Can a bad fuel filter cause hesitation/low boost

[Ted B]

I have a 2003 mach 1 procharged, and i've been having hesitation issues, i've got new plugs, checked and ohmed all my coil packs, and just recently bought a chepo boost/vac gauge to see what i was making boost wise. I know i'm supposed to be around 8psi, however its only showing about or less than 4 psi under full load.

Could a clogged fuel filter cause hesitation, I'm sure it can, but can it cause me to have less boost?

 

[blownstang4.6]

You have a vacuum link somewhere or kinked boost line. Check your piping couples/clamps and the boost line. It could be kinked. When does the hesitation happen?

 

[Ted B]

@blownstang4.6 it happens at about 10-20% throttle, any gear. However when I go WOT it wont hesitate, but i'm only getting 3.8ish psi of boost when i should be getting 8psi. I think i need to invest in one of those smoke machines to find the leak...i've checked everything a few times and cant find anything obvious.

 

[01yellercobra]

Check your bypass valve. If it's not sealing it'll cause low boost.

 

[Ted B]

@slow984now yeah did a full rebuild on the surge valve she should be tight as a drum, but it would be worth a second look, and come to think of it, I never did check the other end of the hose that connects to the output from the supercharger.

 

[blownstang4.6]

Is it a hiccup? Like the car quickly jerks when you're cruising with light pressure on the gas pedal?

 

[da5deuce]

If you have a BAP, then check to see if the lines are properly grounded. I had the hesitation problem. Chipped some paint out of the trunk, regrounded it, and no more hesitation.

Sent from my SM-G955U using Tapatalk

 

[Ted B]

@blownstang4.6 yes any gear it can happen, I think I might have a compression issue, just had my oil changed not that long ago and now my oil looks dirty. its exactly like that almost like its not getting fuel..but ive done fuel pressure tests and compression tests both came back ok...

 

[01yellercobra]

Did the oil smell like gas?

 

[Ted B]

hard to say, almost like when its cold havent started it for a while I have to burn off shit before the car will start and stay running too.

 

[blownstang4.6]

@blownstang4.6 yes any gear it can happen, I think I might have a compression issue, just had my oil changed not that long ago and now my oil looks dirty. its exactly like that almost like its not getting fuel..but ive done fuel pressure tests and compression tests both came back ok...

Needs a tune adjustment. Injectors are shutting off and on very quickly when you're foot is barely on the throttle.

 

[blownstang4.6]

hard to say, almost like when its cold havent started it for a while I have to burn off shit before the car will start and stay running too.

Sounds like another tune issue.

 

[Ted B]

tune worked fine for 7 months...why all of a sudden now out of the blue its not working? sounds more like a mechanical or electrical part failure to me.

 

[Ted B]

ok its like 9 degrees outside haven't driven the car in a while...exhaust tips have always been black due to carbon so i never checked, but started her up let it run for a while till i had some temp, swiped my finger on the exhaust pipes...both have OIL...so i think im looking at bad piston rings...this would account for hesitation, low boost, and other issues...uhhh i just cant catch a break with this car between the tranny taking a crap and now engine issues, guess i just bought an abused car or a lemon...although i've owned 2 other new edge mustangs, and i beat the shit out of them and never had these issues. I know i broke stuff, but that was well my fault, this is not me and im sure im looking at an engine pull....more $$$$ man i need someone in my area that will help me out with this i cant fix shit in a parking lot!

 

[01yellercobra]

You've still got a few steps before deciding to pull the engine. Are you still running PCV set up? If so that could cause the oil in the tailpipes. Especially if you don't have a catch can. What plugs are you running? How confident are you in the boost gauge you bought? Plus if you really are only seeing 4psi when you're supposed to be getting 8psi it's running pig rich. The ECU doesn't know it's only seeing 4psi so it's fueling the engine like there's 8psi. That's going to leave black residue in the tail pipes.

What is the full set up? What MAF, pumps, injectors, etc. The more details the better we can help.

If it were me I'd start with a compression test and see what that shows. If it's low then move on to a leakdown. Or start with the leakdown test. If something is bad then you'll know it. If the leakdown comes back good it's time to start looking elsewhere.

When the car was tuned was the weather warmer and then you started having issues when it turned cold?

 

[Ted B]

ok so i cleaned up the PCV...and noticed both my oil cap and oil in the PCV valve itself is brownish...thats coolant contamination isn't it?

and just to be clear not brownish like slightly used oil brownish like sand brown. also i just had the oil changed like 1500 miles ago sooo yeah.

 

[Ted B]

ALSO to answer all those Q's
42lb injectors
stock fuel pump
brand new NGK TR-6s Gapped to 0.028"
Boost gauge was cheap but i highly doubt its 4lbs off...
Maf is Stock located on the pressure side of the blower, connected to a Mafia from diablo sport as not to ping out
51k miles
new transzilla TR-3650
new Mcleod Clutch and flywheel...rated at around 750hp each
I've not beaten on the car, but its had sever owners so abuse is possible
Compression test are 120psi all around...I had 2 that were 90, but i redid the tests and was able to crank out 120 psi
also did a fuel pressure test, the results are sketchy at best it was an air gauge and it was all over the place however idle was 29psi, even when it stalls out.

Car seems to run ok however right before it stalls it feel like the drop in RPM when you unplug either a injector or coil...a few revs....and its ok again.

 

[01yellercobra]

If you're not getting it warmed up and driven it'll leave a weird residue on the oil cap and PCV. It's one of the reasons people say don't just start the car and let it idle. It'll never get hot enough to burn all that crap off.

Might be worth doing a leak down on the two that initially were low. That's kind of weird that they started off low and then came up. That would make me think something is hanging.

I hope you're running a BAP with that stock pump. There's no way a stock Mach pump will keep up with boost. IMO it's best to monitor a returnless system by datalogging the PIDs pressure drop across the injectors and fuel pump duty cycle. Watching a gauge is hard as the pressure is constantly changing.

The reason I asked about when the tune was done is because sometimes when the weather is at one extreme things will get overlooked. Such as if the car is tuned in the summer chances are the cold start tables aren't really messed with it. But come cold weather when those tables are needed things will start acting up.

I calibrate gauges for a living. I've seen worse.

 

[Ted B]

car ran great for 7 months with no issues other than the trans failing on month 8. If the tune were done by a crappy shop during the summer i think there is a chance that they could have not been experienced enough to adjust the tune to work for both summer and winter. The hesitation was slightly there when it was warm, and got worse when it got colder.

 

[01yellercobra]

If there was a hesitation before I'd say the tune had issues. Was it tuned before you bought the car?