Low Vacuum and Fine Idle - Dodge SRT Forum
 
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post #1 of 7 (permalink) Old 05-27-2011, 10:38 AM Thread Starter
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Low Vacuum and Fine Idle

This started a couple weeks ago. Right around the time I redid my catch can, breather, and had that last line on the brake booster pop off.

I've checked everything half a dozen times now, and everything appears to be connected properly and working. Trouble is, my vacuum still sits around 10 psi.

Idle is 800 RPM.
Stock gauge sits at 0 with engine off.
DSP confirms gauge's reading of 10 psi vacuum at idle.
If I pump the brakes while switching the AC on, brakes go stiff as it reaches 0 psi.
Emptied half a can of carb cleaner on all the vacuum lines I could find, plus IM and TB. Couldn't hear a difference.
Ran water all over the engine, hoses, etc while it was running, still couldn't hear a difference.
Been trying to do a boost test. First attempt got to 5 psi before I found a leak at the turbo side of the intercooler. Couple turns of the worm gear fixed that. Managed to test boost up to about 15 psi before I found a leak in my tester's threads themselves. Still got to fix that.
Recirc changes the AC fan sound when fan is on max.
On the street, if I push the boost hard it'll spike 20 psi no problem. (DSP tune)
Idle A/F is around 14.7ish.
If I pop the PCV line off at the TB, idle jumps and then settles down. Reconnecting the line then nearly chokes the engine until it settles again.

I'm at a loss with tracking this issue down. Messing with the PCV line and breather, neither is clogged or leaking. I don't believe my IM or TB has the leak either.
Boost test showed it holding 5 psi just fine and I couldn't hear any leaks this way. Does that mean the boost lines are probably good, but it's a CV protected vacuum line somewhere?
Once I get my boost tester fixed, I'll see about testing up to ~18 psi without any noise.
I've jiggled, shoved, and yanked every line I could find, and no change in engine sound.

At this point, I'm thinking I'll just have to start replacing vacuum lines with silicone until it's fixed. Is there anything else I could try? Could something be clogging a line or CV somewhere???

Thanks.


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post #2 of 7 (permalink) Old 05-27-2011, 04:08 PM Thread Starter
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And I think I figured it out. Frickin unit of measures. I didn't realize the boost gauge measures vacuum with inHg and boost with psi.

DSP shows 100 kPa BARO and 36 kPa MAP = -64 kPa = -9 psi = -19 inHg. So my engine is fine; Boost gauge is fucked. MPG is probably just off because I keep messing around trying to find a vacuum leak that isn't there.

For anyone else trying to figure out all these stupid unit of measures: Nice little pressure unit converter.


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post #3 of 7 (permalink) Old 10-01-2011, 01:47 AM
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Hey I was researching and cam to your page. I am having same issues with my Blue SRT but my engine is having a hard time staying alive. What I mean is it is though it wants to shut off but doesn't. Wish I can show the video of what I'm talking about. But everything is tight on the vaccum hoses. Just that hesitation sound blurp blurp blurp and -10 Vac. Rpm normal at idle. Backfire when heavy accelerating just test. Doesn't want to go pass 5100rpm on the street. I just change the Middle Mount from hell and ever since then it started. Did I f'd up something?
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post #4 of 7 (permalink) Old 10-02-2011, 10:13 AM Thread Starter
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My issue was just a bad gauge (still need to replace it). Everything else seems to be running fine. I even set a new MPG record the other week. Managed 28.2 miles to the gallon.

Backfiring is never good. Have you checked your plugs? Do you have a wideband or DSP?

I'm still an amateur at this, so have you checked your IAC? Pop the PCV line off your throttle body. Your idle should jump up, and then settle back down. That means, I think, that the IAC properly cut the air flow back due to the PCV leak. If the engine doesn't settle down after taking the PCV line off, IAC might be bad.

Still, with backfiring I would think it's something about either the plugs, too much fuel, or maybe timing.


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post #5 of 7 (permalink) Old 10-03-2011, 10:10 AM
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My plugs are 2 months old and with only 1000 miles on them. This all started when I changed the motor mount but prior to that I was having some IAC but it haven't caused me trouble lately since a changed my TB gasket. But my idle is normal. I think I f'd up my timing when i had to remove the Cam Idler pulley to remove the motor mount braket get to the Middle motor mount which I say is a pain to remove with little clearance. I Went back in there yesterday and thought I did not put the Tension back on the Timing belt correctly. Which I saw was incorrect to manufacture specs. So adjusted that, and also, tighten some screws in my Transmission that were vibrating loose from the engine. When I fired it back up problem still exist.
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post #6 of 7 (permalink) Old 10-03-2011, 10:15 AM
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I checked all my hoses and I have a new Boost gauge from MPx I don't have a wideband yet or DSP but, I am thinking it could be my MAP sensor or IAC solenoid. I test the MAP and its steadily at 4.9 volts. I believe is normal until you hook a Vacuum pump to it to test the volts during vacuum pressure increases volts should decrease per 5 pounds. Have not tried that but I don't think that's it. Why all of a sudden a MAP goes bad after changing the Motor Mount. Weird! So I dropped it off at the dealer. I no longer have time to look at it.
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post #7 of 7 (permalink) Old 12-04-2011, 02:03 PM
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It was my timing belt. the timing was way off.

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