X300 xjr no start driving me bonkers

I’ve posted this on another jag forum to no avail. Forgot about this site and have been coming here for close to a decade.

Hope I can get the help I need here.

It’s 1995 XJR6

Ran fine. Ran like a top. Took it for a lively spin as it’s a donor vehicle for my 78 (it’s getting the engine and I have a 5spd for it, anyway) it ran just fine, as I parked it up it died or I turned it off it was a little hot, not overheated just warmer than usual. It’s been a year, I forget. I do know that it wouldn’t start again, hasn’t since. I’ve tried everything you can imagine and only got it sputtering and smoking to life only to have it die. It’s baffling. Please keep reading:

Problem seems to be no power signal to the fuel pump relay(s) and I suspect no ground trigger to the injectors as I seem to have spark. Key on fuel pump does nothing, pumps hotwired work just fine (two in tanks in the XJR) When hotwired the fuel pump still won’t get it running. If I pinch off the return line a few cilinders catch but mostly things just sputter and grumble and nothing is as it should be.

So, here’s what I’ve done:

replaced all spark plugs
checked all fuses good a million times.
inertia switch good.
all relays swapped a billion times all working
no wiring issues. Checked all junctions and cleaned etc.
fuel pumps both work when hotwired
no in tank issues with pump hoses
coils seem good
J gate good
Turns over on the key but just WILL NOT FIRE! GRRR
Immobiliser does not seem to be the issue, check engine light stays on.

turn ignition on everything lights up. Check engine stays on. Cranks and cranks not a hint of life and fuel pump has not received any signal or done a thing. I have the back seat and parcel tray off and have tested for 12v at relay, 12v is there, switched never arrives.

Has my chip in my key bit the dust? My ecu? the BCM? I can’t figure it out. I really NEED this engine to run properly so I can pull it and transplant. I refuse to pull it b4 it runs right is troubleshooting in the new setup will be much harder.

Hope someone can think of something…

cheers

Crank position sensor would be my guess.

I think Jim has the right guess!

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Sorry somehow this portion of the post didn’t make it in:

CKPS has been tested, replaced and tested again.

250rpm while cranking.

Also tested both CKPS units in regular AJ16 powerd x300 and they work.

NOT crank position sensor. Don’t know how that didn’t get in the origional post.

But keep 'm coming! (also CKPS wouldn’t stop the fuel pump circuit from priming)

cheers

Have you carried out a compression test and if so what were the results? You say the inertia switch is ok but did you test it electrically?

If the fuel pumps are bridged across the relays will the engine run then?

I have not done a compression test. Remember it ran fine, switched off, now refuses to start since.

Tested the inertia switch by unplugging and plugging back in, things turned off and turned back on consequently. I can bridge it.

in my first post I explain that it will not run even if the fuel pump is hotwired. Only some life if I hotwire the fuel pump AND almost fully pinch off the return line. My theory being that the fuel pressure becomes high enough to ‘dribble’ through the injectors even though they aren’t being operated. Make sense?

Just a thought, heated O2 sensor? if that is bad does that inhibit FP activation?

A "Noid light"ll you for sure if the injectors are firing.
Look here:

I doubt that you are overcoming the injectors with the regulator block, but who knows? Have you looked at the pins on the ecu connector? They have caused many folks fits due to water ingress.

The lambda sensors will not stop any part of the engine firing circuit.

If your are right about the injectors, then the power input to the ecu, the CKPS wiring input, the grounds to the ecu or the ecu itself are the next suspects.

So, now my bet is the ecu connector pins…

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I agree the O2 sensor will not stop the injectors firing, what I think you will find if the O2 heater sensor relay is bad then I believe the fuel pump will not receive power.

My tach shows 250 rpm (or so) when cranking which lead me to believe the CKPS wiring is in order as assume the tach get’s it’s signal from the ecu (?). Also when I unplug the CKPS my tach doesn’t move while cranking.

ECU grounds make sense in theory but the ECU is activating other ECU drive functions like the electric waterpump for the water to air intercooler (or is that ignition triggered and not ECU, it switches on and off when I pull the ECU relay)

As for the ECU connector pins, well, I’ve checked them and checked them again. Cleaned them for the sake of it. They are clean and in good shape. Can’t hurt to look again. But I’m just chasing my tail.

Robin_O_Connor: is that a sure thing ont he lambda circuit? If so any idea where that relay for the heated O2 is located?

I believe it is on the right hand side of the engine compartment, looking from the drivers seat. Its the first large relay, there are two small relays closest to the side of th car.

  1. You have me on the CKPS wiring- I agree that the tach indication pretty much proves it is OK

  2. Yeah, BUT there are several grounds. Also several sources. It should be easy enough to figure out for sure if the injectors are firing… check the group supply lead to ground and then look for pulses from high to ground on the separate returns to the ECU. If not a Noid light, you could parallel a 12 volt led lamp across an injector. It sure would be nice to know FOR sure if the injectors are firing.

