Hi everyone, I'm new on here and have an issue with a car in my family which is located in Kent. (I'm in Oxfordshire and go down on weekends to try and help).

I've got an interesting symptom where I can only get the car running if I pull the injectors out slightly, around 5 to 10mm away from their sockets in the block whilst still connected to the fuel rail.

Once running, I can push the injectors back into the block and while the car is in high revs, it will respond very well to blips of the throttle, but then the revs drop low the engine runs very lumpy and will stall if the throttle is not held open.

With the injectors in place, the car will not start until I pull the rail and all the injectors out slightly again and direct the fuel spraying from the injectors into the their relative ports.

No fault codes present after getting the engine running then allowing it to stall. Also no fault codes after failed attempt of trying to start the car with injectors in place.

Engine turns over.
Spark is present at all plugs.
Fuel pump runs, terminals clean.
Fuel is spraying out of all injectors.
None of the injectors are stuck open or closed.

Armed only with a multimeter I've checked the below items at the ECU in the passenger foot-well and all seem ok.

Crank sensor ~ 1.4kohms with ac signal when engine turning over.
MAF sensor ~ 0.4v with no airflow to 2.5v with blast from airgun.
Throttle position sensor ~ 0.05v closed throttle to 5v full throttle.
Idle Control Valve ~ low resistance across coils pins 1+4 and 2+3.
Oxygen sensor 0.3v to 0.7v.

Does anyone have any ideas I can try? :/

Many thanks for any thoughts on this!

 

Hi romie,

You're new to this forum but you're obviously not new to diagnosing automotive malfunctions. Good work so far!

Your symptoms would seem to suggest an overfueling issue. A few things come to mind:

1. The voltage you are reading from the O2 sensor seems too low. It takes 20 seconds or so for the heater to bring the sensor to full operating temperature (and the ECM ignores the O2S prior to that). Once hot, the O2S output should swing between just above 0 volts and just below 5 volts. It's possible an out-of-range O2S is causing the ECM to over-enrich the air-fuel ratio (AFR), but off the top of my head I think that _should_ trip a fault code.

2. When the diaphragm in the fuel pressure regulator (FPR) fails, it can allow gasoline to be inhaled directly into the intake manifold via the vacuum hose connected to the FPR. You can check for this by pulling the vacuum hose off of the FPR, cranking the engine and watching for the presence of fuel at the vacuum line fitting.

3. Is it possible the air filter is clogged or the air intake plumbing is obstructed or has partially collapsed somewhere?

4. The Engine Control Module (ECM) enriches the air-fuel ratio (AFR) when first starting the car to compensate for the cold engine. If the Coolant Temperature Sensor (CTS) or its electrical harness has a fault, the ECM may think the engine is colder than it actually is and may unnecessarily increase fueling by lengthening the injector on-time pulses. Resistance measured at the CTS itself should range from just above 0 ohms when the coolant is really hot (120C) to 26 kilo-ohms when it is really cold (-30C).

5. A coolant thermostat that is stuck open can exacerbate the above problem by not allowing the engine to reach proper operating temperature and leading the ECM to maintain a rich AFR.

6. I'm not sure if this could contribute to your issues, but if your car has a port on the underside of the intake manifold where the pipe from the EGR valve connects (and possibly the rubber hose from the carbon canister purge valve, if your car is so equipped), that port is known to clog up with oily carbon-like buildup. If the ECM is signalling for extra gas flow from either of those systems but the gasses are not making their way to the intake manifold, perhaps that could contribute to an over-rich condition.

Sorry for the laundry list, but that's all I can think of off the top of my head.

Please keep us informed!

Cheers,

Don

 

Hi Don B, laundry list is great! Is what I need seeing as I'm exhausting things to test.

I'm an electronics guy by day, but bit of a petrol-head at heart, current vehicles:
1999 150k Transit Tourneo minibus
1996 265k Citroen Xantia (on veg)
1993 65k Kawasaki ZXR750
Couple of Suzuki GSF400

During testing I've removed the air filter so all air was being drawn straight into the MAF and it made no difference

I also removed the Idle Control Valve while it was running very lumpy in the low rpm to see if it was stuck and to allow more air in that way but it made no difference :/

Other than that I'm going back down this weekend to work on all these points you made.

Many thanks for giving me further direction!

 

damn. coolant temperature sensor ok.

Measured 3kohms across sensor pins.
Measured ground and 5V from wiring loom end when unplugged.
3V across sensor pins when plugged into loom.
3V at ECU.
When wiring loom two wires shorted, of course I measured 0V at ECU and no effect on non-start issue.

New info:
As suggested I put foot to floor and turned engine over.
This DID work!!
Lots of coughing and engine was extremely lumpy and bouncing around all over the place, but it did kind of hold a stumbling coughing run.

Lots of petrol smelt from exhaust.

