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Discussion Starter #1
Well, i've come here for some help... i've been a lurker for a while, and only generally post on the Canadian Focus sites, but my current problem seems to have stumped everyone. Posts on FocusCanada, FocusBC, and FJ haven't gotten me anywhere... and the tech advice over here seems to be better anyways.

Yes, everytime there's a low RPM stumble, its usually attributed to the same things... DPFE, fuel system, etc... but here's my problem:

After the engine warms up, at no specific time (anywhere from 10-30 mins of driving) I get a low RPM stumble/misfire. Usually mid to full throttle, under 3000rpm, only last from half a second up to 3 seconds. Things that seem to bring it on are either idling for a long time (long red lights), or 5-10 minutes of highway driving (5th gear, 2000-3000rpm).

Before the problems start, it runs like a dream. Turning the car off for 15 or more minutes usually makes it go away for a little bit, until it starts again. To add aggrivation to it, out of nowhere, my idle has suddenly gone low and rough as well.

Generally, no codes pop up... i've gotten the odd P0171 (yes, I have the list of code definitions) and a couple of times a P300 Pending (untraceable misfire). This problem sprouted up in the middle of a road trip, after i'd already put on over 1000km in 2 days. No changes were made immediately before the trip..

My mods are in my signature, but here's what i've tried/tested so far:

- Checked for any vacuum leaks. Haven't found a single one.
- Made sure all bolts on my ported 2K manifold are tight.
- Checked for header/exhaust leaks
- Swapped IACV with a spare I have. Seems to work/regulate normally, no change to the problem.
- Replaced fuel filter
- Ran through a tank with Fuel System Cleaner
- Replaced upstream O2
- Pulled/checked plugs and wires (less than 6 months on both). No signs of problems or arcing.
- Ran over coil... no cracks, no signs of arcing, wire pack seems good (unplugged and inspected)
- Cleaned MAF, checked that wiring harness as well
- Replaced PCV, and the PCV hose (was crushed near the manifold)
- Checked TPS... less than 6 months on that as well.
- Tested Cam Position Sensor
- All fluids and oils are clean, and at the proper levels (no overfills).
- Just installed FS/SCT chip which disables EGR (was blocked off before anyways) and rear O2 delete (still running the MIL eliminator). Still no change.

I've covered 90% of the sources of any lean condition/misfire. No apparent ignition issues. Don't know if the fuel pump recall was done, but i'm not exhibiting ANY other fuel pump issues. In fact, ANY fueling issues would usually be evident from the moment you start the car, not kick in once everything is warm, at no predetermined time.

At this point, i'm at wit's end. I'm gonna try testing the block and head temp sensors, as it also seems to be temperature based. Haven't tested the thermostat, but the car is always at operating temperature for quite a while before the problems surface.

If anyone here has any other suggestions, or other things to try, i'm all ears!
 

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Sonic Mk3 Crew #03
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sounds like timing issue. I suggest getting your belts changed and your timing redone and centered. Also on that note is the chip a reflasher??? if it is and you have it on premium and your running 87 your detonating and if you advance timing at all your deffenetly going to have pinging and or misfire. It is one of the two i suggest zeroing out your timing and making sure your chip isnt what is causing it.
 

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Discussion Starter #3
I've also thought timing, but that's also one of those things that would be evident right from startup.

As for the chip, its a multi-chip. It has maps for both 87 and 94 octane, and its set to the 87 map. Regardless, the issue was there before the chip was installed.

Thinking now that its temperature based. Unplugged the head temp sensor for a little bit. Started it up, drove it for a few minutes without problem, pulled over, plugged it back in. Fan instantly kicked on, the temp gauge kicked up, and the studder came back.

Gonna try and test the thermostat. Coolant flush was done a couple of months ago, but I didn't to the t-stat at the time.
 

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Interesting well thats all i can think of i suggest getting the timing belt changed in all anyways because its not expensive and its one less thing to worry about i mean for around 50-70k miles.
 

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Discussion Starter #5 (Edited)
Hmm.... the Cluster Test Mode shows the engine temperature at 93c (about 200f). And no engine fans. Yet the thermostat needle on the dash shows normal.

Thermostat appears to be open (coolant cycling through degas tank).

Guess i'm checking my fans....
 

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Check compression!

Get a new battery.

Those are my recommendations. When I dropped my battery in my car it made it run 10% better. Might do you some jesus as well.
 

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Discussion Starter #7
One thing I have noticed, though, seems to be that the radiator fans NEVER turn on, stock program or not. They obviously work, as I managed to make them kick in while testing the cyl. head temp sensor (unplugged it, started the car, ran it for a while, pulled over when it was nice and hot). Once I plugged it back in, the temp needle worked again, the engine instantly bogged, the fan kicked in, and the stumble came back.

It appears that everything on the cooling end works... coolant cycles through the degas tank, the temp on the gauge cluster in test mode never gets above 93c (200f). Yet, the fans never come on... not while idling for a long time (could be why the idle starts fine, then kicks down super low) or even after a long highway burn... which are the 2 things that bring the stumble on.

Theory time.... those are the 2 times when the engine gets hottest and the fan would normally kick in. Since its getting warmer than it should, the ECU kicks into self-preservation mode and retards the timing/leans mixture to cool stuff off (manual says it can turn off 2 cyl at a time to do this??).

