Hi all,

A pleasure to finally join a community of Jag lovers. I've been battling this issue with my 83 Vanden Plas. The vehicle would start up no problem and drive decently for a bit and then out of the blue, start to misfire, the idle would drop very low, and I would have to keep my foot on the gas pedal in neural to keep it from dying at a light. In the past, it also sort of had these hick ups driving under load while the engine was under 3k rpms (highway driving). That has largely gone away. My thought thus far is perhaps injectors?? Today I pulled out injectors 5 and 6 (first two from the front of car ) and tested them. They seem to be clicking alright...

I've replaced/verified a few things thus far:

1. Verified fuel pressure and replaced fuel pump

2. Replaced ignition coil

3. Rebuilt ignition pulse module

4. Replaced spark plugs cables, cap and rotor


Anything else I am overlooking?

 

Welcome to the forum 4JJag21, unfortunately I have not a lot of advice to offer you. Your experience mirrors mine, I assume you have the 4.2 litre motor. I have been chasing this problem now for over a year with little advancement. I also drained both my tanks and flushed them out which was useful as there was water in both of them. I have finally given up and taken the car to a mechanic to try and fix when he has a spare moment or two. He did say that there was water in the tanks again and that both filler drain holes were blocked letting water back into the tanks as the filler lid seals were not real good. So maybe thats a something to check? Also you may need to check that the injectors don't just click but allow a good spray of fuel into the manifold. I know mine were clicking but not spraying properly. If you have a problem with dirty fuel it may be a good idea to fit some pre fuel fiters between the tank outlets and before the changeover valve in the boot. That'll save your change over valve and fuel pump from premature wear.
I'll let you know what my mechanic comes uo with but may be some time. Meanwhile if yiu turn anything up please post it so we can all know,
Con

 

I'll check compression shortly to make sure that I'm at least maintaining cylinder pressure.

I did have an issue before with water in the fuel tank previously so I'll check that again.

There are 4 new injectors coming. I'll pull them all out and inspect and replace the worst ones.

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I'm just two sips into my first cuppa coffee so what follows is a bit random. Intelligent conversation later, perhaps

Check/clean/tighten the bundle of ground wires at the rear of the water rail.

Inspect/clean/repair wires at coil, coolant temp sensor, and firewall mounted relays. Give 'em a little jiggle test with the engine running.

With the engine warmed up, unplug the coolant temp sensor and use a paper clip to bridge the contacts in the connector. Any change in running?

With the engine running jiggle test the wires at the back of the ignition switch

Use a jumper wire to connect the coil "+" post to the battery "+" post. This bypasses the ignition switch. Any change in running?

Unplug the fuel pump relay. Look at the connector plug and determine which terminals are associated with the white wire and the white/green wires. Jumper together the white and the white/green. This bypasses the fuel pump control circuit. Any change in running?

Inspect/tighten the ducting between the throttle body and the air flow meter

Cheers
DD

 

Thanks for your response DD. I double-checked and re bonded the bundle of ground wires which I believe are responsible for the injectors. I also replaced the fuel pump relay, replaced a few sections of wire on the harness including wiring to the coil.

I haven't done the coolant temperature sensor bypass test yet. I'll do that once I get the injectors in!

 

I'm assuming the fuel filter has also been changed. If so- Are you building any pressure or vacuum in the tanks before ,during or after running?

 

Correct, replaced with a new oem bosch filter and fuel pump.
Thanks for the comment

 

I didnt realize you had responded before editing my post. are you building vacuumor pressure in the tanks. plugged evap will starve it for fuel. a good way to test is just leave the cap loose while running

 

An extra that just might work.

1. Down and under. Remove and clean the braided ground strap loated at the right of the engine. At the place that the transmssion meets the engine.

2. Top side. Add a ground cable. From the battery - on the right wing wall to the engine block.

A similarfix did so much fo9r my car.

Carl

 

I once developed a bad intermittent miss after a little routine maintenance. There are 2 white wires which feed the cool and the connectors were not a tight fix and i had bumped them. Fix was to remove connectors and slightly compress with pliers and refit so they were nice and tight.

when you have a miss does your tachometer needle shake much? If so it might be worth checking the white wires to the coil.

have you looked at the fuel Tank change over valves? After I had water in one tank they did not work properly and I had to replace them. In Australia new valves are no longer available and the first (used) valve was also not good. The second one I tried made a big difference. If the valves are a problem a sign might be your fuel pump becomes noisier after you have driven for a while.

good luck.