  3. In your PM to me, you said that you looked at the pins and they looked OK. In the two cases of bad ecu pins I have seen, it was very obvious the pins were corroded- to the point of being non existent in one case. So, I guess that is not it!

As a reminder… Fuel, air, ignition spark, compression, all timed right makes the engine fire.
I do not see that you tested compression or are sure the cam is turning.
You can use a propane bottle to introduce vapor into the intake whilst cranking and it will run, albeit rough, to tell if you have no fuel. You have hotwired the pumps, but you are not sure that you have pressure. Maybe the regulator? That would be consistent with clamping the return making it fire (a little).

Back to the injectors. Testing that circuit is simpler than most of what you have endured so far!

Good luck.

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The power supply to the injectors in the black with green stripe wire. It should read 12 volts to ground when the “ECU Controlled Relay” is supplying power to the injectors.
Another thought… the ECU shuts off the injector firing when it senses a WOT. It would be good to check the throttle position sensor feedback with OBD II to see what position is read for the TPS.

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Made a little progress today. Had a helper today, extra pair of hands works wonders.

Here’s what I learned today:

  • Injector pulse is present. Not the problem.

  • TPS is fine (someone suggested ECU reading WOT disabling fueling). Hooked OBD reader and TPS voltage is in line with the pedal action.

  • It can run smoothly on brake cleaner. (which would rule out compression/timing/ECU and all other issues besides fuel delivery)

So it has to be FPR, bad fuel or bad fuel pump. I haven’t tested fuel pressure yet…

Here’s how I reached the above:

So, got my helper to crank the engine over, I had removed the air cleaner and had gotten a bit of life in the past with brake cleaner as fuel but not much. that was on my own at an awkward angle. Now able to look right at the MAF screen I was able to liberally and carefully dose the brake clean while my helper cranked the engine.

Presto. It came to life and I could keep a buttery smooth steady idle by pulsing my brake clean input. It was great to hear it run again! We tried to match extra throttle and extra “fuel” and it picked up pretty smoothly.

So that’s a relief on some fronts, creates more questions on others. I guess most important is, what’s next:

Replace FPR. Drain fuel, refil with good fuel. Check fuel pressure. Once that is all done and I have good fuel and good fuel pressure I can’t see any reason why a hotwired fuel pump shouldn’t run the engine. Then the next step will be figuring out why the pump isn’t kicking on.

Something else I noticed again today that I’d forgotten is that the fuel rail and/or FPR make a REALLY loud hissing sound when the fuel pump is running, an abnormal sound if you ask me. It goes away when I pinch off the return line… My x300 4.0 sport doesn’t make that noise.

Seems like I have multiple issues on my hands that just happen to coincide and be fuel delivery related. Thoughts?

cheers.

Fuel does sound as if it is the culprit, on two fronts and the first to mind is ethanol and it drawing in water causing bad fuel. I think that in the US you can get an additive that can help cure that, thankfully we don’t have much if any ethanol in fuel here in the UK.
Second is the noise being caused by a blocked breather in the fuel tank causing a vacuum and interupting the flow? Another thought is the drain under the filler cap blocked causing water to collect there and then contaminate the fuel especially it has been outside while it was laid up.
Sounds as if you are slowly getting there, so good luck today.

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While I don’t subscribe to the “ethanol- root of all evil” dogma of my friend Neil, he might be right that you have some water in the gas tank. That is easy enough to check, just capture some fuel from the rail into a glass jar and look at it. I worked on an XJR for a while before I figured out that it had gallons of water in the tank (from the drain problem Neil described).

I sure wish the Jag engineers had made it easier to check fuel pressure on an X-300. At least a port with a pipe thread or something!

It sounds like you are close. You have proved you have tenacity. I would have probably quit a long time ago on a donor engine! Of course, with enough time, tenacity overcomes good judgment.

Keep us posted. It is a good tutorial of “no start” on an X-300.

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Ross, with due defference ethanal like alcohol is “hygroscopic” and draws water from the atmosphere when humid. But yes the drain issue exacerbates that too.

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Before you say it I also do typo’s! Ethanol.

I didn’t have time today. But I will drain the fuel and replace the FPR. The 4.0 and the XJR FPR look different, both Lucas units though. I have to take a good look.

Tenacity/I refuse to be beaten by a car/moronic willpower :wink: who knows what to call it. And just imagine the end result, a gorgeous silver on black, 1978 European XJ6 (with old style mirrors) lwb former 4.2/auto car with a supposed 170-ish hp and that horrible th400 based box draining at least 30 of those to a 5 speed-minimal emissions required to keep it running right-firebreathing 320hp/511nm refined monster. Rear diff replaced with a 3.31 or 3.54 Posi. Frankenstein in a tuxedo. A 1978 xj-R-. I’ll have to find someone who can copy the XJ6 badge and make an XJR badge… anyway, those thoughts keep me going once I come back inside and have a cup of tea. lol

I’m in Europe btw so fuel is not horrible. But either water in fuel or bad FPR is what it has to be…

Before you say it I also do typo’s! Ethanol.