I've currently got a P0174 code (no other codes) that I can't source. I can clear it and it will be back pending in a few minutes @ idle or after a drive around the block.

A little background, I bought this car running poorly. It was a good deal and I've always loved Jags since I used to drive my roommate's XKE back in college.

When I got the car it was running lean and blowing black smoke out of the driver's side. It had a P0174, P0151, P1797 code. Fuel pressure was off the chart at 86psi, a kinked return line at the tank was replaced (previous owner said he replaced the fuel pump I don't think he disconnected the fuel lines, they appeared to have been bent after being stretched straight and then pushed back and kinked) and the pressure is now 41psi. The MAF readings were out of range very low g/s so I replaced with a used MAF that is in spec. I also replaced the front O2 sensor on the driver side, it was very fouled and had no voltage reading. The other side and 2 rear sensors were reading voltage. Tightened grounds from the battery to all fuse boxes and engine compartment. The idle was smoother after these repairs and visible smoking was gone. I hard reset the battery and cleared the codes.

P0174 returned. The hunt so far:

Because I thought I might have jumped time, I checked and had not. While I had the covers off I replaced the secondary tensioners, changed the plugs and reinstalled the valve covers with new gaskets. Cylinder compression avg 145psi per cylinder. Air cleaner looks fairly new and clean.

It seems like a vacuum leak. I have sprayed brake cleaner everywhere I can conceive of there being a possible vacuum leak and listened for an idle change and watched my meter for a trim change> nothing. Tried soapy water, also > nothing.

At 715 rpm idle:
SHTFT1 -0.8
LNGFT1 -2.3
SHTFT2 19.5
LNGFT2 14.8


Rev to 1800 rpm:
SHTFT1 0.0
LNGFT1 3.1
SHTFT2 19.5
LNGFT2 8.6

Hold at 2500 rpm
SHTFT1 0.1
LNGFT1 2.3
SHTFT2 19.5
LNGFT2 14.8

Take foot off accelerator dropping quickly back to idle:
SHTFT1 0.0
LNGFT1 3.1
SHTFT2 0.0
LNGFT2 14.8

at idle SHTFT 2 rises back to 19.5

I did a diy smoke test and did not find anything. I used compressed air and listened with a stethascope and did not hear a leak. I have reamed out the part load breather and cleaned the throttle body.

Pulling off various vacuum lines makes no change in the SHTFT2 & LNGFT2. Revving the motor can make a temporary change (see above) that will return to the lean trim codes.

I'm stumped

 

May be one of the injectors on that side is malfunctioning due to the previous high pressure. Could pull the plugs and see if one is black.

 

Do you have any misfire codes or does the car idle smoothly? If it runs rough you could have a bad coil.

Without burning the fuel to consume the oxygen the O2 sensor will read lean and adjust the fuel trims UP.

 

No misfire codes or any others, runs smooth at any speed.

 

Sure sounds like a vacuum leak. Common places are the part load breather hose - the one that goes under the intake manifold - and it's connections. The trunking that goes from the air filter to the throttle body, in the folds particularly. Or the evap purge valve on the firewall that one of the ends of the part breather hose connects to, if it sticks open.

 

I've had most of the tubes off when I did the secondary's. I did an inspection of most of them. I tried the cigar method of smoke test with a rubber glove on the end of the air filter tubing and blowing smoke into the part load tube on that side. The glove would expand under the pressure and s l o w l y leak down. No smoke visible in engine bay, I assume it wandered out the exhaust. Pulled the vacuum line off near the master cylinder and smoke came out, likewise when I pulled the line by the fuel regulator to test the "reach" of the smoke.

I will check the purge valve. Looking for testing procedure.