Tomorrow, i'm gonna test the fan relays (already checked all fuses). Apparently there's some resistors/rheostats on the fan shroud harness that are prone to going? Any idea where those are?

Everything else seems to work fine... temp gauge is normal, operating temp is within spec, coolant is circulated... I may replace the t-stat just to be safe, since they're so cheap and all.
 

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I know we're talking different cars here but when the timing belt on hubbys 98 ford escort went out it was like 700 to get it fixed. So kinda expensive if you ask me :)
 

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You said you went over your coil--- does that mean you did a resistance test on each of the packs, or an overall resistance check?

That's not much of a guess, but have you checked out THIS THREAD ??

It might give you some ideas. The timing belt thing was not as far off as you might think. The computer should retard timing during start up, but once the engine is up to running temperature it will go back to it's running map. Also, how does it run with the chip removed? Sure, it may not have been wrong before you left for your trip, but it may have issues now.
 

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I replaced my timing chain on my Saab last week and my intake and exhaust cams were both jumped a tooth yet the car still drove fine, it just made less power than it should. Also, at idle the rpm used to hunt and hesitate at take-off and that was as simple as cleaning my throttle body (take it off and really clean it! those additives in the fuel tank wont take out much grime), replacing my coolant temp sensor (it was still reading right but apparenty it couls still send mixed signals to the ecu), and replacev my PVC valve. $30 later and the car ran as good as new. My dad's Mustang had a problem with hesitation when gunning it above 4000 rpm and it turned out it was a defective coil pack. It wouldnt spark at night when I started it and looked for the blue arc, but as was previously mentioned you should do a resistor check.

Just my 2 cents...
 

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Discussion Starter #11
Thanks for the suggestions, everyone!

- Not the cooling system. The fans just engage at a WAY hotter temp than anything i've ever driven before. Everything works.
- Charging system is good. Newish battery, full of fluid. 'Big 3' wiring was one of the first things I did. No evident alternator problems.
- The car does the same thing on ALL programs (87/94/Stock). Also can run up to a half hour, with normal amounts of power, before kicking in. Issues with the timing belt (recently inspected) would present themselves right after the car warmed up.
- Tested the Temp Sensor... reporting the correct temps to the ECM
- PCV recently done
- Ignition problems typically address themselves at higher RPM.... ditto for a fuel pump (still gonna see if the recall was done or not).
- The throttle body is fine... recently replaced with a Steeda one (long before problems presented themselves). Intake tract is clean.

Anyone know of a way to check the Fuel Pressure Regulator and injectors?
 

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If it has a return line and a Schrader valve you can test it, if not, then it's Ford's latest greatest idea- returnless FI. The only thing I can think of is plumb a T in the fuel system to hook to a gauge. I can't believe that they would engineer a fuel system without some sort of mechanical check built in- there is no way to see if the sensor is correct.
 

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Discussion Starter #14
whynotthinkwhynot said:
check this thread too

CLICK ME CLICK ME
Already tried that one too, as my hose was collapsed near the manifold when under vacuum. Replaced both that, and the PCV valve itself.
 

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rough idle related to engine cooling system

Did you ever figure out the rough idling problem. I am having the same problem with my Focus.

In my case, the radiator fan does not come on, i get rough idle (engine temp preservation mode) though the temp gage on the instrument panel shows normal temp. Engine light has come on in this rough idle mode.

I can manually turn on the radiator fans by turning the AC on. I am able to drive without problem using AC.

I replaced the cooling fan resistor because it showed a short between the two contacts at the plug. The resistor in my other focus is open when the engine is cold.

I tested the relays, checked the fuses. I activated the relays using 12 volts across the input contacts.
 

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Discussion Starter #16
Still haven't figured it out. The problem hasn't been as bad lately, though, and I don't know why. Perhaps its because of the weather getting cooler...

Checked with Randy @ FS about the fan settings with the chip, and it DOES come on at the proper temps.... those temps are just way higher than anything else i've ever driven.
 

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I had the same sort of problem along time ago on a Chevy. It turned out to be a hairline crack on one of the plugs. The crack was not visible to the naked eye. The stumble tended to be more pronounced during wet or very humid conditions as I recall.
 

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Discussion Starter #18
Hmm. Well, everything has gone away during the past week of cool weather and rain. Got sunny again, and now its back, but worse.

Finally got around to picking up a propane cylinder and torch. Squirted around the whole intake tract, and I think I may have found the problem. The injectors on cylinders 1,3 and 4 don't seem to be fully sealed in place. A quick squirt to each injector bung on the intake manifold resulted in a jump in RPM.

Instead of pulling the whole fuel rail and trying to replace the O rings with a larger size, I've run a quick bead of high-temp silicone around the outer injector/manifold mating surface. Its curing right now, so i'll report back if this solves the problem.

Odd that this just popped up in my email with a response.... just walked in the door from laying down the silicone!
 

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Discussion Starter #19
FINALLY RESOLVED!

Feel like an idiot... it was a vacuum leak on cylinders 1 and 4.

Car finally idles exactly as it should (well, at 900rpm... thought my chip was set for 1000?), and acceleration is better than ever, no stumbling. Extra bonus was that I no longer smell my uncatalyzed exhaust (ORP) in the cabin... guessing the stink was a side effect of the lean running.

Whee! Mechanicals are done, time for body and paint! Thanks for the input and suggestions, everyone!
 
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