1991Jeep_Man

CF has proven much more value than just for the good ol' XJ. I have several friends who often ask me for help, and many times I have posted here if I was stumped. Almost always, I get my answer.

Well folks, I need some more help. This is for a 2001 Ford F-150 with the 4.2L v-6 and matching 5 speed. 4x4 if it matters.

Here's the issue. My friend said that all of sudden (Tuesday I think), his truck would buck when pulling up hills. As far as I know, the truck does fine otherwise, but when it pulls hills it bucks, or as I figure it misses. We went ahead and changed the plugs and wires. Wires looked like the factory 12 year old units, and plugs were about 30k miles old but looked slightly burned, from which I am guessing is the bad gapping. His engine calls for about .052-56 gaps. The old plugs were about .045. Anyways, I also noted after he replaced the plugs with new ones, just as he finished up, that he hadn't gapped the new plugs. They were .045 out of the box (Autolites). But since it was late, we're gonna pull them again and gap them this weekend.

So today, he goes on the road and calls me telling me the issue is still there. He has replaced the fuel filter recently, and now the plugs and wires (and no COP here, has the little coil box thing with wires running to the plugs). So, I am stumped here. He does have a CEL, but he has had for a while (I forgot what for but he told me). I'm gonna suggest he have it checked again to see if new codes have popped. In the mean time, any fuel for the brain here? Could old 02 sensors and clogged PCV valves cause mis-like symptoms?

Any help is greatly appreciated.

Sideways99

could be the rear end.. if hes done anything to that?
if its posi it MUST have friction modifier in the gear lube or it'll puke, happened to my former employers kid

Bustedknuckle

DPFE sensor.

1991Jeep_Man

As far as I know, nothing done to the rear, but I will be sure to confirm.

Interesting. To be honest, I haven't heard of that before. What does it do/ where is it? Would it be on an '01?

Thanks for the input guys!

Edit: Research is showing it is the Delta Pressure Feedback EGR sensor. Appariently when it fails, it causes the ECM to allow too much exhaust gas into the cylinder via the EGR, which can cause a lean misfire. Considering EGR's usually function at cruising speed, one could guess it would cause the issue. How would we test this?

1991Jeep_Man

Update:

Friend said today he has noticed the issue now happens when cruising/accelerating on level road as well. Still does the same when pulling hills. But afaik, nothing low RPM/Speed related. Only happens at higher speeds.

jnicewan

Any codes, particularly misfire codes? Two things I can think of are like mentioned the DPFE sensor could be reading bad causing excessive egr flow, I doubt this one though. The other thing that I have seen which can be hard to diag is the EGR ports clogging up. The EGR flow goes to 6 individual orifices in the lower intake manifold. What happens is these ports clog up with carbon and all but one or two will clog up solid. The one or two ports that dont clog will flow all the exhaust gas into that particular cylinder causing a cylinder misfire.

You might have him try unplugging the vacuum line at the EGR valve and take it for a drive and see what happens. Also the DPFE sensor is for the EGR and it is the little black sensor (may be metal) with two rubber hoses that is mounted to the EGR tube, the part number for the DPFE sensor should have a 9J460 like this " xxxx-9J460-xx " The EGR valve is right beside the throttle body on the passenger side, the DPFE should be beside the valve.

1991Jeep_Man

I saw there the DPFE sensor on his rig was. The only thing we didn't get to do was test it because we lack a voltmeter. He actually went to have his codes re-checked (he's always had a CEL, but he knew what it was for), and come to find out he also had a Camshaft sensor code. So, we got a new one and went in to replace it. Oh my Lord... the old one had basically melted and fallen apart. We had to clean the little hole out where the cam sensor sits. But we got it replaced, and he when we started it up, we noticed the truck seemed like it 'loped' at idle for a minute, then would steady out. Push the gas again, and once the revs dropped, it would lope for a minute again, then steady out.

Also, he did say that there were emissions codes as well, but he didn't tell me what they were. Idk here. When we replaced the cam sensor, we had to remove the egr, and the port behind it wasn't too bad in terms of buildup. Got everything back together solid. Could this be the DPFE sensor?

jnicewan

It could still be the DPFE sensor, if the sensor is not reading right or not reading enough EGR flow then the PCM will command more EGR flow and then the engine will basically get too much which can cause a buck/jerk type feeling. Whichever is the case if he simply unplugs the vacuum line at the EGR valve and goes for a test drive, that will at least tell him if the problem is EGR flow or not. He will also probably get a code for insufficient EGR flow by having the EGR valve unplugged.

The EGR ports I was talking about cannot be seen by removing the EGR valve, they are deeper into the lower intake where the individual intake runners for the cylinders are. The only way to access or see these is by removing the upper intake manifold. These are notorius for clogging up especially on higher mileage engines. A lot of times the ports clog up you may see EGR codes but usually only trigger misfire codes.

Here is a pic of the EGR ports, there are 6 total (one for each cylinder) This is what the lower intake manifold looks like after you remove the upper. That little round thing with the hole in it and carbon all over it, inside the squarish intake runner.

1991Jeep_Man

That little hole is the difference between flow and clogging? That wasn't very smart of a design. Personally, I think all EGR's are a cheap solution to an easily solved problem. But, automakers will do what they do. So, by disconnecting the vacuum port off of the EGR valve, that won't cause some super radical failure of any component? He's at work now, so it'd be the best time to give a try on his way home. Would it be safe to disable the EGR (unplug the vacuum) for his hour trip home? I know he'd have to plug up the vacuum hose itself. What about the EGR fitting?

Thanks again for all the help!