Bought an xjs. 85 v12. It's missing pretty bad with an extrely rough idle. I've cleaned up the connections to the amp and points etc. anything else to try? Possibly an issue with the amp? I'm 100 miles from home in this thing. Cap and button have been replaced recently

 

Spark Plugs, Plug wires or Rotor are my guess. Where are you stuck right now?

 

Actually, how long was the Jag sitting? New fuel is always a good thing too.

 

it appears to be firing all 12. the spark is a bright blue/purple. i havent checked the injectors for pulse yet but i will do that as soon as a i get a minute. i made it home just barely. the car wont rev under load past 2500rpm. when you goose the throttle the engine bogs and then picks up. at highway speed it has a serious backfire issue. its almost as if some idiot put the new plug wires on in the wrong order. could also be a distributor/timing issue. im gonna do my best to diagnose the issue and report back more symptoms. also theres some sort of enrichment switch that is loose in the engine bay. when i depress the switch the idle slows and seems to settle down just a bit.

 

PICS PICS PICS!!!!!!!!!!

My guess would be to check the timing. You would not notice a missing cylinder I know I drove 1000km on 11 cylinders only noticed a slight miss when idling and only in gear.

 

Cap and button replaced recently would make me automatically think they have the wires crossed. Might be a quick/easy fix!

 

i hope. im going to go through all the wires on sunday and make sure theyre in proper firing sequence. im going to check the injectors for pulse and the harness for voltage. then im going to remove the distributor cap and make sure the timing is in the ballpark. any other suggestions? i know that one member (maybe JameyXJ6) was having some serious ignition issues a while back dealing with his amp and only running on 6 cylinders. i forget exactly.

Sorry for the dark pics. i took these as soon as i got home (after being on the road for 12 hours)

 

Mine ran on all cylinders, it just ran like crap. It was all in the harnesses.

 

mine doesnt appear to run any different if you unplug injectors or plug wires one at a time. i dont really notice a difference until i unplug 2 or more. maybe it is running on all 12, just not very well. do you know specifically what was wrong with your harness? or what the effect was?

EDIT: i suppose starter fluid would be another good thing to try. see if the idle evens out when i spray some into the throttle bodies. could be indicative of a faulty injector harness, unless it was just running way too rich, which could explain the backfires.

 

careful with starter fluid, the high compression on these can pop a head gasket!
I didn't notice much change when I disconnected one injector, I think the V12 has so many cylinders firing that one dead one doesn't change much.

My harness was (I'm guessing) causing increased impedance levels being read by the ECU, so it opened the injectors fully and caused it to run very rich and would foul out the plugs quickly.

1st things first. Spark. Firing order, then timing.

 

yes i agree. and it would make sense since i was having some serious backfiring issues that i wouldnt have experienced if i had been running lean. thanks for the input.

 

Again, I will ask. How long was the Jag sitting in a garage unattended? Unable to rev over 2500rpm is exactly what my Jag did with bad fuel. Get some good 93 octane and see what happens.

 

Car looks nice. Congratulations

 

i drove the car 180 miles home. it was nearly empty when i bought it. so 18 gallons of 93 octane later...

i went out and did a quick check. passenger side bank cylinder #2 has a dead injector. all other 11 are working fine. it starts easy, just wont idle or rev. still backfires.

 

things ive determined so far..

#1. only 11 cylinders are getting fuel
#2. theres some bad wires somewhere as ive gotten a little shock several times
#3. when i unplug the vacuum hose from the PCM, the idle evens out a bit and the power increases noticably.

 

The only wires with enough juice running through them to give you a shock would be the spark plug wires. If you are getting shocked, they're probably junk.

The rest of the wires don't run anything higher than 12V, and most of them only run 5V or less.

 

it wasnt a jolt, just a little bite. seemed like the wire was coming off the amplifier, but ill have to double check.
definitely not spark plug wires. ive checked them all and none of them bite.

 

1. Backfiring - check O2 sensors, if one bank is not giving any voltage feedback to ECU, it will backfire and motor will make all kinds of knocking here and there.
2. You have some "custom" harnesses, I see. I would check if injectors are firing in quadrants, 4x3, by pinching actual injector body with 2 fingers, you should feel the pulse.
3. You can only check if cylinder is firing, or not, by unplugging injector, when motor is hot. When cold, cylinder "borrow" enriched fuel from the neighbor and manage to fire, even if their own injector is dead.
4. I see that someone already played with your fuel lines and put those little clamps on the short tubes, that go to injectors. This is nice, but I also see that your injectors are original color, so chances are that some of them are junk.
I have 11 good, old injectors in my stash, I soaked them and ran them with choke cleaner on the open air, they fire well, if you need a few, I can hook you up.
5. Lastly, check fuel pressure and how clogged your filter is, you might have so much junk in your filter and pump might be weak too.

P.S. - car looks awesome, seems like a lot better deal than I got, 10 years ago Give us some stats (miles, prices, rust....).

 

90k miles, no rust that ive seen except for a penny sized blemish under the rear fenders. the rear glass leaks just a bit. $3,500 is what i paid for it. its got some Cobra type racing seats and a NADI TOURING stearing wheel thats brass with a wooden handle. the interior has been redyed black. the wood is pretty rough but the leather is very nice all around. original paint. turn signals dont work, rear running lights dont work, and the fuel gauge doesnt work. other than that and the engine issues, theres very little electrical issues. the kickdown needs adjusted, and the engine wont upshift unless you let off the throttle. could very well be TPS.

it has all new ball joints, rack and pinion, tie rod ends, etc. it drives extremely nice, very comfy, and suprisingly firm. i couldnt be more happy with my purchase.

i do have an OXY SENS light on, and only 11 injectors are pulsing. i havent switched the harnesses to see if the dead cylinder moves, or if the injector itself is bad. it has all new fuel lines and a new fuel pump. the swirl tank has been bypassed. the tank has been relined which is very nice. theres barely any gasoline smell in the trunk.
ive been assured that all the injectors were ultrasonically cleaned, but what good is the sellers word? some evidence that they have been cleaned is the new fuel lines.

if thats true, and given the fact that one injector isnt firing and the other 11 are of varying pulse frequencies in repect to each other, then i would say the harness is toast.
but i might vary well take you up on those injectors.

considering the fact that the performance increased slightly and the Bog went away once i disconnected the line to the ECU, then im certain its a fueling issue.

ive also been assured that the oxygen sensors are new. so if thats true then it would have to be a wiring issue to the O2 sensors, or he couldve lied.

my mod list right now consists of some restrictor plates to keep the engine cool.

 

well i deleted what was left of the EGR or air injection system. the air pump has already been removed by the previous owner.

cylinder 2A officially has a dead injector, so ill be needing one of those. theres lots of brittle and broken wires all over the engine bay.