car wont hold boost...please help - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 24 Old 06-06-2011, 05:00 PM Thread Starter
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car wont hold boost...please help

hey guys , i have twin turbo 5.0 stock botom end just rebuilt,trickflow heads and cam,systemax intake and 39# injectors with C&L MAF. the car has not been tuned as of yet, the problem is when i roll into the throttle and it starts to make boost around 2-3 psi the bypass valves will open and close and open and close and keep doing that until i let of the gas.i had this same issue last year with a totally stock motor and now im having it again and dont know what it can be.the weird thing is when im in 1st gear it will go and make 10psi and the car screws,every other gear it keeps opening and closing the valves...what can cause this? what should my timing be set at? do i need a timing retard at all? could it be the C&L? some guys say they are no good.
oh and im using external W/Gany help would be aprriciated. thanks- justin

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post #2 of 24 Old 06-06-2011, 05:55 PM
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where are your vacume sources for W/G and BOV? I personally wouldn't be out trying to get into boost without a tune on my car especially upwards of 10#'s

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post #3 of 24 Old 06-06-2011, 06:34 PM Thread Starter
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Vacuum for w/g is off the compressor. Vacuum for bovs is from manifold. When it was tuned last year it had the same issue.
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post #4 of 24 Old 06-06-2011, 10:04 PM
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hey guys , i have twin turbo 5.0 stock botom end just rebuilt,trickflow heads and cam,systemax intake and 39# injectors with C&L MAF. the car has not been tuned as of yet, the problem is when i roll into the throttle and it starts to make boost around 2-3 psi the bypass valves will open and close and open and close and keep doing that until i let of the gas.i had this same issue last year with a totally stock motor and now im having it again and dont know what it can be.the weird thing is when im in 1st gear it will go and make 10psi and the car screws,every other gear it keeps opening and closing the valves...what can cause this? what should my timing be set at? do i need a timing retard at all? could it be the C&L? some guys say they are no good.
oh and im using external W/Gany help would be aprriciated. thanks- justin
first timing should be set at 10* with the spout disconnected. you dont have enough injector. what size turbos are you running? how much boost are you trying to make? what size springs in your wastegates? what brand wastegates? what kind of tune do you have now? if you are on a stock tune I wouldn't be running it. I dont think the stock timing curve and injector pulse is gonna be safe. what are you using to tune? sct? if you're using sct take it the chip to your tuner and have him lay down a safe tune to limp the car to him. I would not be getting into boost if I was you.

92 Chameleon Hatch.
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post #5 of 24 Old 06-06-2011, 10:54 PM Thread Starter
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My timing was set for 10*. Turbos are .63/.60 60mm. W/G are turbonetics each has 5psi spring in it. I do have an sct chip and it was tuned last year with this setup on a stock motor. I had this same problem last year with the bov's opening and closing when it started to make boost. When it was on the dyno last year it would rev to about 3500 then cut out. I could never figure it out last year so over the winter I built this motor all new and having the same issue. Should I jump up to 60# injectors? I have an appointment this week back at the dyno. I think I'll tow it there
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post #6 of 24 Old 06-19-2011, 06:37 PM
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Maybe you have a combination of problems. If you only have 5 psi springs in, are you sure it's not the wastegates opening? i'm assuming they are vented to atmosphere. What are your plugs gapped at?

Jeremy
1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
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post #7 of 24 Old 06-19-2011, 06:48 PM Thread Starter
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Plugs are gapped at .030 and yes wastegates are vented to atmosphere. How can it be the WG if it's only making 2-3 psi? Sometimes in 1st gear if I floor it
, it makes 10psi but very rarely.
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post #8 of 24 Old 06-19-2011, 06:58 PM
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Plugs are gapped at .030 and yes wastegates are vented to atmosphere. How can it be the WG if it's only making 2-3 psi? Sometimes in 1st gear if I floor it
, it makes 10psi but very rarely.
Where is your boost gauge referencing? I've seen big variances in boost if the wastegates are seeing boost from the compressor and your gauge is reading it from the manifold...

You might have a fuel or spark issue while under a load if it's boosting fine in 1st, but not in other gears. Just another thought. There are really a lot of variables and it's kind of hard to diagnose without having hands on.

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post #9 of 24 Old 06-19-2011, 07:01 PM Thread Starter
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I have it right into the vacuum tree on the firewall. I think the only thing on that is source and brake booster.
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post #10 of 24 Old 06-19-2011, 07:22 PM
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I didn't see if you had an ignition box or not. I would try setting the total timing to around 15* with the SPOUT out and leave it out (So 15* total), and then gap the plugs down to .026 and see if it makes any difference.


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1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
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post #11 of 24 Old 06-19-2011, 08:52 PM Thread Starter
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I can try that. Yes I have an msd 6al,distributor and coil.
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post #12 of 24 Old 06-19-2011, 08:58 PM
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I can try that. Yes I have an msd 6al,distributor and coil.
Ok, good.

Do you have a picture of your setup? Do you have the MAF in drawthru or blow thru config? I'm assuming you have the MAF in blowthru config located between the BOV's and throttle body.

If the spark and timing doesn't help, it's most likely a tune issue as maybe the fuel map isn't jiving with the MAF and injectors... just thinking out loud. What C&L do you have? A 76mm MAF? Does it have the proper cal tube in it? Just have to ask.

