High fuel consumption, hesitation on occasion when accelerating in higher gears.

Hi there. I'm having an issue with my car using too much fuel, the mileage seems to have almost halved over the last few months, it smells rich when it starts, and tends to hesitate in 3rd/4th gear, or when hard accelerating usually up a hill. Other than that though, it starts and idles OK and generally runs fine. The car is a 2001 Ford Mondeo mk3, with the Ford Duratec 2.5l v6 24v engine (I think similar or same as the Ford Contour). I do not have any DTC's set and the MIL light is off.

It seemed to develop the problem a while back after I fixed a vacuum leak on the oil separator assembly vacuum lines. I'd had the MIL come on then and lean codes P0171 and P0174 for banks 1 & 2, but it ran OK like this though so I didn't immediately troubleshoot it but after a few weeks I heard a loud hiss when it was idling, found the leak and fixed it. MIL light went off after that, cleared the codes and they didn't come back. But not long after (maybe a month or two because I hadn't really been driving the car much), I noticed the lowered fuel mileage and it seems to have got worse lately.

The car also started misfiring at the same time I noticed the high fuel consumption (and it was quite bad at early on), I assumed it was maybe the coil/plugs/leads that were gone or going bad, which may also explain the higher fuel consumption, so I replaced all of them. This actually did seem to cure the car's hiccups for a short period but I noticed it was still hesitating in higher gears up hills. Certainly seems to do more in wet weather than dry.

Someone suggested to me recently to check the oxygen sensors on the car so I've been using Forscan on my laptop connected to the ODB port of the car to check things, but being a novice I'm not really sure what I'm looking for. The engine has three sensors on it, two upstream, one on either bank of course, and a single downstream after the main cat. Looking at the oscilloscope function of Forscan it seems the upstream sensors are at least working as they do seem to be constantly switching back and forth between lean and rich. The downstream sensor stays fairly constant after the engine starts to warm up.



From top to bottom, it's OS11, OS12, OS21, RPM, STFT1, STFT2, LTFT1 & LTFT2. That screenshot shows the first two minutes from when I started the car from cold and just left it to idle while it warmed up.



This screenshot shows it from ten minutes onwards after it had warmed up. The only thing on these graphs that I would say seems off based on my (very) limited knowledge from what I've been reading is the LTFT on bank 2 seems to be riding positive all the time, and never goes negative like the other LTFT, so I assume the problem is on bank 2.

I recorded the data while idling but I also went out for a drive in it while still recording too, hence why I added the RPM data:



This is around the twenty minute mark, driving around town. I know what I've provided is fairly limited, but I would appreciate it greatly if at least someone could give me some suggestions and pointers as to how I might go about continuing to diagnose this. Many thanks!

From the looks of the bank one sensor 2 (the one after cat) looks like it is toast but you will need to test it to confirm (unplug vac line see if it goes lean then feed propane in it to see if it goes rich after hooking vac line back up). if it still is smelling like fuel when adding propane you will need to check if fuel injectors are leaking or not closing with a fuel pressure tester. This test is done with key on engine off with fuel pressure gauge installed. You just need to see if fuel pressure is dropping past regulator pressure. If it is lift up the fuel rail with injectors and look for dripping fuel from injector nozzles. If nothing there then you will need to check fuel pressure regulator to see if it is sticking by cycling key on while watching fuel pressire which should go to 50-60 psi at first then drop to rest pressure ~45 psi (you will need to consult service manual for known good pressure) if that is good and no bleed down in pressure you will need to check injector drivers for switching ground using test light clipped to bat positive. If all injectors switch (aka light blinks) then drivers are good. This leaves th o2 sensors to blame for rich condition ( longer injector on time)

Thank you very much for the suggestions. I'll get right on it!

Hi again. I managed to get some time to try the lean/rich test on the sensors just now as suggested. I let the engine warm up for a couple of minutes until the sensors started to work, then popped a vacuum leak on the inlet manifold, which nearly stalled the engine but I managed to cap the leak enough to keep it going.



Then I tried it again with some revs.



I did the rich test too, plugged the vacuum leak then ran propane into the air intake. I couldn't quite manage to get a steady flow of propane into the intake because the valve on my propane bottle is a bit dodgy but you can see where it went rich a few times:



So, looks like the upstreams both reacted to the rich condition but the downstream didn't change much.

