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on thin air
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Discussion Starter · #1 ·
Continuing along my path of troubleshooting....working on a funky idle.

JRSC BBK - Car idles with an odd miss. Got it on a dyno and it idles at 19 AFR. Looking at the vac readings - wobbles between 12-14 with idle miss (up this high 15 is the norm)....holds boost just fine. Gearing down a hill, it will hit 17/18 whereas 20 in norm.

So the guess is a vacuum leak. Went around the car hosing it down with spray listening for a change in idle...nada. All connections are über tight too boot. Final test was done on the by-pass actuator....

First test - disconnect vac hose, pull open by-pass, place finger over nipple on actuator and let go. By-pass closed with no problems :/ So, I then hooked up the MightyVac to the actuator and tried to vacuum the by-pass open. No dice....so it must be leaking, but I hook it up and it's working ok. SO....

Final test - Disconnect actuator, zip tie the by-pass open and plug the vac line (thereby eliminating the leaky part). Car still idles like poop and I get the same vac readings. Same odd miss. So I found a leaky part, but not my problem part.

Could the IAC be the culprit? Would it leak vacuum? Obviously it could cause an odd idle, but could it cause the car to go lean like that?

I plan on disconnecting the IAC and seeing the result. Also thinking about maybe disconnecting the TPS after that and seeing how it idles.

Any other ideas are welcome. Thanks
 

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i had a horrible idle once and it was a vac leak but it was way worse than yours my gasket was bad but yeah id check the iac and the tps both cant hurt. and is your throttle body gasket and spacer lined up right?
 

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Supercharged
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There is a free vacuum port on the back of the intake manifold. JR requires that you cap this yourself, no bid deal right? Wrong. I went down to the auto store and got a cap...Well it cracked and appeared ok but quickly replaced it with a high quality one from Jegs. Well that wasn't good enough. I ended putting another one on and a hose clamp on it. This last one has been a success. That's where I was losing vaccum and I would definitely check it out.
 

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I AM DA FOCI FANATIC
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First test - disconnect vac hose, pull open by-pass, place finger over nipple on actuator and let go. By-pass closed with no problems :/ So, I then hooked up the MightyVac to the actuator and tried to vacuum the by-pass open. No dice....so it must be leaking, but I hook it up and it's working ok. SO....

F
The by-pass opens by vac and boost. You need a positive force on one side and vac on the other. That is why that test failed.
 

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This definately sounds like a vac leak. One very common source for a vac leak is the U shaped hose on the vac canister thing that is attached to the firewall close to the snout of the blower.

The second common source for a vac leak is a pressed in nipple for a vac line on the back of the manifold, the metal nipple actually gets loose and comes out of the manifold. These were generally found upon install and were just a bad batch of manifolds and were quickly corrected.

A vac leak that I had on my car was on the PCV line. Idled rough and generally ran crappy at low RPMs. Turned out to be the oil catch can I installed had developed a leak due to some allen bolts vibrating loose.
 

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on thin air
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Discussion Starter · #6 ·
okay, update....

In checking the nipples on the back of the mani, I ended up pulling one out - tapped it back in tightly, then JB Welded it in place. All vac connections were sprayed and no leaks found...they are all zip tied/clamped tight (if a clamp fits, its clamped otherwise ziptied uber tight) I am using the revised vac set-up that Oscar posted on FJ, so both nipples on the back are being used.

Changed my PCV out and checked all the lines. Catch can had a bit of oil on the outside, so I replaced it just to be safe.


Got a hold of Oscar Jackson and asked him about testing the by-pass. According to him, I should be able to hook up a mightyvac and draw the by-pass open. It should stay open till I release the vacuum. Well, it wiggles a bit when trying to apply vacuum, but there is obviously a leak.

I disconnected the by-pass and plugged the vac line tight. I then zip tied the by-pass open....so technically, I just eliminated the vac leak. Well, it still has the same idle. So, I found a tiny leak, but not the source of my problem. I ordered a new by-pass actuator from Moss yesterday anyways (not looking forward to that project)

I then hooked everything back up and disconnected the IAC. Car died immediately and would not idle, so I guess its working....maybe not too well? Also tried the same thing for the TPS and that car idled the same until the fans kicked on and there was load on the system...then it idled like poop.

