil for $12, but it was only listed for the vanden plas not the xj6. I don't see why the $12 coil wouldn't work, and I do appreciate a good bargain, but that just almost seems too cheap for me. I know I wouldn't pay $60 for a coil and have to wait around for it, and I wouldn't want to pay $75 either. In my opinion you'd be best off going online at parts geek and paying $28 for the original Lucas coil. its still a good price and you know its going to be the right coil.

 

I went ahead and ordered the 12$ one because they told me they could get it by tomorrow. Worst case scenerio it's a piece of junk and I can report to those of us that didn't know. Thanks for the advice though I will let you know if it cures my sickness.

 

No difference.

Some the catalog listings from various suppliers get corruspt over the years....if they were ever accurate to begin with. Even among Jag guys there is sometimes confusion on the subject. Jaguar itself changed part numbers and suppliers a few times over the course of Ser III production

On Ser III 4.2s I've had best luck with the Lucas DLB170 coil...which is actually intended for V12s.

More commonly it's pretty been well accepted over the years that any 12v coil with about 1.0 ohm primary resistance will work.

Cheers
DD

 

It is also possible for the in-tank gauze filters to clog up especially when fuel demand is highest. Try swapping tanks on the move when you hit the problem and see if it temporarily disappears, (until the filter in that tank clogs up too !).

These petrol tanks can accumulate an awful lot of crud over the years

 

So today I replaced the plug wires and the ignition coil, still nothing. It runs a lot smoother when revving slowly still at WOT it is stumbling. I took a video to give everyone a better idea of what's going on. Thanks!

(I've spent the last 15 minutes trying to get this video to show up and for someee reason I cannot figure it out.) So for now here is that link.

IMG_6663.mp4 Video by veedubb6677 | Photobucket

 

I will do some research on that for sure. That sounds like a headache of a job. Is it one of those intimidating jobs that aren't too bad or will it suck?

 

Sure seems like a fuel delivery problem to me....as though fuel can't be delivered fast enough under a sudden demand.

However....

It also seems like a clogged exhaust.

Have someone rev the end hard while you use your hand to feel output from the tailpipes. I think you'd be able to tell if it seems restricted.

Or disconnect the pipe from the exhaust manifold.

Or remove the oxygen sensor and give it a try. The oxy sensor hole isn't very big but it should allow more exhaust out and, if the exhaust IS clogged, you should feel some amount of improvement in how the engine responds.

Sorry I can't give a concrete answer.

Cheers
DD

 

Thanks Doug I'm gonna try and disconnect the pipe after the cat and see if I notice anything. Hopefully that will tell me what to do next!

 

I stated this in a different thread but I wanted to point it out in this one as well. It drive perfect until my water pump failed and I overheated (not enough to damage anything to my knowledge) but that's when it started hesitating at WOT.

 

Well I did the "hammer test" on the cat and all seemed to be well nothing moved around in there and there seems to be pretty good pressure coming out of the rear pipes. I did notice that the cat installed on the car does not look OEM because of the welds and the way it bolts up to the manifold. Is it possible that a "crappy" universal was installed and could be doing anything?

 

The cat on the engine below the manifold "Looks" stock to me. (NOT an expert.) Did you bang on the cat farther down the line. My series three has another converter just behind the transmission that splits off to both forward mufflers.

 

Just saw the video - and yes, my first thought would be clogged exhaust... but I know how hard that is to verify. Honestly - I would go with Doug and seperate the cat where it connects to the manifold. It is really NOT that hard. 4 bolts, (Both sides of the Cat for both sides of the manifolds - 8 total.) the inside/aft (Behind the cat, and close to the engine) are a little tricky, but as long as they are not rusted too badly, they should come free. USE WD-40 or something similar. It will be loud as hell, but you will know in an hour if you have an exhaust issue or a fuel/timing problem. If the bolts wont come, strip them and/or break them - they are easily replaced, as well as the exhaust gaskets (Donuts) between the cat and the manifold.