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Old 01-19-2005, 09:48 PM   #1 (permalink)
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input needed, low vacuum

well like it says i have a low vacuum problem. its causing a code 45 to rich too lean fuel trim malfunction. my guess is because the low vacuum is causing the fpr to allow more fuel. but anyways thats not the point.

now i do have crower stage 2 cams with modified idle lobes but i just cant see how they could reduce the vacuum this much. at warm idle its around 440-450mmhg, not insanely low but 17 inches is on the low side since it should be in the low 20's. the map sensor voltage is around 1.28-1.31 and should be below 1v at warm idle.

and yes, before anyone asks

compression 1-4 255,255,255,265 (type s pistons)

leakdown = slightly over 6% across (not to shabby)
**edit** this would rule out valve adjustment also.

all vacuum lines checked with throttle body cleaner = negatory.

one thing i did do like a dumbass back when my car was all jacked up was cut the tip off the idle adjustment screw so i could keep the pig running. im just wondering if that cut off tip is allowing enough of a vacuum leak to cause this. mechanically everything seems to be sound except my bad valve seal on cylinder 4 but that isnt an issue.

anyone with crower 2's with moded idle lobes, could you chime in with your idle vacuum readings? i know my vacuum is going to be lower but not this low. im getting ready to switch over to uberdata but i want the vacuum problem solved before i start to tune it. if i dont its going to mess up where i sit on the fuel and timing maps at idle.

thanks
rick
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Old 01-19-2005, 10:17 PM   #2 (permalink)
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I have the same cams you have. I checked the manifold vacuum when I first fired the car up, and about 17inHg sounds pretty close to what I measured. I haven't had any fail codes though. For reference, my car is an '01 SS. I have an Apexi VAFC, and everything else is original. I do have 8% fuel removed at idle, so maybe that puts me in a safe region since the VAFC modifies the MAP signal.
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Old 01-20-2005, 12:16 PM   #3 (permalink)
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What is your idle speed? Vacuum should not possibly be a problem if your idle speed is correct.

I would not rule out the valve adjustment. You've ruled out the adjustment at TDC with a leakdown but I would still make sure it is in Honda spec.

The ECU will correct for closed-throttle VAFC corrections within seconds. I wouldn't think that's doing anything or a possible solution.
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Old 01-20-2005, 03:55 PM   #4 (permalink)
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Quote:
Originally Posted by marcucci
What is your idle speed? Vacuum should not possibly be a problem if your idle speed is correct.

I would not rule out the valve adjustment. You've ruled out the adjustment at TDC with a leakdown but I would still make sure it is in Honda spec.

The ECU will correct for closed-throttle VAFC corrections within seconds. I wouldn't think that's doing anything or a possible solution.
idle speed is between 700 and 800, it mostly sits around the mid 7's like it should.

the valve adjustment is supposed to be done at tdc of each cylinder. if the leakdown numbers are showing good things then how could it be the adjustment. if it were to tight, even at tdc the leakdown numbers would be bad. regardless im still going to check it this weekend.


leaning the vafc out in low throttle did actually help. the problem is its running rich beyond the ecu's capabilities of trimming it ,thus the code 45. by leaning it out i can bring the ecu back into the territory where it can control the closed loop fueling correctly again.

i tried trimming only at idle but the stft data the ecu saw (at idle) and the stft data it saw everywhere else (above idle to redline) where it wasnt leaned must have been a conflict and the ltft kept swinging back and forth. this was causing drivability problems so i decided to lean the low throttle out at the same number the entire way from idle to redline. sorta an attempt at fooling the ecu all of the time as opposed to some of the time. well it seems to be working. i have driven a total of about 2 hours like this now and it still doesnt buck or hesitate like it did when i only had it leaned at only idle. also the wideband is showing normal closed loop operation everywhere else so the ecu is still able to do its job with the rest of the rpm.

its actually quite nice having the low throttle leaned out like this. a reprocussion is its messing with the ltft and i do not need to pull as much fuel out in the high throttle map because the ltft is allready doing it for me. and whats even nicer is that that doesnt have an effect of timing like the vafc does.

i guess all of this is in vain though since i should have uber up and running in a week or two. just having a hard time locating an automatic p28 close by.
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Old 01-20-2005, 03:57 PM   #5 (permalink)
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btw anyone else with these cams crower stage 2's with mod idle lobes please chime in with your vacuum numbers (preferably warm idle) if you would be so kind. i may be chasing ghosts and this vacuum maybe normal.
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Old 01-20-2005, 07:42 PM   #6 (permalink)
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Ok, I got the same setup as you, the cams, the pistons ect. I run an adj. fpr and I also cut my throttle screw. So we are similar, I also threw the same code 200 miles into breakin. Through my finding I had no vacuum leak, but I did find that if I backed the fuel pressure off about 3 pounds at idle I had no problems. For whatever reason I wanted a little less fuel pressure. Id check that (fp). Do you run a stock fpr? The cams shouldnt affect vacuum, I wouldnt think the idle would either, being so close to stock. My car didnt hardly want to idle at all and it worked fine after the pressure adjustment
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Old 01-21-2005, 07:55 AM   #7 (permalink)
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Quote:
idle speed is between 700 and 800, it mostly sits around the mid 7's like it should.
I would bump the idle speed and see if it helps. Does the CEL come on at idle, without driving anywhere?

