Ford Repair Questions? Ask a Mechanic for Answers ASAP
Thanks for the question.
What have you done or checked so far?
How many miles on the van?
1. We pulled the trouble codes with diy scantool (actron)
2. Fuel trim looked a little high (compared to my Benz)
3. TPS didn't seem smoothly proportional to pedal position
2. On a scale of 1-10 our vacuum leak search so far rates a 4. No obvious vacuum leaks.
3.Cleared the codes which returned after about 10 miles.
There was little obviously wrong outside of the MIL - ok idle, reasonable power
After our search car started to stall at stop signs. If you drop it into nuetral it'll
continue to run. This suggested we disturbed a vacuum leak. Further search brought no joy.
The engine is V8 5.4L
We purchased this van about 30,000 trouble free miles ago. Routine maintenance is
all that we've done.
I would make sure that there is no vacuum leak on the PCV hose. This is a common leak. Start at the valve and work your way all the way back to where it plugs into the intake. Replace if needed.
It could be a dirty MAF sensor. Clean MAF sensor wire with brake cleaner. The MAF sensor is located near the air filter element. The wires are exposed to the air flow to the engine. Unplug battery for 15 minutes to rest PCM and road test for any changes.The MAF sensor is near the air cleaner box.
It is possible that you have a fuel delivery problem. You will need to check the fuel pressure with a gauge and hose long enough to drive and watch what the fuel pressure is doing especially under a load. Let me know what the pressure reading is. Could be a bad fuel filter or even a weak faulty fuel pump. If that is the case, try replacing fuel filter first, if that doesn't work replace fuel pump.
On the PCV: We heard a rattle in the valve, changed the valve and the rattle stopped;
no immediate effect on the problem. The hose is in a heat shield, which we haven't removed yet, what we can see is noticeably heat deteriorated - I guess that's next. Any comments on the rattle?
We have CRC MAF cleaner (I just went through a similar excercise with my Benz) We'll use that. I'm told that MAF cleaner has limited value - what do you think? Preliminary visual inspection of MAF showed a clean condition.
Where on the fuel rails is the test fitting? We've been going to our local autozone - do you have a suggestion about what pressure tester to buy? Does the pressure regulator vary the rail pressure or is it constant? This test is new to me - haven't done it before.
Yes, look under the heat shield of the pcv hose. It will have holes under there too. Look real close. Very common issue on these engines. The rattle really means nothing.
Cleaning the MAF sensor with brake cleaner works great for sometime.
The fuel test fitting is on the fuel rail, it looks like a tire schrader valve. The fuel pressure will be a constant around 28-39 psi then when you goose it, the pressure should go up a little. You will want to drive with the gauge on it.
Any fuel pressure tester 0-100 psi will be fine.
Why sure I will!!
Great. I'll hit the accept button. This is my third outing with Just Answer. Each of the previous were very satisfactory. One was a problem with my marine outboard. My expert sent me down the right path. The second was a fairly complex problem with my Mercedes; multiple failures; MAF, fuel injector, and an ecu shutdown of the pulse to the misfiring cylinder. I tortured Paul, the Mercedes expert for a week until we succeeded.
He got a major bonus for sticking to it for the whole ordeal and coming up with the crucial info. By the way can't I reset the PCM with my scan tool - I already got the MIL
light to go out with it. What does PCM stand for - it's ECU (electronic control unit) on the Benz.
The best way to reset the PCM(Powertrain Control Module) is to unplug the battery for about 15 minutes.
Hello Ford Tech,
Just to let you know - we're still in process on this problem. The truck is with my foreman - (we're a construction Co.) and he won't be able to change out the PCV
hose this weekend. We'll rate the interaction and pay the fair bonus after we get success. By the way what's your name?
Let me know how it goes.
Things are getting worse instead of better. The truck stopped responding properly
to the gas pedal. When you lift your foot off the pedal the engine does not slow down
for 10 or 15 seconds. We changed out the PCV hose and disconnected the battery
as advised. The light came back on. There's clearly some issue with the throttle.