Sorry for all of the questions, but there are a lot of variables!

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1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
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post #13 of 24 Old 06-19-2011, 09:12 PM Thread Starter
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Yes it's a blow thru 76 C&L maf. It has a tube for 42# that's what the guy from C&L said I should run because the cobra 39# injectors are just about the same as the 42's. Could that small of a difference make this problem?
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post #14 of 24 Old 06-19-2011, 09:31 PM
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Yes it's a blow thru 76 C&L maf. It has a tube for 42# that's what the guy from C&L said I should run because the cobra 39# injectors are just about the same as the 42's. Could that small of a difference make this problem?
It's possible that it could make a difference. It almost sounds like it's too fat. What is your fuel pressure adjusted to with the vacuum off the regulator?

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1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
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post #15 of 24 Old 06-19-2011, 09:42 PM Thread Starter
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I forget what it's set with vacuum off. But it's set for 40# with vac on. Maybe I should get a set of 42# injectors just to see if that makes a difference. I had this problem last year on stock H/C/I and the tuner culdnt even figure it out on the dyno.
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post #16 of 24 Old 06-19-2011, 09:49 PM
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I forget what it's set with vacuum off. But it's set for 40# with vac on. Maybe I should get a set of 42# injectors just to see if that makes a difference. I had this problem last year on stock H/C/I and the tuner culdnt even figure it out on the dyno.
It could be the culprit (injectors), but it's hard to know without a wideband hooked up.

The fuel pressure could be high as well, but that's hard (and dangerous) to diagnose without the wideband.

I ran the 76mm C&L with 42's and about 43 lb of fuel pressure with the vacuum off at idle (and then replaced the vacuum line). I'm not sure what the pressure was at idle with the vacuum on. I just added more fuel pressure until my WOT AFR was correct. I had to make a vacuum leak for it to idle smooth because it was rich, and still have fuel at the top end to not run lean. That was a great driving car with no tune and timing locked at 26* with race gas. I went 9.81 @ 139 mph like that.

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post #17 of 24 Old 06-19-2011, 10:02 PM Thread Starter
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With my wideband with A/F is very lean at idle. When I drive it does get richer depending on how hard I accelerate. I may try the 42's I hate to buy them and still have the same problem.
How did you run your pcv? I have mine blocked off and running a breather in the valve cover. I can't even bring it to the dyno because he said he can't do anything until I fix this problem.
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post #18 of 24 Old 06-19-2011, 10:12 PM
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I'm a little surprised that your tuner can't take care of this for you. I brought in a basket case and both of the tuners that I've used have knocked it out easily. I have SCT chip on my current turbo'd '93 LX.

Jeremy
1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
1972 Maverick Sprint

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post #19 of 24 Old 06-19-2011, 10:21 PM
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With my wideband with A/F is very lean at idle. When I drive it does get richer depending on how hard I accelerate. I may try the 42's I hate to buy them and still have the same problem.
How did you run your pcv? I have mine blocked off and running a breather in the valve cover. I can't even bring it to the dyno because he said he can't do anything until I fix this problem.
I just used valve cover breathers as well on my '89lx. On my current '93 I have a hose that goes to the turbo inlet and it pulls crankcase air from the factory valve cover to an air/oil separator like for an air compressor hose.

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1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
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post #20 of 24 Old 06-20-2011, 01:30 AM
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Little confused on whats opening and closing, w/g or bov?
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post #21 of 24 Old 06-20-2011, 06:06 AM Thread Starter
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I thought it was the bovs,or it's some sort of vacuum leak or boost leak maybe???
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post #22 of 24 Old 06-20-2011, 08:28 AM
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Have you heard the wastegates open yet? With 5 psi springs and you said you've seen it climb to 10 psi in first gear... the wastegates should've been open, or aren't doing their job properly.

The BOV's should not be heard unless you take your foot out of the accelerator under boost or a sudden cause of engine decel causing vacuum in the manifold. Another issue could be that one or both Bosch BOV's are being pushed open by boost, but it doesn't seem likely at that boost level. I ran 22 psi on a Bosch type BOV.

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1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
1972 Maverick Sprint

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post #23 of 24 Old 06-20-2011, 08:53 AM Thread Starter
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I did hear the WG's working when it actually held the boost. They are brand new and I don't believe they are the problem. Everything seems to function properly but something is preventing the system from holding the boost,which I thought was my pcv system. I appriciate all the help your giving me
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post #24 of 24 Old 06-20-2011, 09:38 AM
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You can always buy a pressure check kit from someone like RacePartSolutions - Fast Parts At Discount Prices and pressurize your cold side from the outlet of the turbo to the throttle body and see if there's a leak somewhere. Honestly though, the only way I could see a boost leak affecting your cleanliness of a pull would be if the major leak was between your MAF and throttle body.

Do you have any pics of your engine bay? I'd like to see one so I can see your layout. Email to [email protected] if you do. Thanks!

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1992 Mustang GT, F150 Coyote swap, Mustang intake cams, 2018 Intake, JLT Cold Air, Fidanza V2 Clutch, G101a H-pattern, 2900lbs (work in progress)--10.60 @126 mph
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