Quote:
the valve adjustment is supposed to be done at tdc of each cylinder. if the leakdown numbers are showing good things then how could it be the adjustment. if it were to tight, even at tdc the leakdown numbers would be bad.
I'm not saying the valves are too tight. I'm saying you can still get a CEL for valves because they are too loose or too tight, even if they shut all the way at TDC. This wouldn't indicate a vacuum problem, just a fuel one (to the ECU).

Quote:
leaning the vafc out in low throttle did actually help.
I am shocked. On Preludes and Civics I have tuned, a 5-10% change is trimmed out (at idle) within about 5 seconds. I have verified this with a wideband. All I can think is that maybe if the cams or whatever throw the stock maps way off, by altering the MAP signal more towards where it should be it makes the ECU "happier" by reducing the amount of trim it THINKS it's applying. Regardless, the ECU will always try to wrangle the AFR back to stoich when closed-loop.

Quote:
the problem is its running rich beyond the ecu's capabilities of trimming it ,thus the code 45. by leaning it out i can bring the ecu back into the territory where it can control the closed loop fueling correctly again.

i tried trimming only at idle but the stft data the ecu saw (at idle) and the stft data it saw everywhere else (above idle to redline) where it wasnt leaned must have been a conflict and the ltft kept swinging back and forth. this was causing drivability problems so i decided to lean the low throttle out at the same number the entire way from idle to redline. sorta an attempt at fooling the ecu all of the time as opposed to some of the time. well it seems to be working. i have driven a total of about 2 hours like this now and it still doesnt buck or hesitate like it did when i only had it leaned at only idle. also the wideband is showing normal closed loop operation everywhere else so the ecu is still able to do its job with the rest of the rpm.
So it is fine now?
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Old 01-21-2005, 11:50 AM   #8 (permalink)
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Quote:
Originally Posted by marcucci
I would bump the idle speed and see if it helps. Does the CEL come on at idle, without driving anywhere?



I'm not saying the valves are too tight. I'm saying you can still get a CEL for valves because they are too loose or too tight, even if they shut all the way at TDC. This wouldn't indicate a vacuum problem, just a fuel one (to the ECU).



I am shocked. On Preludes and Civics I have tuned, a 5-10% change is trimmed out (at idle) within about 5 seconds. I have verified this with a wideband. All I can think is that maybe if the cams or whatever throw the stock maps way off, by altering the MAP signal more towards where it should be it makes the ECU "happier" by reducing the amount of trim it THINKS it's applying. Regardless, the ECU will always try to wrangle the AFR back to stoich when closed-loop.



So it is fine now?

i have actually verified the same thing you have with a wideband. and under any normal circumstance it would hold true. but, in my case my fuel trim was so thrown off that the ecu no longer had the ability to lean it out anymore to get rid of the rich condition. i looked at a near stock h22 .BIN in uberdata and cross referenced the vacuum/rpm i am seeing on my vafc to its appropriate cell on the map and i can see what the problem is now. at that vacuum there is just no way the ecu can trim enough fuel, well at least within its +/- 20% limitations. the cells the ecu would normally see at idle from 20-24 inhg and 500-1000ish rpm range from 34 - 45ish on the fuel table. the cells its actually idling in with the 15-16 inhg of vacuum are ranging anywhere from 111 - 175. these cells are actually meant to be used under some sort of load and since the engine isnt under any load at idle its just way to much fuel. couple that with the fuel pressure regulator rising the pressure from the lower vacuum and its just captain insane-o rich. 10 out of 10 times it stalled the wideband would show AFR's in the high 10's low 11's

the whole goal with the vafc was to lean it enough to bring the ecu back into its +/- 20% range so it could again start looking for stoich. one of the GOOD by-products of that was that the ltft settled more in my favor. i have known that low throttle adjustments would carry over into the ltft. but in this case it helps me because at 7000rpm i no longer have to have the vafc leaned out 12%, now its leaned about 6%, which helps combat the timing problem caused by the vafc.

all in all it's not the best fix but it works till i can get my p28 an get uber going and actually alter the cells it idles in. the cell did turn off too.but, the idle still does suffer a little but its now a timing problem from leaning it out with the vafc rather then a fueling issue.

so i guess the problem is partially fixed. i still do believe something mechanical is lowering the vacuum beyond what it should be. stock vacuum is above 20inhg so a drop of 4+ inhg just seems a bit much for these cams. sure the idle lobes are modified but these arent toda D's or buddy club spec 3's. i doubt highly its a vacuum leak because my idle doesnt hunt (except in the morning from the coolant bypass an fitv block) and my pressure readings are pretty constant. i am going to retorque the intake manifold bolts though. that hondata gasket doesnt leave much for the nut to grab onto. i may replace the injector o rings too since they are cheap and i want pull the injectors anyway to get them cleaned.

oh i checked the EGR also and it appears to be working properly. who knows with those things though. from what i see they are a real problem for preludes and accords. when i switch to the p28 im going to block it off.


btw sorry for the long posts. i like to type out loud and be as descriptive as possible.
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