Ross,
I see that now you are back you are firing on all cylinders! No duff coils about you.
Well, I donāt know about my coils but plenty else is duff about me!
As to the bad coils, I think we would all agree that the OBD II implementation on the X-300 leaves a lot to be desired especially about misfires, BUT if a coil sets a misfire code, it will very likely point to the correct cylinder.
Hi Ross,
What if the code is 0300 Random misfire. (I think that is the correct code number). There is obviously no cylinder identification. I have gone through the Jag list of things to check ie Plugs, coils, cyl. compression, fuel pressure etc. Iāve had it in to a reputable local shop and they couldnāt find the cause.
The car in question is a '95 X300 with 160k miles. Symptoms are engine slows as if the fuel is restricted then it will suddenly come back on song. When it slows I give it more gas to maintain speed and get quite a shock when it comes back again and picks up speed.
Any ideaās would be welcome
Syd. Merron '91 xj40, '95 x300
syd:
I think that code without a specific cylinder code would rule out a bad coil and probably an injector. You did not mention if you had changed the Crankshaft Position Sensor, the one at the front of the engine. It would be difficult to test for intermittent pulse loss, and it is comparatively cheap. Another thing to check is the terminals on the ecu- they are known to have corrosion problems due to water ingress into the right side kick panel. Fuel pressure is a bi**ch to check on an X-300, so I donāt know what to suggest there except hope you find it before you have to check the fuel pressure!
Good luck!
Ross what is so difficult about checking the fuel pressure on a X300. I simply hooked a gauge in the fuel line in the engine compartment . as I did in the XJ40. Am I missing some thing here?
Syd:
Most modern cars have a shrader valve available on the high pressure fuel line. X-300s do not. At least here in the US, the fittings on the fuel rail are not readily available to add a T. If you have a method to do it, please post it. I am sure orthers will appreciate it. It sure woulkd have helped me several times!
Canāt you just cut the return hose and add a test tee? Some hose clamps on both ends and there ya go?
Wellā¦ I donāt think you mean the āreturn hoseā since that is the low pressure after the regulator and the pressure there is not really of interest. I suppose you could cut the high pressure hose and install a T with hose clamps, but I would be reluctant to having such a splice right there where a leak could spray the engine compartment.
I do. I see a pressure regulator, then the fuel rail then a return hose. Why would that section of return hose have significantly lower pressure than what the last Injector is getting?
Perhaps itās not gonna give you a spot on reading on the exact pressure the injectors are getting, but it should get you to the right ballpark.
The regulator is a bypass type device. In other words, it lets fuel out of the rail to maintain the rail pressure. The downstream side of the regulator is just a return to the tank, so itās pressure is only the small pressure loss of the return pipe.
In my experience, random missfire code with the surging you describe
is a vacuum leak.
-Ken
Ross,
Sorry for the late reply but Iāve been looking for a picture of my fuel
gauge mounted on the X300 and I canāt find it. The set up is as Bryan used
, see attachment, except I made the T a permanent part of the gauge. Itās
quite simple to attach and just takes a few minutes.
Sy.
Syd.
That looks like a good solution. I wish I had found that when i was still fighting with my X-300. I looked all over and could not find matching thread pipe nor hose barbs I was willing to trust.
I would also concur with Ken that vacuum leaks are a cause of misfires. Once I acquired a smoke machine, vacuum leaks have become much easier to troubleshoot. The differentiation for vacuum leak based misfires is that they should be accompanied by high LTFT and/ or varying STFT values.
I have used smoke to check for vacuum leaks and the only spot I could find was at the rear of the valve cover seal. Could this be considered a vacuum leak?
Would a smoke machine identify leaks on the emissions side? I had a leak at the EGR valve. I was not able to identify that by blowing smoke back into the intake. Iām wondering whether a smoke machine would?
You can definitely find evap system leaks, but you need to have the schematic and isolate the various circuits. I bought a ārealā smoke machine rather than cobbling up a redneck one so I felt safer blowing the smoke into the fuel tank circuits.
Syd:
Yes! The manifold is under vacuum for the emission control system and the air is metered into the crankcase and therefore the cam box. So a leak there will add to the air for combustion. Have you had a look at STFT and LTFT?