map readings going high at idle

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kaeman
Master MS/Extra'er
Posts: 643
Joined: Sun Nov 06, 2005 12:31 am
Location: NORTHERN CALIFORNIA

map readings going high at idle

Post by kaeman »

I have encountered a problem, I am getting random vacuum levels, I have a mechanical gauge and 2 map sensors that show the problem, with the engine idling stable for a few minutes, all the sudden the rpm drops from 1100 to 700 and the afr's go rich , and the map readings rize from 55-60 to low 80's. the engine can be reved up and clear this out but it may come back in 1 minute or 30 seconds or maybe 10 minutes later. I am searching for possible vacuum leaks. but its a change that takes place in about 2 seconds and then will go away with out making any corrections..
in the attached log the problem occurs in the beginning a couple of times, I pump the throttle a few times and let the engine settle out, the engine idled normal at the end of this log for about 3 minutes at 1100 rpm and then the problem repeated itself. I shortened the log to fit so the size limit so that portion is missing.
2016-04-08_13.22.14.msq
2016-04-08_11_modified_modified.msl
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
nathanhardy
Master MS/Extra'er
Posts: 706
Joined: Sat Mar 17, 2012 10:13 pm

Re: map readings going high at idle

Post by nathanhardy »

I had my mapdaddy go out and it pretty much did the same bing if I remember right.. Don't want to lead you astray tho
98 VW golf gti vr6 turbo 8:5:1 cr ported and polished full ferrea race valves train 276 cams custom short runner intake Borge 366 sx-e turbo forge wossner pistons, balanced rotating mass, limited slip 6 speed deka 750Lbs injectors on ms3pro completed AWD swap
kaeman
Master MS/Extra'er
Posts: 643
Joined: Sun Nov 06, 2005 12:31 am
Location: NORTHERN CALIFORNIA

Re: map readings going high at idle

Post by kaeman »

I was headed towards possible bad sensor, but both sensors are showing the same readings and the mechanical vacuum gauge is showing the same drop. I called accufab yesterday and they said it might be my iac valve, they said they were sending me a new one this Monday, as they got a batch of them with a defect that caused vacuum leaks and mine might be one of the bad ones.
I am still looking into bad grounds and mechanical vacuum leaks. I haven't found the cause yet.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
kaeman
Master MS/Extra'er
Posts: 643
Joined: Sun Nov 06, 2005 12:31 am
Location: NORTHERN CALIFORNIA

Re: map readings going high at idle

Post by kaeman »

I changed out the iac motor and the problem seems to have cleared up. The last few times I have datalogged the engine the map sensors and vacuum gauge don't show the problem. The iac motor must have been leaking intermittently.
64 el camino, 383 SBC, 11.7 to1 CR, accufab tb/rhs intake, 44lb injectors, trick flow heads, xr292r solid roller cam, belt drive camshaft, dry sump oil system, 2400 stall, turbo 350, spooled 9 inch, strange axles, 3.89 gears, dual wideband, full sequential fuel/cop, MS3x using 1.4.1 code.
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