I'm struggling again in cold weather with my 2004 XJ8 at 165k miles. When the temperature drops below ~25F it cranks but won't start. After multiple attempts pumping the gas pedal with jumper cables hooked up it will eventually sputter to life but it immediately sets bank 1 / bank 2 lean codes and idles rough in restricted performance mode. Scanning the computer I'm getting the following codes:

P0171 - Right-hand cylinders combustion too lean
P0174 - Left-hand cylinders combustion too lean
P1338 - Fuel pump drive circuit low/high voltage

Long Term and Short Term Fuel trims are maxed out positive ~25% each!

Removing the vacuum hose to the fuel rail pressure sensor and plugging the vacuum port actually helps it run much better but I noticed that is just forcing the computer to increase the fuel pump duty cycle because it thinks the fuel rail pressure has dropped.

This isn't my first battle with the dreaded lean codes and I've been struggling with this problem on and off for about a year but now it is so bad that the car just refuses to start and run on cold mornings.

When I tested the battery during cranking it was dropping to ~9V so I replaced the battery but no change. Cranks enthusiastically with the new battery but still won't start reliably.

Intake smoke test doesn't show any vacuum leaks. I even tried plugging and disabling all vacuum ports including the brake booster... no change.

MAP sensor reading is on point, 14.7psi with the engine off, ~5psi idling.

My next check was to make sure the fuel inertial cutoff switch wasn't faulty. I pulled it from the car, tripped it manually and did a resistance check on it. Reset. All good.

I can only assume the MAF sensor is working fine because the last time this happened I tried replacing it and it had no effect.

Ignition on, I have strong B+ power on the brown fuel pump relay wire going into the REM indicating that the fuel pump relay in the rear distribution block is working properly. I also have a solid 12V at the Red / Yellow wires at the fuel pump under the seat when the no start condition is present.

Engine coolant temperature sensor and Intake Temperature scan tool values match outside temperature during cold start so the computer should be mapping the correct AF ratio for a cold weather start.

Fuel rail pressure shows ~47psi.

I haven't specifically checked for spark but when the car starts it runs without missing it just runs with the computer insisting it is VERY lean. Quick shot of starting fluid in the intake gets it going which tells me spark is present.

Compression check on two cylinders shows ~140psi cold cranking after the cylinders were thoroughly washed with fuel on a weak battery so I don't think it's a compression issue.

Due to the presence of the P1338 code I ordered a new fuel pump but I'm giving that a 50/50 chance of solving the problem because I can't see anything wrong with the rail pressure.

What am I missing?

Makes absolutely no sense. I've got spark, fuel and compression but the thing won't run.

 

Go for a drive to get engine hot then park and:
1. what are fuel trims at idle?
2. if you rev to about 2500 and let them settle a bit what are they then?

What are the OBD fuel pressures in each case?

 

Trims are absolutely maxed out at idle with LT 23.9% both banks, ST 25% both banks. Revving and holding ~2500 RPM the LT trim drops to 12% ST runs close to 0%. It absolutely behaves like a vacuum leak. I'm starting to suspect a leak at the seals between the aluminum intake spacers and the plastic upper intake plenum. It doesn't look like Jaguar sells a service seal set for that interface but Ford references a part for that seal for the 2005 Lincoln LS 3.9. Last night out of desperation I sprayed some brake parts cleaner around the manifold while it idled and found that the engine surged when I sprayed that seam. I think I need to pull the intake and replace every single gasket. I was afraid to build more than ~2 or 3 psi pressure during my smoke test because I didn't want to blow out aging seals but under vacuum those seals are seeing -5 to -15psi so the smoke test I performed may not have caught the leaks in action, I was probably too cautious.

I'm going to order all of the intake gaskets and do a full re-seal and see how it pans out.

