I recently bought a U Haul box truck with 189K 6.8 V10. When I bought the truck it would start and idle but if you tried to throttle up it would die. I have replaced the PCV and connecting hoses, fuel pressure reg. and cleaned the MAF sensor {it was replaced at 180K with the O2 sensors, fuel pump, fuel pressure sensor.} My fuel pressure is 30lbs at idle with FPR disconnected & 35 connected half throttle fuel pressure is 40lbs connected. When warm it will throttle up to half throttle but runs like sh@& getting there. The O2 sensor voltage was .32 - .75 bank 1 & .03 on bank 2 with no change under load. after changing the PCV bank 2 volts came into specs but both still read lean and my Genysis scan tool reads 0171 & 0174 lean burn both banks with a P1000 drive cycle code. The guys at U Hual said they tried Disconnecting the CAT and had no change in performance. I have made minor improvements in it's ability to run but it still is not drivable. I am A.S.E. certified in engine repair and been in the trade 38 years but I am stumped. Any I mean ANY help would be greatly appreciated. I intend to use the truck for my mobile auto repair business.

 

could it be a bad intake gasket? I believe it is more of a problem with the 5.4 due to the plastic manifold. Are the plugs/boots/ wires pretty new too?

 

What year is the V-10? Have you checked the IAC (if a 2V engine)?

 

The numbers that you posted would certainly indicate a probable vacuum leak (as opposed to a fuel delivery problem). The P1000 code indicates that the codes were cleared and you do not have enough drive cycles for the monitors to complete. After some more drive cycles, more codes may set to give better direction to the problem. You should be able to look at fuel trim numbers at idle and at about 3000 RPM. If the fuel trim improves at higher RPM, then you almost certainly have a vacuum leak somewhere. Don't forget to check the brake booster valve. You can check the injector waveforms to be sure that they are functioning properly. A sticking injector (closed) could cause your symptoms. You could also do an injector balance test. When you check the fuel pressure during a snap throttle, does the fuel pressure increase some? It is critical that it does NOT drop during the throttle snap. It would also be interesting to see the misfire data (mode $06). Obviously something is not right. Patience and careful testing will reveal the problem. Let us know what you find.

 

DavidB -

When you say fuel trim numbers "improve" at higher rpms, can you clarify what that means? Go up? Go down? Looking at the numbers on my Torque app, I've always wondered what they mean, and how I can use them in diagnostics.

/thread jack. I now return you to your regularly scheduled thread.

 

Normally, you want the fuel trim to be as near zero as possible. Usually, a number within +/- 10 per cent is considered O.K. When you have a lean condition, noted by the trouble codes posted above, the fuel trim command will increase to compensate. With a bad lean condition, you might see ST and LT fuel trim numbers as high as +25 to +30 percent. At higher RPMs, the manifold vacuum gets a lot lower than at idle. If this causes the lean condition to be less, i.e. the fuel trim numbers come down, then you likely have a vacuum leak. If, at higher RPM, the fuel trim numbers get worse, go more positive, you likely have a fuel delivery problem, i.e. fuel pump, fuel filter, fuel pressure regulator, or a Mass Air Flow problem, i.e. dirty/faulty MAF sensor, faulty/dirty air filter, etc.

 

i will look further into the vacuum leak issue and let you know what I find. Thanaks

 

This is awesome! Thanks for the info!

 

Although the U Haul mechanics "said they disconnected the catalytic converter", I would also do it myself just for that knowledge .

DavidB, this is excellent information,, that should be in the stickys.

 

Good Morning fellow Ford enthusiasts. The V10 nightmare continues for me. I have don extensive vacuum leak checking and found none. After further scan tool testing I found the engine coolant temp. sensor reading 104 after 45 min of idle and some limited load throttle. testing revealed the ECU was not reading the sensor all though proper signal was flowing to it. Replace ECU it now reads proper engine temp but still having similar problem. Injector pulse is now at 195.3 KOEO (will not run presently) and short term trim is 62% with electric pressure ctrl. V at 4.1. the engine starts but now will not stay running and whether or not these new numbers make a difference I am not sure. I am off to another day of testing and . Will keep you posted and Thank You for all your input and help so far. Please any new ideas are welcome and will be checking in through out the day

 

I have been doing this stuff for a long time and your numbers do not make sense to me.

What type of scanner are you using? I did not see enough evidence to replace the ECU. I have NEVER seen a ST fuel trim of 62%. I do not know what you mean by " electric pressure ctrl V".

What is the fuel pressure (using a gauge on the fuel rail)? Have you confirmed a good spark during cranking? How did you confirm/measure injector pulse? Do you have a ckp signal at the PCM input? The engine coolant temp sensor can certainly cause rough running conditions, but I have never seen one cause a no start condition.

You need to narrow down the possibilities. Verify spark, fuel, timing, compression, and air intake. (Don't forget that a plugged exhaust can mess up air intake). Once you narrow down which is incorrect/missing it will be a lot easier to find the problem/cause. A lot of people try to troubleshoot the effect instead of the cause and that can get verify confusing. Back to basics and start over.

 

Sounds like you've been busy throwing a lot of parts at this thing with little results! That's usually what happens.

A couple thoughts (okay three):

* You mentioned something about the coolant temp sensor reading low, but you were reading a low temp with a scan tool. Then you claimed to have replaced the ECU and the reading was normal. That doesn't make sense to me, because you're reading the ECU readings with the scan tool. I would believe the coolant temp sensor would be bad, but not the ECU. No, or low reading from the temp sensor causes the engine to run rich. Was there black smoke or a rich smell coming from the exhaust when you were having the erratic coolant temp readings?

* Sometimes swapping ECU or BCM's have their own individual issues. The ECU is assuming all the sensors and systems are running correctly to function themselves correctly. In the case of a used ECU, it wakes up expecting to see the last vehicle it was in. If not, and the information it's getting is bad, it won't correct for the bad information. That's why I've found replacing an ECU is the last resort.

* Rather than throwing more expensive or used parts at this, I would put it back to how you started and be a bit more systematic about troubleshooting. Get yourself a manual that covers the proper diagnostic procedure, then walk through it step by step. Chances are it's something simple. The more multiple things you change at once, the tougher you will make it on yourself. One test at a time, check it off, then put that part back and move onto the next test.

 

I wonder if this could be as simple as it has a tank of half diesel/half gas in it.

It was a uhaul after all.....

 

With the tests that he says he has done, I can't believe that he would not know that the fuel contained diesel. The numbers that he posts are not valid, including 02, fuel trim, etc. Either someone has no clue how to troubleshoot the problem, or this thread is a scam.

 

Very curious to see where this ends up. Subscribed.