I will also note that I couldn't smell fuel while I was doing either test, I usually only smell it when the engine starts up anyway.

At any rate, does that downstream sensor look kaput then? I'd love it if that's all that's wrong with the thing, because that sensors actually nice and easy to get at and I do have a new spare downstream sensor I can fit.

It sure looks to me like the downstream is doing its job? :huh: Or rather, it looks like you have two healthy catalytic converters. There's a noticeable delay between you opening/closing the vacuum leak, and the downstream sensor switching. That suggests some level of oxygen storage. The test drive data also suggests there are no significant exhaust leaks between the upstream and downstream sensors.

Did Forscan list a Rear O2 Fuel Trim in the PCM data list? Probably not, given the model year, but it might be fun to check.

Did any of your previous captures show the hesitation in 3rd/4th or when accelerating hard up a hill? If not, could you get a capture of that and post it? Because your trims are pretty good, IMO. :silly: Little bit of a positive change in the long terms on acceleration? But that's not unusual on a 19 year old vehicle.

Unfortunately it doesn't have fuel trim for the rear 02 sensor, looks like you were right, car's too old for that high tech wizardry.

As for if the captures show any of the misfires, I didn't think to note when if any misfires happened when I was recording the graphs, so if they do show any I uselessly couldn't tell you where.

Annoyingly, I've been trying to get the car to misfire while recording forscans output since you posted that and I cannot for life of me get it to do it now. It's like it knows and won't play ball. I'll keep trying.

Hi guys,

Are wheels moving freely?

No suspension/trans issues?

Maybe is not related with engine.

Regards.

Wheels do run freely. and I don't think there's an issues with the transmission. Seems to change gears smooth enough and doesn't make any noise. Ultimately, the car drives just as well as it used to it just started drinking heavily.

Could it be the fuel pressure regulator?

I would say not.

Since all PID's you have posted look pretty normal.

I think we need to "expand" the search. ECT, MAT, air flow.

OK, I'll have a look see in forscan to get some graphs running for the temp sensors and MAF.

Well I had a look for temperature and MAF PIDs in forscan, there were several PIDs and I wasn't entirely sure which ones to use so I guessed, looking at it I must have missed the ECT actual reading in °F but I put the voltage reading there.

Top to bottom it's; ECT sensor voltage, IAT °F, IAT sensor voltage, MAF lb/min. Graph begins a few seconds before I started engine from cold and drove it for a while until it had warmed up.

I will add to all this that I appear to have a minor oil leak. I was under it today and noticed a few oil droplets hanging off the sump but, oddly no oil patch on the ground so presumably only leaks when the car's being driven. I couldn't see where the leak is coming from, but it seems fairly oily up around the aux pulleys so hopefully it's just an oil seal leaking.

This did make me wonder if perhaps the PCV valve has failed as I've read that can cause things like oil leaks and high fuel consumption? Typically on this engine it's hidden under the upper inlet manifold so I'd have to take it off to get an actual look at it which I'll likely end up doing over the weekend, however I was able to stick my hand under the throttle body and follow the vacuum lines back to where it connects to the PCV and it felt very oily where it connects.

As I say I think I'm going to have to bite the bullet and take the manifold off in the next few days and check on these things, but if anyone's got any pointers in the mean time I'd appreciate the input. Thanks for all the help so far by the way guys, this is as much a learning experience as it is a fault finding escapade for me.

Sorry for the late reply been busy which is a good thing for me lol. The thing i dont like is how the rear o2 returns to .83 v and stays there. So either you have an injector sticking open or a pressure regulator leaking. Possibly something else causing it to run rich

When I get a pressure gauge kit that actually has an adapter that fits the engine fuel rail's schrader valve I'll try and test it as per what you wrote in your first post. Bought what looked like a perfectly decent (all be it cheap) gauge off amazon and it has plenty of adapters, just not one for what I believe is the same sized schrader valve you'd get on a car tyre. Not exactly a great start to the weekend for me.

The innova fuel pressure tester thats sold at advanced auto will have it for ~44 bucks.

