No throttle input and stalling in idle - no codes

[Bosnian Fiesta]

Car is a 2014 with 40k miles bought new. Stock except for RMM and shifter bushings. Daily driver, regularly maintained, adore the car.

The problem - accelerating in 3rd gear when suddenly engine bogs, car slows and RPM drops to idle. Push gas pedal - nothing happens. 2-3 seconds later throttle returns and car runs normal. Then while coasting to the next light, engine stalls, but starts back up & runs fine. Same problems happen again a handful of times over the next few days across all gears.

No CEL, no wrench light, no stored or pending codes. All live sensor data appears normal. Fluids are fine, no boost leaks. Not bad gas - I've had the same problem with 2 tanks. Power feels a bit low, but that might be paranoia.

Any ideas? I'm a capable mechanic but without a trouble code to point me in the right direction I'm left guessing, which is going to get expensive.

Happy to give more info if needed - I really appreciate the help.

 

[pirite]

id look at the pid for the pedal position sensor and see what thats reading when it happens. there should be two of them and they should start at opposite ends of a graph and cross in the middle. start there and see what you come up with.

 

[me32]

Pull both sides of the Intercooler piping. Inspect and clean any oil or dirty type fluid in them. They build up fluid over time causing weird issues. When done re tighten all intake clamps. 2014/2015 had know issues for loosen hose clamps causing boost leaks. They will not throw codes because it doesn't see a loose of boost all the time only under high boost. There is a thread with a diagram there are 11 or 12 clamps that must be re tighten. Also check your air filter and all sensors in the intake intercooler pipes.

 

[koozy]

There was a tsb or recall for 2014MY due to faulty fuel pump. There was a member with similar symptoms, post is buried somewhere here.


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[me32]

There was a tsb or recall for 2014MY due to faulty fuel pump. There was a member with similar symptoms, post is buried somewhere here.


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2015 had it too. Was a small run of bad pumps. Late 2014s and early 2015s

 

[Bosnian Fiesta]

I appreciate the input guys.

I checked the IC piping and didn't find any loose clamps or contamination. I even pulled & disassembled the sound symposer to check if it was maybe separating under boost, but it also checked out fine. I pulled the MAP sensors from both the manifold & charge pipe and both looked clean & good. Air filter is clean - replaced with OEM 5K miles ago.

The position sensors on both the pedal end and throttle body end are testing out good. They were showing ~15% when closed and 87.5% when WOT, which I thought was a problem, but apparently it's normal for the Fiesta ST.

Checked the spark plugs, just in case, but at 40k miles they looked brand new.

My build date is 07-16-2013, so I'm not in the fuel pump recall date range. Low pressure fuel pump (in tank) pressure was 118psi when priming, which seems OK. I wasn't able to check the HPFP pressure since I had removed parts and didn't start the car. Admittedly I have noticed a change in the pump noise in the last couple of weeks. The normally steady "whirr" noise has been replaced by a pulsating noise. It may just be paranoia, but I have had bad luck in the past with FPs and am acutely aware to changes in pump noise.

There are 2 issues that I did find with the car that might be related:

1. Weak battery - I'm still on the OEM battery which is likely from mid-2013. 5 years on a battery is an eternity in Florida heat. The indicator was green but electrolyte was so low that the lead inside was exposed and badly sulfated. So maybe weak voltage or current from the battery was causing the sensors to freak out. I'll get the battery tested and if necessary will replace & clean up the grounds.

2. EVAP system - The vapor canister & vent solenoid checked out OK and there were no blockages in the lines, but the purge valve was leaking slightly in the closed position. That explains my "stalling after fillup" issue but also maybe excess air in the engine/vacuum in the tank was causing a vapor lock condition that caused fuel pressure to drop off.

I'll be replacing the EVAP canister, vent solenoid, and purge valve just in case, and I'll be putting a fresh battery in the car. If that doesn't sort it out I might move on to the in-tank fuel pump, which may be a dealer job since it's still under warranty.

 

[koozy]

fuel priming is under different circumstances than when the fuel pump is hot after some time and under load. If you have an accessport I think you could log the fuel pump and see what it's doing.

Accessport shows voltage, so if something wonky was happening with the battery power you'd see it in the voltage reading and can be logged. Try topping off the battery with distilled water and top of the charge, though it's performance and life have been compromised with all the sulfate. http://www.fiestastforum.com/forum/threads/17078-Battery-Maintenance

Accessport seems like a good tool to have if you don't have one.

 

[Bosnian Fiesta]

Thanks for the info, koozy. I don't have an AP but I use an Autel MaxiCOM scanner to monitor the various sensor readings so I get live data from almost all the engine sensors.