Maybe someone can explain this phenomenon; when I pull the vacuum line off the left side part load breather hose at the valve cover I have a tremendous vacuum and the car stumbles, almost stalls. SHTFT1 & LNGFT1 jump around to compensate SHTFT2 & LNGFT2 do not waver from the 19.5 and 14.8 respectively. Then if I plug the vacuum line but do not reconnect it to the valve cover the trims SHTFT1 & LNGFT1 balance back out but the SHTFT2 & LNGFT2 never change. I had noticed that removing the oil filler cap and/or pulling the dipstick made no variation on the SHTFT2 & LNGFT2. Also when I reattach that breather line (which has alot of vacuum) back to the valve cover there is no vacuum when I take off the oil cap, I placed a piece of a rubber glove over the opening and saw no sign of it being sucked inward.

So I got my trusty allstate vacuum gauge and T'd into the line by the regulator and I have a constant 18psi of vacuum between idle and 3000 rpm's.

Is there a method for plugging the vac lines and adding them in one by one to find a leaker?

_________
98 VDP

 

I think you have a dirty injector (or two): clean the MAF sensor, run an bottle of GUMOUT's Best through. This used to work (and hold for 3 months) on my RRS/SC when I got that code.

 

Check out this thread -

https://www.jaguarforums.com/forum/x...01-xj8-103225/

This sounds similar to your issue. He did the smoke test and no smoke was coming out anywhere. If I understand it correctly, the problem was with an orifice in the PCV hose/system that is supposed to restrict air flow.
About the evap purge valve, I think you could remove it and plug it (the hose) to see if things get better. Theory being, the purge valve only opens on overrun, and would produce a vacuum leak effect if stuck open. I may be way off base here, but in this thread there is some good info and stuff about the purge valve at the bottom.

https://www.jaguarforums.com/forum/x...2-p0175-99872/

 

I've been running on a tank of Chevron 93 with a bottle of Techron Concentrate. The MAF is new/used and I cleaned it before installation. I don't have any codes that I would normally associate with injectors and it runs and idles smooth.

I pulled the vacuum line of the Evaporator Purge Valve and it did make the car run rough and the bank 1 numbers fluctuate. This happened to a lesser degree when I unhooked the wires to it. When I hooked them back up it went back to the prior state.

JimmyL, I had previously reamed the orifice with a 3/32 drill bit and so I know its clear and it it definitely in place. I was able to get the motor to run worse but not better by plugging the hose and orifice.

I checked the ECT and IAT with a cold engine and they appear to be fine.

I swapped the upper o2 sensors at the plugs hooking bank 2 to 1 and visa versa. Begins to run very rough and the trim codes swap too -
before swap:
SHTFT1 -0.3
LNGFT1 -2.0
SHTFT2 19.5
LNGFT2 14.8

after:
SHTFT1 19.5
LNGFT1 14.8
SHTFT2 -19.5
LNGFT2 -15.6

Doesn't that seem to indicate the bank 2 , o2 sensor is bad or possibly the wiring? This is a new/used sensor, it may have been fouled by the rich carbon build up? My meter shows voltage and activity, the one I replaced showed no electrical activity and was almost solid caked carbon when I removed it. I have another one I can try, what do you guys think?

 

Sorry, previous post was wrong.
One or two injectors may be blocked, causing the fuel trims to send more fuel to the working injectors to compensate.
If it was a vacuum leak, both sides of the motor would be affected.

 

Hmmm, well what fredd60 says seems logical to me - that if it was a vacuum leak both sides of the motor would be affected to some extent. So, the O2 sensor for that bank might be bad, or could be an injector blocked on that bank. I'd definitely try another O2 sensor if you've got one.

 

CONCLUSION: The first thing I had done was replace the O2 sensor, the original one was terminally fouled and never showed voltage. After fixing the kinked fuel line (high pressure return) and and replacing the MAF (voltage out of spec) and being certain there were no possible vacuum leaks I probably ran less than 20 miles trying to diagnose the continuing problems and in that time I completely fouled this new O2 sensor. Replacement of the O2 sensor (3rd sensor in the toughest location to change) fixed the problem and returned trims to spec. All numbers are good and my car runs like a dream. The odd shifting pattern of lurchy, not hard, shifts are smooth now as well. Now to a tranny filter change and valve block inspection.

 

Thanks for the update and good to here you cracked it.