I am going to try some datalogging today to see if anything shows up. I might also order up a new IAC just for the sake of ddoing it anyways. I already have to pull the blower to get to the bypass so I might as well replace that while I am in there.

Would still appreciate feedback if any of you have it.

Thanks
 

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make sure you gasket b/w the blower and manifold is good mine was flimsy when i put t back on and did not work at all so i ordered a new one i have two new ones setting around if you wanna get one! but you may not need it
 

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If you have a vac/boost guage on your car it is pretty easy to tell if you have a vac leak. When the car is at normal operating temp, AC off, at idle (900 rpm), you should be seeing about 19 on the vac guage. If you are then look for some other problem cause it is probably not a vac leak.
 

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Discussion Starter · #10 ·
^^ yeah I have a vac guage, but up here at this elevation...it's more like 15 is the norm, lol.

Came out this morning and replaced the U-shaped line you mentioned, Pat. It was looking a bit worn. I took a piece of vacuum hose and made a shield for it as well, to protect it from rubbing on the blower.

Got under the car and checked the brake booster line, made sure all the bolts on the manifold and the four holding the blower, were snug. All hoses check out and no amount of spray anywhere is showing me a leak. Really think this is a AIC issue now. Thinking about ordering one up to be replaced when I do my by-pass actuator.

Flashing the car with 1k idle for now and will try to get some logs before the girlfriend gets here.
 

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Discussion Starter · #11 ·
bumped idle to 1k...tiny bit better. Here are the logs I took...maybe someone will catch something.

Idle Log 1 - You can see in the begining that the STFT are hanging down at .75 for a while. Then all of a sudden there is a change in the idle and they go up to 1.0 and stay there. You will also see where my fan kicks on and off. Somewhere in there is a wierd glitch in the logging...just ignore it.

Idle Log 2 - This is after the fan kicked on and off a few times. You can see the LTFT and STFT's stay right at 1.0 and at one point the fans kick on again.
 

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Discussion Starter · #13 ·
Thanks Jacob, I appreciate the offer! I think I am just going to get a new one through Mike, then do it and forget about it. It looks like you have to pull the blower to do it (?) so I only want to do this once...while I am replacing the by-pass. But cheers! Very cool of you to offer.
 

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no problem dont blame you on that one though,ive taken mine off and put it back on prolly 6 times now total im gettin good but it still aint the funnest thing! some one said they changed it with the blower on but i cuoldnt i think they might have had a zetec and it was prolly diff. but yeah the blowers most likely gotta come off the second bolt is a tight squeeze to get to. if you didnt get a new gasket and want one i can send one your way for cheap let me know.
 

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Discussion Starter · #15 ·
Well, I got a new by-pass actuator from Moss and replacing it involves pulling the blower off the manifold :/ So in the process of replacing it, I managed to snap off a TB bolt while putting it all back together. Grrrr. Tried to use a bolt extractor and the tip of the extractor snapped off in the bolt Grrr x 2 Not sure if this has ever happened to anyone before, but you cant drill the extractor...it's too hard and the bit won't bite. So I left it and sought out a machine shop to get it out proper and not mess up the blower.

I found a guy here locally that has an EDM (Electrical Discharge Machine) and had him erode the bolt out of the hole (actually didnt know that was possible, electricity FTW) So now back in biz...


  • Replaced by-pass actuator
  • Replaced vac line between actuator <--> manifold
  • Replaced PCV valve and hose from PCV to tube under coilpack
  • Removed IAC and cleaned it with TB/Intake cleaner
  • Replaced mystery U-shaped hose on plastic canister mounted to firewall near the nose of the SC and then cut rubber hose to fit around the new line to protect it

Got it all back together and fired her up. She idles nice and even at about 980rpm. Still didnt like the cold start (was in the 20s last night), but it has always been like that....just needs a lil bit of gas for a sec and it's all good.

Still need to log it for final approval, but things are definitely looking and sounding much better.


BTW - Vac leaks suck! :)
 
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