I am starting to think the LPFP in the tank is the culprit. The intermittent nature of the issue plus the change in pump noise are telling, and I'm sure the long-term failure of the purge valve pulling vacuum on the tank didn't help. It looks like there have been a fair few Focus ST & Fiesta ST owners who have had similar problems that ended up being traced to bad pumps. A lot of them right around the 40k mile mark, which I just ticked over last week.

The OEM LPFP is cheap enough that I just ordered one and will put it in myself. When I install that I'll have basically an all-new EVAP system (canister, vent solenoid, purge valve) and a new pump, so if the problem comes back it's likely to be either a problem with the HPFP or something with the throttle actuator system.

I've already refilled the battery & repaired it with my desulfating charger. The cells look better, but are still somewhat sulfated so it may be beyond repair. Before maintaining it, it was showing 12.0V at rest and the negative terminal was badly corroded, which usually signals undercharging. The corrosion covered the Battery Management System sensor on the negative terminal which may have caused bad signals. After repair I have it sitting at 12.8V at rest and holding over the last 24 hours.

Upon closer inspection, it looks like there is a small crack at the base of the negative battery post that's letting gases vent directly onto the negative terminal, causing the corrosion. Probably due to overtightening of the clamp. I'll leave the battery in for the next couple of weeks, but odds are it's not long for this world.

 

[Intuit]

Do coil on plugs always set misfire codes? If not, consider testing them.

 

[Bosnian Fiesta]

90% of the time they do, but this didn't feel like a miss. You know that sudden slowdown jolt you feel when you hit the fuel cutoff at the rev limiter? It felt like that, only at 3k RPM and partial throttle.

I did get the new vapor canister delivered last night. It's identical to the old one, but weighs 150g (5 oz) less, which makes me think there was fuel contamination. Still waiting on the new purge valve & fuel pump to complete reassembly.

 

[Bosnian Fiesta]

Finally got the car buttoned up. New low pressure (in tank) fuel pump, EVAP canister, purge valve, vent solenoid, and battery.

Started the car, ran fine for 20-30 seconds, but as soon as the RPM dropped to idle the problem returned worse than before. Stalling out of idle & refusing to raise RPM. Serious bogging when I gave it throttle. So the throttle actuators worked, but lack of fuel meant RPMs wouldn't increase.

Luckily this time the ECU set a code. P0087 - fuel rail pressure too low. FRP sensor tested OK, so I went ahead and replaced the high pressure fuel pump. 100 miles later and the car is running well. Seems like the HPFP has been going bad for a while, because it feels like I made some top-end power back. Fuel Rail Pressures test @ ~600 in idle and 2200+ @ WOT, seemingly within spec.

The HPFP is a totally welded unit so there's no easy way to easily disassemble it to find the cause of failure. If I had to guess I'd say heat. VW/Audi uses a similar HPFP design and their failures are typically related to a sheared piston or seized cam follower. Neither were the case here.

The HPFP sits at the back of the engine directly above the turbo & catalytic converter. Probably the hottest part of the engine bay. On top of that, Ford decided to wrap it in a thick, dense foam insulation (probably to control noise) and then to finish the bake capped it with the ST engine cover. I also city drive this thing in FL in the summer. This thing must get pretty toasty.

HPFP failure looks to be an increasingly common problem with the EcoBoost motors, particularly with F150s. And most of them had symptoms similar to mine. Given how simple they are to replace, it might not be a bad thing to have for your spare parts box if you race or track the car.

 

[koozy]

Did you happen to note what the FRP was before changing the HPFP with the Autel MaxiCOM scanner? wondering how the HPFP eluded detection.

 

[Bosnian Fiesta]

Honestly I never did the “before” data logging. As soon as the issues started I just put the car up on jacks & started pulling parts. It was an intermittent fault and I didn’t feel safe driving it around until it happened again. Not the ideal way to go about it because you end up throwing parts at it, but I’m an engineer and after 5 years of doing nothing but oil changes on it it kinda felt good to dig in and get a feel for the car.

I did have the scanner hooked up after replacing the LPFP (but before the HPFP). And my FRP in cold idle was between 1000-1500, which makes sense for cold starts since it needs to run rich, but as soon as the idle settled down & it started bogging FRP dropped to the 70s. That means that either the HPFP was bad, or the FRP sensor was bad and the PCM was deactivating the HPFP.

I did a cursory check of the FRP sensor’s signal wire and it looked like it was ok, so I took a gamble and replaced the HPFP which seemed to resolve the problem.