So we're def going along the lines of over fueling

Now when I had all the injectors pulled out of the engine but still connected to the common rail, non of the injectors were stuck open.

And there are still no engine fault codes

Just going to second check that O2 sensor..

I'm in Kent with car now (Sat) and will be with it tomorrow Sunday - ho-hum...

 

With just the ignition on, the O2 sensor read 0.4V, which is within tolerance.

Suspecting a too rich mixture to start, I did two tests.
When only just started running very lumpy at low revs with throttle open full, I sprayed a flammable spray into the air intake, this caused the engine to stall, (further enriching the over rich mixture?).

Also, when running very lumpy at low revs with throttle open full, I blasted air into the air intake via an air-line.
This increased engine revs immediately, (leaning off a over rich mixture?).

Once up-to 2500rpm or above, the engine runs perfectly with rapid response to throttle 'blips'.
1800rpm or below the engine will slow down and run very lumpy, only continuing to run if throttle is open full.

No fuel present when pulling the the vacuum line off of the fuel pressure regulator.
Whilst running lumpy, pulling the vacuum line off the fuel pressure regulator made no change to the running of the engine.

I've removed the air filter so air was being drawn into the MAF directly, so the air filter is not blocked.

I disconnected the pipe from the bottom of the inlet manifold, I could such and blow air from my mouth from the manifold end, so is not blocked.
Doing the same to the other end of the pipe, I can only suck, not blow. It looks like there might be a one way valve in there.

Hmmm

 

Hi romie,

If you can keep the engine running long enough, it would be worth measuring the O2 sensor once it gets hot to ensure that it is switching high and low between just above 0V and just under 5V.

Your experiments with the flammable stuff and extra air do seem to confirm over-fueling or an over-rich AFR (possibly due to too little air).

I was really counting on fuel being drawn through the FPR diaphragm. Oh well.

That's good. Is the throttle body clean and the butterfly valve set to a clearance of 0.002 inch? Is the throttle cable adjusted with no slack? The cable tends to stretch over time which can lead to response problems, but as long as the TPS is adjusted properly, I don't think it would lead to a rich AFR, but an obstructed throttle body might, because the MAFS would be telling the ECM that more air was being inhaled than could make it past the butterfly valve, leading the ECM to inject more fuel than necessary and a rich AFR.

I never performed that test so I don't know if our car has a one-way valve there, but if that is a valve for a carbon canister, it may be to prevent flames from an engine backfire from igniting the fuel vapors stored in the carbon canister. Which leads me to ask:

Is your car equipped with any of the following:

EGR valve above exhaust manifold and pipe that connects to underside of intake manifold?

Carbon / charcoal canister in the front left inner wheel well liner, with purge valve and small rubber hose that connects to the port on the underside of the intake manifold (same port the EGR pipe would connect to)?

Secondary air injection with an air pump mounted above the alternator?


These readings would indicate a coolant temperature of about 16C / 60 F. Would that reflect the conditions under which you made these measurements? If you can keep the engine running long enough to get the coolant significantly warmer, it would be worth measuring again to ensure the CTS is responding appropriately. You can remove the CTS and dip the tip into boiling water to get a hot measurement, then room temperature water and ice water to completely rule it out.

I still think you need to know how the O2 sensor is behaving once it reaches operating temperature (500C or something like that).

You're doing all the right things, romie, and you obviously have the right kind of knowledge to solve this problem.

Please keep us informed.

Cheers,

Don

 

Many thanks for that, just about to crack-on again..

Out of interest, the second potentiometer in the Throttle Position Switch doesn't seem to be working.
The potentiometer that goes to the engine management ECU is functioning correctly and I get a good voltage swing at the ECU when moving the throttle, but I see there is another one that goes to the transmission? And that does not give any change in readings. I don't know if this could cause these issues?

Also:
I've not got tools yet to check below items:
Fuel pressure
Compression

I searched for the supplementary air valve, but I don't think it's got one as I can't find it and the wire in the ECU is not present, (Blue Pin20).

I started to suspect a dry joint on the ECU for one of these sensors, but on inspection the ECU looks very good.
Bit difficult to probe as it's covered in conformal coating :/

I'll get back and check the rest of these items

 

Does anyone know if I can try another Engine Management ECU, (yellow and blue sockets), with one from another XJ40?
Or does it need 'coding' or 'programming' to the vehicle like with more modern ECU's?

Many thanks

 

ok, so after a bit of a break. It seems the issue has been found!

After hearing a single 'tink' from the engine when turning over, rocker cover was removed.. and there you go. The timing had slipped out of alignment!

Below is image of cam shafts with engine lined up for TDC on #1 cylinder!



oops.

The exhaust valves were 45degrees out and had knocked dents in the tops of the pistons.

The two large cir-clips that hold in the camshaft cogs were missing! :/

At least the issue is known now.

Thanks for all the help guys, this had very strange symptoms which led me in entirely the wrong direction.. never mind, live and learn eh.