When I put the scan tool on the truck last Fri (before the new problem with the throttle)
I noticed that the TPS values were not proportional to the accelerator pedal position the way they are on my car. Could we be having problems with the throttle position sensor or is there some other explanation that fits these symptoms?
What do you mean about the TPS, what is it doing?
Well, on my car when you depress the accelerator the values on the scan tool for the throttle position sensor increase smoothly as the pedal goes down. On the truck this wasn't the case. On fri when I had the scan tool on the truck I didn't pay a lot of attention
to the TPS values - it didn't seem that they were related to the DTC codes we were seeing. Remember, my foreman has the truck. He reported to me this problem started this weekend - where when you lift your foot off the accelerator the engine does not slow down for 10 - 15 seconds. He replaced the PCV hose that appeared deteriorated then disconnected the battery. The MIL lamp came on again. He doesn't have the scan tool so we don't know right now if the car is showng the same DTC codes as before which were PO171 and PO174 (lean condition on both banks of cylinders). But we do know that the truck is not responding properly to the accelerator pedal.
At this point I think we need to pull codes again. It is really easy to disconnect something while installing the PCV hose assembly. It sounds like the TPS is disconnected to me.
We'll get the scantool to the truck tomorrow. I don't think that something was accidentally disconnected; the problem with the engine not slowing down started before the changeout of the PCV hose. The order of events is as follows:
1.The trucks MIL lamp went on - no driveability problems
2. Scan tool was connected and showed PO171 and PO171 (lean condition both sides)
3. We used the scan tool to erase the codes and turn the MIL light off
4. My foreman took the truck home. On the way home the MIL light went back on. A few
miles later the problem started with the engine not slowing down properly when the
pedal was lifted.
5. My foreman changed out the PCV hose which was deteriorated and may or may not
have had a vacuum leak. He disconnected the battery but the MIL light went back
Did you clean the MAF sensor?
Ok, just come back to this post.
On thinking about this it doesn't seem that either a vacuum leak, or a bad MAF, or low fuel pressure could account for the engine running on. Although these three items could explain PO171 and PO174 the engine running on seems to be a different sort of problem. Couldn't a bad TPS sensor account for all the problems; the codes and the
engine running on?
Yes it is possible. But instead of guessing, you need to get rid of these codes first. And we need to look at the TPS volt pattern on DCL display to see what the PCM is seeing.
I have a multimeter and I have and actron scan tool. The scan tool only reads out the
the throttle position in % of throttle opening. If the sensor changeout is not too expensive or difficult I'd lean toward buying a new one and seeing if that worked.
Ok, sounds like a plan.
Try getting a Ford dealer part only if you can. I don't trust aftermarkets?
Is the TPS mounted on the end of the throttle butterfly shaft?
Yes, it is a 3 wire sensor.
Let you know what happened tomorrow afternoon.
Ok, sounds good.
Hi Ford Guy,
Mostly we have automotive joy today ( with a small twist). On the theory that a bad TPS
was the only explanation that fit all the symptoms we changed out the TP sensor.
The symptoms were PO171 and PO174 ( lean in both banks) and also we had the
problem of the revs not coming down for about 10-15 seconds after letting up on the throttle. After changing out the TPS we cleared the codes and started the engine.
At first we were disappointed - the problem with the engine not slowing down was still with us. We expected to see the codes come back after 2-3 miles of driving. That's what happened the last time we cleared the codes for the PCV hose changeout. But they didn't come back. They didn't come back after about a 20 mile test. The problem with the engine not slowing down properly is still with us. We have no MIL light. And that's where we're at now. We'd like to fix the problem with engine slow down but the truck is quite driveable. The worst effect is that you feel the engine somewhat resisting a slowdown at stop signs and lights. Any ideas on what to do about this? I guess in a way we're a little lucky for this last problem otherwise todays work would have been more hunting for vacuum leaks and testing for low fuel presssure. - Allen
Try unplugging the IAC (idle air control) This controls idle functions and dashpot functions. This is a solenoid on the backside of the throttlebody area. Looks like the pic below.