I borrowed the Ultra-Gauge from my Land Rover (its like a digital multi-gauge that displays like 65+ gauges & mounts to the windshield) so now I’ve got a constant eye on FRP, fuel trims, and throttle position so that if the problem comes back I’ll know pretty quickly what went wrong.

 

[koozy]

Glad you got it sorted out and enjoying the process of getting acquainted with the car. Good to know it eventually threw a code.


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[Bosnian Fiesta]

Thanks man. The car is surprisingly easy to wrench on - not much worse than EK/EM Civics I got used to in college. Parts are cheap too, so that's a good sign for long-term ownership. The HPFP cost $283 new from Ford. BMW uses an almost identical design that's like $1,100.

Side note - do you know if the USDM Fiesta ST uses a fuel pump driver/controller module? A lot of the other EcoBoost models use it and the fuel system parts diagram shows it (#9D370), but it's not actually listed on the parts/price list.

 

[koozy]

Side note - do you know if the USDM Fiesta ST uses a fuel pump driver/controller module? A lot of the other EcoBoost models use it and the fuel system parts diagram shows it (#9D370), but it's not actually listed on the parts/price list.

I don't have my laptop with Accesstuner Race to see if there are tables for it, but I think I recall seeing tables for high pressure, which you can make changes to. I would be surprised if it didn't have a driver/controller. This ECU seems pretty robust. I'm not surprised everything is not listed. I found that out with the 2014 fuel line, which is different from 2016 on. It is available as an assembly and not individually.

 

[Bosnian Fiesta]

Well, shit - 2 days later and it started again. Quick drive out to the beach for lunch and it stalled like 4 times, same as before. Luckily I managed to pull over safely each time and it started right back up.

Code logged is P0087 - Fuel Rail/System Pressure Too Low. Pretty extensive web search yielded almost no results for the Fiesta.

Back to the drawing board. I'm looking at either bad fuel pressure sensor, bad fuel pump driver module, leaky injector, or any number of other problems. I'm not the one to fold and take it to a dealer, but that may be my final option.

 

[koozy]

I know you refreshed the battery, but do you have another known good battery you could throw in there that would fit just to test it out? The foundation for all electronics on the car is a good power source, I think that needs to be confirmed. Perhaps also try re-seating the ECU harnesses.

 

[Bosnian Fiesta]

So funny you should mention that.

The car ran great all Monday & Tuesday. Tuesday night I took it to a buddy's shop to get the tint replaced. We kept the ignition in the "ON" position so we could raise & lower windows and after a couple hours the battery went dead. Like no lights on dead.

Put it on a slow charge and after a 2 hours it read 12.9V and we tried to start it. Dash lights came on as normal, but no start. Sync came on showed the "Sync is performing regularly scheduled maintenance" message, which it does from time to time. When it finally booted, I got a notification that said "Press clutch AND BRAKE to start the engine". I'd never seen that before, just the "press clutch" warning. Sure enough, it fired right up and I took it home. Ran great.

Started up fine Wednesday morning. Ran great during my 30-min commute. Started fine on the way to lunch too, but in the 15 minutes it took me to get there, it stalled 4 times and threw the P0087 code. Each time it fired right back up normally. Started up fine after work too and no problems on the drive home.

When I got home, I got the car up on stands again and started my (fruitless) search for the fuel pump driver module. I couldn't find it, so I switched my attention to the FRP sensor. I let the fuel system get up to pressure (600psi), then killed the motor to see if the pressure would hold. It did, which eliminated a leaky injector.

I then pulled the FRP sensor and primed the system with the LP pump thinking that maybe I had water or sludge in the gas and that I could flush it out thru the FRP sensor hole. Then I'd reinstall the FRPS and start the car to see how it built pressure and if there was any differences in pressure readings. I must have started & shut the car off 8-10 times during this process. Didn't find anything wrong with the FRPS or the gas.

Then I pulled the battery & took it to Autozone for testing, just in case. Test came back "GOOD". 12.5V @ 86% charge. I put the battery back in the car and it started up again just fine. Left the car for the night.

This morning I step out of the house, push the unlock button - and nothing. I manually unlock the door, try to start it and literally nothing. All dash lights dead. Pop the hood & measure the voltage at the battery - 4.4V. Doornail dead. What happened to it between 9pm last night and 7am this morning we shall never know.

Needless to say, just got back from picking up a fresh battery. I'll install it tonight and see what happens over the next few days. I'm still not convinced that it was JUST the battery causing the problems, but given its behavior the last couple nights there's no way it was healthy.

 

[koozy]

Hopefully the new battery does the trick. How are your testing/measuring fuel pressure?