 

Due to the fact that I'm desperate to keep this car running as my daily driver I'm not fooling around. Here is what I've ordered to attack this issue:

Already Installed:
New Battery - Bosch AGM

On Order:
Brand New Fuel Sender, Pump, Strainer and Crossover Pipes
Fuel Filter
Crankshaft Position Sensor
Lower Intake Gaskets
Upper Intake Gaskets
Rear Intake Gasket
Front Intake Gasket
Fuel Injector O-Rings (Upper & Lower)
EGR Pipe Gaskets
EGR Base Gaskets
Throttle Body Gasket
MAP Sensor
Aux Coolant Pump (Unrelated Coolant Leak Issue)
Coolant Reservoir Lower Hose (Unrelated Coolant Leak Issue)
Coolant Reservoir Upper Return Hose (Unrelated Coolant Leak Issue)
Sunroof Rebuild Kit (Destroyed Mechanism Trying to Clear Ice)

Tools Purchased:
Fuel Tank Sender Lock Ring Removal Tool
Actron Fuel Pressure Test Kit
Recessed Plug Inline Spark Tester

I'll be sure to fire it up and run diag tests after intake rebuild and fuel pump install so I can do a comparison to see which service makes the biggest difference.

 

P0171 is usually an air leak and it sounds like you found it!

 

Unfortunately I believe I have two separate problems going on. What I've discovered using an inline spark tester is that when the engine is cranking without starting I have NO spark. As soon as spark appears the engine starts normally but idle's rough with lean codes on both banks. Further testing reveals that when I have no spark I've got good 12V power to the coil plug. The ignition relay seems to be working fine and the fuse is not blown. The ECM is simply not commanding spark or the ECM ground is faulty. According to the technical literature, the fact that the starter is cranking and the security light is not blinking means that we can rule out PATS anti-theft issues. I've gone ahead an torn down the intake manifold because I know from other testing that the gaskets are perished. My hope is that the intake rebuild will resolve my poor idle and lean code issue. I'll replace the crank sensor and check the ECM ground during re-assembly. If I'm still experiencing a crank with no spark after all of this work I'll have to start digging into the harness, I may have an intermittent short or open circuit. This may require some serious diagnostic work involving a scope.

In the mean time I bought a 2010 Lincoln Town Car because I had to come to terms with the fact that the Jag can't be my daily driver any longer. My wife drives our 2013 Lincoln Navigator and I lost my 09 Town Car to an accident six months ago so I decided to spring for a newer TC and resolve to drive the Jag whenever it is running well.

 

The CKP would be a fair bet, because as you say PATS is happy.

 

Also 47 psi seems a bit low, it should be 55psi.

Possibly fuel pump is failing?

 

I had a similar issue with my 2004 XJ VDP and finally pinpointed it to leaking VVT seals (~$12 each). These seals are very easy to change and if they are leaking, you can actually feel the air escaping from the seals. I had changed all the hoses until I found these leaks and it completely solved my cold weather starting issue. The seals get hard and shrink when below freezing and that is what makes the leak so pronounced. I wish I found that first because I don't think the other hoses were leaking and they are not cheap. Good Luck!

 

I've rebuilt the whole intake with new seals and I've replaced all of the o-rings on the various vacuum and emissions hoses. I'm not sure what you mean by VVT seals. Are you talking about where the VVT solenoids penetrate the valve covers??

 

Yes it’s the seal around the solenoids, black rings about 1 inch in diameter. They pop right off. Need to unplug solenoid and they slip right off and pop right back on. No tools are needed although I used a flat blade screwdriver to pop them off. Good Luck.

 

Excellent Tip! Thanks! I'll check them for leaks when I get the intake work finished. I'm still working through the intake reseal project so I need to get this job wrapped up before starting any additional tasks. I'd like to fire up the engine and see how the fuel trims look after the intake work is finished. Then I can start looking at additional seals.

 

I finished the intake reseal job and the fuel trims are drastically improved but the crank / no start condition is still present. Lean codes are gone. I replaced the crank sensor, the old one looked brand new, no rear main leaks or any contamination at all. Does anyone have any other ideas besides detailed testing of the harness? I can't think of anything else that would prevent the ECU from commanding spark. Even if I had a bad cam sensor I would think that the ECU would still command spark and attempt to start. I'm really up against the ropes on this problem. The only way to get it started is to hook up jumper cables and just crank it over and over again for 10 minutes or more. The ECU just refuses to command spark. After the car warms up and reaches normal operating temp it will start reliably every time the key is turned. The problem only happens when it is dead cold after sitting overnight.

