Hi all, new to the truck and the site, thanks for all the helpful info people have posted. First off, I know there have been many occurrences of similar symptoms and lots of posts. I think I have read them all (this site and others). But thought I'd put my list of symptoms here to see if someone can help pinpoint the problem.
Truck has 230000KM. High-ish mileage, but I bought it because all the "major" fixes have been done already (cam phasers, timing, oil pump. etc.), it's in good shape and seems to run great (mostly!).
-First problem was random seeming stalling. At slow speeds when maneuvering (like backing into a parking spot) occasionally will run very rough and stall if you don't hit the gas. This seems to happen more when hot and is corrected by putting it into neutral and revving up to 1500rpms(or so).
- Now the truck misses/surges under load at low rpms (1200-2000), holding the throttle steady, the RPMs will fluctuate up and down 200 RPMs. This always happens when cold at slow speeds. Don't notice it much at driving speed (some random hesitation when accelerating, often when shifting gears)
-Fuel economy is horrible. Mostly highway driving I get 20l/ 100km (11.7 mpg). I get a raw gas smell in the cab occasionally, but not under the hood (so far, weird)
-Idle seems very steady at 600 RPMs (in park). Starts great. Never thrown any codes.

What I've done so far:
-Cleaned MAF and throttle body. - this seemed to help the low speed stalling (I think, we'll see)
-Ordered a new TPS online. Stripped one of the screws taking the old one out. Removed throttle body again to get the TPS off. Discovered the new TPS is the wrong one! Sending it back, going to get the right one (Thinking/hoping this is the problem, but not sure. My cheap scan tool does show the TP jumping one percent (up and down) when holding throttle steady. I noticed there is no "spring return" (moves freely, no tension) on the current TPS are these ones supposed to?)
-Had some room with the throttle body off, so removed all COPs and checked plugs for tightness. All tight and the COPs and boots look good. Didn't pull any plugs, but they look brand new-I'm assuming theses were done with the other repairs)
-Dropped the spare tire to look at the Fuel Pump Module. Didn't remove it, but it "looked" fine. It has spacers, so can see underneath. Since there are spacers, does this mean it has already been upgraded from the original?
-Gonna change the fuel filter this week.
-Checked for vacuum leaks

I really like the truck. I drive a 2011 ecoboost for work and I prefer my 2006. Just need to fix these (hopefully minor) issues!

Thanks in advance for any input!

 

I would not discount the possibility that you have a bad COP or plug... or the electrical plug on the COP. Eventually it will throw a code, or you need a real time code reader to see the problem.

 

redundant post

 

Yeah, AFAIK the spacers on your FPDM mean it's been replaced.

That said, if it's a Dorman I'd be skeptical. Now, the Dorman seems well reviewed and well liked but I've learned to never trust anything electrical from them. I purchased Motorcraft for my '08 for this reason.

However I'm not certain your symptoms fall in line with a flakey FPDM, so that's probably not at the top of the list.

 

A crack in the intake manifold would certainly be an issue. Having said that, I can't see the crack you're referring to. It looks like you have a lot of oil residue build up in the throat.

 

Thanks guys for the input. Yeah @Rumble phish could be nothing, but this is the spot I was looking at:

 

I can't identify the crack either . The best test is a home made you tube smoke machine put rubber glove over throttle body intake -that really shows the vac leaks . Surging is a sign of a vac leak '
Gas smell is often a loose plug they must be torqued down 25-28 foot pounds . Trouble is a loose plug gets destroyed by blow by So you must replace that plug and boot . All plugs should have been changed to sp546's with new boots . Use a very small amount of dielectric grease on each end of boot . Clean all cop contacts . Do a hosp clean plug job .
If you have sp515's bet them out of there .

 

More great info, thanks! Did some fuel trim monitoring today and also managed to get the CEL on.

No fuel trim expert, but they all seem to be in normal range EXCEPT LTFT B2. The LTFT is 10-15 positive under load, but jumps around depending on acceleration. Which seems weird for the LT. Also seems weird to me that the ST is more stable than the LT!

Because this is only under load and only one side, I’m thinking not vacuum? Of course anything is possible.

When I was driving around slowly monitoring my scanner, rough idle returned and just about died. I left the gas alone and the CEL came on. Codes were p0300, 305, and 307.

I think that’s bank 2 on our rides? Might be getting somewhere.

Seems to me the PCM is thinking Bank2 is lean and adding fuel. And flooding.

Injectors? O2 sensors? I think the MAF would affect both sides?

 

the cylinders on the drivers side are 5-6-7-8 from front to back, so you have the drivers front, and the third one back misfire..

Missfire can be plug, coil , boot, or the harness on the coil.... Normally if it is fuel related, you will also get a fuel related code..

 

300 is Random Missfire which means multiple problems.... concentrate on the coil / electrical plug / boot on #5 and #7... and make sure you have the NEW plugs, not old style.

 

Thanks @redfishtd . I did check the plugs, all tight. Plugs and boots look new-of course doesn't mean they're working! I'll try and figure out which ones were put in.

 

Thanks @steve(ill) . Makes sense. Any idea on the fuel trim? LTFT is generally high on the same side. I will swap the coils first and see if I can get the CEL on again. Anyway to actually test them?

 

High fuel trim makes you think that an injector or two is not working... The computer sees " less fuel" being burned and trys to compensate for that......... That is a possibility that you have #5 and #7 injectors plugged... that can cause a misfire also. Swapping the injectors with other or a spare will tell you that.........Swapping coils is also a simple test for the coils.. Some more expensive code readers can give you additional real time data on performance............. I think the guys call that Mode #6.

 

Daughter had a 2006 4.6 motor with a "misfire" for a year off and on... I changed coils on the coded cylinder a couple times and seem to help, but came back later..... Finally put all new injectors in and problem gone for 2 years now... all I got for codes was 303 and 305.

 

Follow Steve’s advice, but, not trying to confuse the issue, but, with high LTFT on bank 2, you could have a an intake manifold vacuum leak on that side. The O2 sensor sees the excess oxygen from the vacuum leak and the PCM responds by increasing injector dwell time on that bank, which increases the LTFT. Since the PCM doesn’t know WHICH cylinder(s) on that bank are lean so it increases the dwell time on all bank 2 injectors. That could make the cylinder(s) with a vacuum leak run just right yet cause the cylinders without any vacuum leak go too rich and cause them to misfire (which sends MORE oxygen down to bank 2’s oxygen sensor, which increases the injector dwell time, etc,etc)

You can put your ohm meter on the COPs and measure their resistance, but that will only tell you if the COP is bad, but won’t tell you if it is good. Quickest way to test the COP (without a scope) is to move them around.