Basics High fuel consumption + misfire then first step is always do a compression test,

I don't think I'm going to be able to do any more testing myself beyond basic stuff. I haven't found a pressure tester that I can afford at the moment that looks like it'd definitely have the right adapters for this engine but hopefully I'll get one of the ones suggested or something cheaper as long as it says it'll fit sooner or later. Also today I found out about Forscan's ability to get the ECU/PCM to do a self diagnostic check. I did the 'ignition on, engine off' check, it came back with a DTC saying the IMRC was stuck closed. I did the 'ignition on engine on' test as well but it did not find any faults (not sure why the IMRC one didn't show up again). I'll have to do it again when I get a momentjust to double check, also because I frogot to write down the exact DTC that was thrown for the IMRC fault. But I suppose if the IMRC is dead and the secondaries are stuck closed that might explain the misfire/hesitation at high RPM I was and sometimes still do experienc, although currently it seems to mostly misfire on acceleration only in wet weather.

I still haven't found the time to take the manifold off to look at the fuel regulator directly with or without the prssure tester either, but based on my basic checks it doesn't even look like it has a pressure regulator, not in the traditional sense anyway - all documentation I found says it's on the fuel rail under the manifold but I can't feel it there when tracing my hand back along the fuel rail. I did cheat slightly and undo the bolts holding the manifold on (but without taking the rest of the connections off), just so I could lift it up slightly and look under it, and again couldn't see the regulator where it's supposed to be or feel it with my hand. DOesn't mean it isn't there of course as I'd only know for certain by taking the manifold off completely it seems, but having looked at various pictures of the fuel rail for this engine online it looks like there's two versions Ford used, one with a regulator where everything says it's supposed to be and one without. If this is the one without the regulator under the manifold, I've no idea therefore where the regulator actually is. Could it be part of or attached to the fuel pump instead?

As you know I changed the spark plugs earlier in the year hoping it was part of the problem, but it wasn't. I've never actually looked at the old plugs but I still have them and it occured to me I might see fouling on one or more of the old plugs potentially showing a potential culprit. But they mostly all look the same as this one:



I'm certainly not going to pretend I can say for sure they all look OK, but based on pictures I've searched for on plug condition "reading", aside from the red tan which I'm lead to believe is normal due to fuel additives, they're all fairly healthy looking (unless I'm utterly wrong but then that's why I'm posting the pics so someone can tell me as much).

The imrc valve stuck closed could be the plastic clip that holds the rod from the imrc controller broke. This is typically caused by sludge/tar like buildup on the imrc butterfly valves in intake which sticks the butterfly valves shut breaking off the clip in the process. The root cause of this happeneing is directly tied to a pcv valve failing along with a egr valve failing. The bad pcv feeds the oil into intake and egr valve feeds in the carbon soot which makes your tar in the intake. One thing to note is that when replaceing egr valve you may need to reflaten the egr mount flange that goes into intake manifold to get it to seal. Plan on spending an afternoon at minimum cleaning intake and valve runners out. Also take the sparkplugs out to avoid hydro locking engine.

Been a while since I posted but I've had a wonderfully hectic life lately, and fixing the car's been low priority.

I still haven't been able to buy a pressure tester. Just haven't had the money to spare, even for a cheap one (though all the cheap ones avail;able to me don't mention being compatible with fords specifically so I don't trust them anyway).

I saw some guy on youtube test his injectors for leaks while under pressure (but not with the engine running or doing a leak off test) just by pulling them out of the engine while still attached to the fuel rail (but unplugged from the harness) and turning the fuel pump on. So I did the same thing and none of my injectors are leaking in that way. I know that still doesn't necessarily mean I haven't got a bad injector, but I haven't got anything left in me to try and carry on testing it.

Looked at the flaps when I had the manifold off. They operate OK, and I wouldn't say there was excessive amounts of gunk or oil around them or the inlets so I suspect the pcv valve is fine. The IMRC apparently not working might just have been a fluke, or, it's suffered the common fault these duratecs have witht heir IMRCs and the PCB in the actual control unit is dead. Not really worth bothering to fix since I rarely drive the thing at high revs anyway so the secondaries rarely get to open.

Looks like I'm just going to have to admit defeat and take it to a mechanic.