Hi all, hope you are all "negative" and well in these "quarantine" times.
Sorry if this topic was already covered, I couldn't manage to find the reliable answer.

I have 2007 Fiesta ST150 with few (engine) mods:

• Pipercross Viper VF308 CAIS
• Scorpion 2.5" downpipe, but stock cat
• Scorpion 2.5" cat-back
• lightweight flywheel

Before doing some mapping, I went to log the car and it turns out that it is running too rich (15:1 at idle, around 10.5 just before redline). Generally, car feels alright, snappier with those few parts, especially in the low range.

Since I got the car (all stock, with some unshielded K&N 57i), it was very hungry (13.0 - 14L/100km or 18 - 19MPG for you imperial guys). After some fixes (chain, lambda, etc) and upgrades, it dropped to 11-12L/100km (19 - 21MPG).

What kind of AF ratio (or AFR range) should I expect from this car?
I can provide more details, if needed.

BR,
DonYenko

Hi. That is very low mpg
Mine has full exhaust, inlet and cams but the AFR at idle looks to be about 19:1 and hovers about 12 through the range (yellow line)



I wouldn't have thought any of those mods would be responsible for it really. The fuelling is as far as I know determined by the manifold pressure sensor, lambda sensors, coolant temperature and the fuel map. Perhaps something is amiss with one of them, have you checked if there are any error codes?

Some thoughts are, I know some MAF sensors can be sensitive to the oils used on aftermarket air filters, however the ST150 doesn't use a MAF.

Is the coolant running at the correct temperature? Think it's about 80 degrees C in the middle of the gauge, the thermostats can often stay open and cause the engine to run cool.

Is the air filter clean and not blocked?

Other thing could be bad injectors but I've never heard of them being an issue.

I don't know if a bad knock sensor could maybe cause rich running also.

Hi _Jimmy_

thank you for a very detailed answer.

Yes, MPG was very low since I got the car (3 years ago). A year ago, I started with replacements, one suspicious part at a time,
with some upgrades here and there. At first, it was a dirty throttle body, then PCF hose snapped, replaced quickly. Intake manifold was
checked too, but nothing seemed wrong, only gaskets were replaced, since it was off the engine. Later on, I purchased "less limiting"
rear exhaust resonator, which later turned out to be "not enough limiting" and it has been replaced with Scorpion resonated cat-back.
Also, chain has been blamed too (although, car only had about 140k km/87k mi) and replaced, tensioners too. Last year, front lambda has
been replaced and catalytic went through a cleanup.

In one period (cannot recall when exactly), coolant temp sensor has been replaced and since then, temp never goes over "middle of the gauge",
radiator has been patched up and expansion vessel (costly little sh*t) were replaced.

Air filter is few months old, Pipercross Viper VF308 (with a cold air intake hose). Last time I checked it, it still looked clean.
Since stock airbox wasn't needed anymore, I removed it and put a breather filter to the valve cover port on the back.

Not sure if my mechanic checked the behavior of knock sensor (to be honest, I didn't know that N4JB engine has a knock sensor).
Anyway, I am pushed to the wall, mechanic is out of ideas, dyno guy that tried to map the car few months back
didn't manage to push 1HP up, also said that car is running too rich.

Sorry if my english is bad.

BR,
DonYenko

Has it been checked for error codes? Sounds like you've tried a lot of things already, seems difficult to pinpoint but any error codes could give clues. I have a few more suggestions but nothing definitive unfortunately.

Has the PCV valve been checked? Apparently it can cause rich running if it's blocked.

Bit risky but would it be possible to remove the injectors and let them fire into a plastic bottle to check that they're spraying correctly?

Did it improve after the cam chain was done? I wonder if the valve timing could be the issue.

The knock sensor was just a bit of a long shot really, but yes there is one going behind the manifold near the thermostat/power steering reservoir. Could be a manifold off job though.




Here is the MAP sensor btw in the red circle (ignore the arrows)




Other than that something in the map or the ECU, do you know if the previous owner might have had a dodgy remap?

I hope you can get it sorted.

No error codes of any kind across multiple checks.

Not sure about PCV valve, when hose has been replaced, mechanic did not complain about PCV valve, so I guess it is okay.
Funny thing, I discovered that PCV hose snapped right before MOT (bloody car was idling at like 2000RPM...)

Injector test seems doable, which reminds me that OEM fuel pump died on me 6 months ago, was replaced with
(not sure about brand, must check the packaging - it is not shitty or cheapest one) slightly stronger one (same pressure, more flow?).
Only noticeable side-effect was: in 2 out of 10 startups, car fails to start. It starts in 100% of cases on second try after failure.

After chain, tensioners, front lambda and cat-back were replaced/installed, consumption changed from around 18 to around 20MPG.
A friend with stock ("khm" K&N 57i and "khm" better down-pipe ) ST150 is getting 26+ MPG during worst jams.
Valve timing has been checked 2 times, second time when chain was replaced. No complains about that.

Knock sensor is actually not that expensive, but removing intake manifold is (time consuming).
I did it already (PCV hose) and I threw so much money in the car and did so many repairs, so why not do the KS check/replacement too.

Dodgy map would be the best thing IMHO, but AFAIK, both mechanic and "map" guy told me: "map looks very default to me".
Car was measured ~141HP on wheels, during the best run, ~138HP on average, with stock air-box and "not enough limiting" rear exhaust box.
EDIT: I certainly hope that it would measure even more with adequate cat-back and CAIS.

Thank you for helping me,
DonYenko