So I finally got the car working right. Turns out I've got the same issue as someone else on the board with the flyback board installed and the need to have PWM at 70%
Anyways, I got a stable idle, everything seemed good. The trouble is, idle shows about 60kPa (I'm at sea level).
I figured I had a vaccum leak, so I've tried the tirck with carb cleaner, spraying down different ports while running, trying to find the leak. So far no luck.
So I took the car out for a drive. If I let off the gas and basicly let the engine do the braking, my kPa reading will drop to the low 20s. As soon as I put the clutch in and let it idle, this moves back up to the low 60s.
This engine is fairly modified from stock, including lower comp pistons, porting, 5 angle valve job, moderate cams, and a turbo. It's a 4AGE that I'm going to use on my track car.
From the above info, does the 60 kPa idle reading sound accurate? btw, I have an after market vaccum/boost guage which at idle usually shows a pressure drop of about 12 in/hg, which supports the 60kPa reading.
Odd Map reading at idle > Now with another question on P2
Forum rules
Forum rules
Read the manual to see if your question is answered there before posting. If you have questions about MS1/Extra or MS2/Extra or other non-B&G code configuration or tuning, please post them at http://www.msextra.com The full forum rules are here: Forum Rules, be sure to read them all regularly.
Forum rules
Read the manual to see if your question is answered there before posting. If you have questions about MS1/Extra or MS2/Extra or other non-B&G code configuration or tuning, please post them at http://www.msextra.com The full forum rules are here: Forum Rules, be sure to read them all regularly.
Odd Map reading at idle > Now with another question on P2
Last edited by PSmurf78 on Wed Mar 22, 2006 9:04 am, edited 1 time in total.
I had the same thing.
I had the same thing on my motorcycle, a BMW K-75. I polled other K-75 owners, and everyone came back saying that I should see more vacuum than the 65-70KPA that I saw.
I searched for vacuum leaks, tested with multiple gauges, verified the valve clearances were correct, removed the turbo system to eliminate exhaust back pressure as a cause. Finally I did a leakdown test which showed that I needed new piston rings.
So, I rebuilt the top end with new rings, decarboned the pistons, lapped in the valves (they weren't leaking at all), reassembled everything, fired up and tested the vacuum again. 65-70KPA.
My engine's is sucking as much as it wants to suck, and won't suck any more. I suspect yours is the same.
My plan now is to just have a lot of MAP bins between my idle value and 100KPA to give me more control over this area despite the small range of MAP values that I'll be in when off boost. I haven't tried it yet, so no promises that this is the way to go.
I searched for vacuum leaks, tested with multiple gauges, verified the valve clearances were correct, removed the turbo system to eliminate exhaust back pressure as a cause. Finally I did a leakdown test which showed that I needed new piston rings.
So, I rebuilt the top end with new rings, decarboned the pistons, lapped in the valves (they weren't leaking at all), reassembled everything, fired up and tested the vacuum again. 65-70KPA.
My engine's is sucking as much as it wants to suck, and won't suck any more. I suspect yours is the same.
My plan now is to just have a lot of MAP bins between my idle value and 100KPA to give me more control over this area despite the small range of MAP values that I'll be in when off boost. I haven't tried it yet, so no promises that this is the way to go.
That's what I was wondering. Everything is brand new on this engine. New rings, new pistons, new hone on the block, new valves, new seats, etc. It was built up by a shop that build professional race engines.
Everything I've checked has been spot on, no issues at except for this map reading. What really gets me though is when coasting, it'll show ~25 kPa, which makes me think that what I'm seeing at idle is just what it's going to be. If I had a leak big enough to jump from 25 to 60, you'd think it'd affect the engine braking kPa too...
Everything I've checked has been spot on, no issues at except for this map reading. What really gets me though is when coasting, it'll show ~25 kPa, which makes me think that what I'm seeing at idle is just what it's going to be. If I had a leak big enough to jump from 25 to 60, you'd think it'd affect the engine braking kPa too...
-
djandruczyk
- MegaSquirt Guru
- Posts: 25
- Joined: Fri May 07, 2004 5:55 pm
- Location: Buffalo, NY, U.S.A.
- Contact:
If you can adjust ignition timing, Try advancing it and the vacuum should rise (kpa should go down) unless it's over-advanced already. If it's over advanced the idle can become unstable, if it's too retarded EGT's can rise quite a bit due to the fuel/air mix continuing to burn in the exhaust manifold and the engine's throttle reponse becomes poor, and off idle response will feel very "flat".PSmurf78 wrote:That's what I was wondering. Everything is brand new on this engine. New rings, new pistons, new hone on the block, new valves, new seats, etc. It was built up by a shop that build professional race engines.
Everything I've checked has been spot on, no issues at except for this map reading. What really gets me though is when coasting, it'll show ~25 kPa, which makes me think that what I'm seeing at idle is just what it's going to be. If I had a leak big enough to jump from 25 to 60, you'd think it'd affect the engine braking kPa too...
-
djandruczyk
- MegaSquirt Guru
- Posts: 25
- Joined: Fri May 07, 2004 5:55 pm
- Location: Buffalo, NY, U.S.A.
- Contact:
If you have a fairly aggressive cam, idle map readings will also suffer as well due to cam overlap (which isn't a good combo with a turbo). Also a Low CR andd/or short stroke motor will also lower intake vacuum levels.PSmurf78 wrote:Interesting... I'll have to try that tonight. Right now it's idling at about 12-12.5 degrees of advancement. I'll try playing with it and see what happens to idle and map readings.
So it could be the combo I have in there.
The cams increased duration from 232 (stock) to 252. It also added almost 2 mm of lift over stock 7.2 vs 9.1
Compression was dropped from 9.3:1 to 8.5:1. It seemed to me like that would have affected it some, but I wasn't sure how much.
The cams increased duration from 232 (stock) to 252. It also added almost 2 mm of lift over stock 7.2 vs 9.1
Compression was dropped from 9.3:1 to 8.5:1. It seemed to me like that would have affected it some, but I wasn't sure how much.
Last edited by PSmurf78 on Thu Mar 16, 2006 5:00 pm, edited 1 time in total.
-
djandruczyk
- MegaSquirt Guru
- Posts: 25
- Joined: Fri May 07, 2004 5:55 pm
- Location: Buffalo, NY, U.S.A.
- Contact:
check the timing as well and see if it makes any differences. Changing engine params like that (CR, cam specs) will alter timing requirements (CR more so than cam).PSmurf78 wrote:So it could be the combo I have in there.
The cams increased duration for 232 (stock) to 252. It also added almost 2 mm of lift over stock 7.2 vs 9.1
Compression was dropped from 9.3:1 to 8.5:1. It seemed to me like that would have affected it some, but I wasn't sure how much.
Hi there
I have a stock cam, no mods to the CR (app 8-9:1) and experience idling at 70kPa (seelevel as well). The AFR is 8-9 (!!) at idle, changing the VE makes the MAP readings even higher. Engine has been rebuilt quite recently. There is a supercharging on it though?
I am not sure if I should worry about it, the AFR values seem odd to me... Car is not smoking though or smelling.....???
Arnold
I have a stock cam, no mods to the CR (app 8-9:1) and experience idling at 70kPa (seelevel as well). The AFR is 8-9 (!!) at idle, changing the VE makes the MAP readings even higher. Engine has been rebuilt quite recently. There is a supercharging on it though?
I am not sure if I should worry about it, the AFR values seem odd to me... Car is not smoking though or smelling.....???
Arnold