 

This weekend I plan to remove the cowl and dig down to the ECU harness connector. I'll use some piercing probes to verify good power and ground on the ECU at all of the pins involved and to check the wires for the crank sensor. So far all I've noticed is that the RPM signal on the scantool seems to flatline while cranking. My AutoEnginuity scantool software doesn't seem to give me a raw CKP output but the ECU calculates RPM directly from the sensor so the two should be linked. Unfortunately my oscilloscope is in storage in Arizona.

 

I'd avoid piercing insulation as it tends to lead to corrosion and later on failures.

 

I'll do my best to probe the connectors to avoid piercing wires but I'm out of options. Now that the weather has warmed about 10 degrees the car starts flawlessly every time. I'm going to make sure it starts normally tonight and then I'll unplug the fuel pump and watch to see if I get a consistent RPM reading on the scantool while the engine cranks. If I do then that just offers more evidence that the problem is the CKP signal because when the weather was very cold and it refused to command spark I could see that the RPM signal was spotty while cranking.

The bolt that holds the ECU main connector in place is keyed for a security torx T-25 bit. Of course I only had T-20 and T-30 security bits in my collection so I had to track down a T-25 yesterday. Now that I have the bit I'll separate the ECU connector and check the harness for pinch points. I can already see one place already that looks suspicious but the harness is frozen in position so I can't investigate without disconnecting the ECU.

I'm also going to unplug both cam position sensors and try starting the car. If it fires and starts without the cam signals then I can rule out CMP issues.

According to the electrical diagram there's no way I can have 12V on the coil connectors if the coil ignition relay isn't working.

 

*** For the record the ECU bolt is NOT a security T-25, it's actually a 5 point Security Torx Plus, probably 27IPR or 30IPR. In any event, now it is a mangled mess and has been replaced with a hex bolt.

As I suspected the car started fine last night. I pulled the electrical connector on the fuel pump and let it stall out. Then I tried restarting with the scantool plugged in and I could see a very consistent 150 RPM or so from the starter turning the engine. When the car has a hard time starting in cold weather I don't see an RPM signal on my scantool or if I do it is very flaky.

I'm extremely happy that all of the fuel trims are now settled near zero! The intake reseal work has certainly resolved the lean code issue.

I've now removed the shroud from the ECU harness connector and exposed all of the wires so I should be ready to do some probing of the pins. Last night I spent a lot of time jiggling harnesses with the scantool plugged in to see if I could replicate the fault and get the crank signal to drop out or change abruptly. No luck of course.

Tonight I'm going to jack the car up and trace the CKP wires all the way back to the ECU. I'll try to get a visual on the whole harness run and look for any suspect pinch points. Then I'll do a voltage / ground / resistance check on both wires with the ECU and CKP disconnected.

My concern is that the ECU itself has an issue. The problem occurs just below 32F at the freezing point of water. I keep expecting to find evidence of moisture contamination but no such luck. All connectors look clean and very dry. The ECU main connector looked perfect inside and out.

I wonder if the ECU got wet in the dash somehow? Perhaps I should remove it and throw it in the freezer for a few hours to see if it will start the car after being chilled.

 

I'm loving this thread. My 04 XJR has these issues (lean banks, fuel smell when warming up, hesitation) and I'm wondering where to begin. You're approach is very thorough, giving me ideas on where to start. Thanks for your work and posting!

Brad

 

Fuel smell suggests a leak somewhere between tank and engine and is likely the cause of the codes. Start at tank seals.

 

Fuel is a good suggestion but I've already completely ruled out any major problems with the fuel system. It's essentially narrowed down to the CKP signal at this point. I can clearly see loss of the crank signal on my scantool when the engine refuses to start and I know I have no spark at that point.

I've had a really busy couple weeks at work and I haven't really had time to do much with it. I ordered a new CKP harness connector last week. I'm going to run some new shielded cable from the CKP sensor up to the ECU harness connector and splice the new wires at the ECU to bypass the factory harness and provide a clean signal. If it starts reliably after the temporary bypass repair then I know it's a wiring issue and I'll pull the factory harness apart to do a proper replacement.

The problem is that the CKP signal during cranking is very weak to begin with. It doesn't take much "noise" to suppress the signal and prevent the ECU from commanding spark.