I am working on my tune $59, and my MAP (kPa) data from my logs is:

$3f (used for fuel table) is 82 kPa and up, nearly 88 at idle and cruise (they are the same for all intents and purposes)

$3e (used for spark table) is 64 -67 kPa for idle and cruise as well

I have been questioning my hardware for a lot of reasons, this, and other inconsistant results like a tune being great, then the next time I start the car, NO CHANGE in the tune but it runs like crap, and other weird stuff. I pull fuel and get a nice AFR everywhere, then it suddenly goes rich
everywhere and I ahve to pull more fuel. I have done that three times now... I had it running really well and now its crapping out, only thing I have not checked is fuel pressure but it does not seem like the fuel pump would just get stronger idling in the garage.

I pulled my intake tube off and fired up the car, the turbo is moving a decent amount of air at idle and very low throttle but 88kPa at idle seems WAY HIGH. Looking at some older logs i see 75kPa at idle and cruise (so the numbers are the same), but that was in hotter air. I just cant beleive these numbers.

I am running a v8, 10.5:1 compression, mild cam, 85# seimen deka injectors. If anyone has a fuel map similar to this that doesn't mind me trying it I would appreciate it - or even a log with RPM and manifold pressure so I can compare

 

ok just did another log, the minimum kPa reading I get is 85kPA under hard decel in gear, that is NOT right. I think I found my problem, gonna investigate the MAP sensor and reference line tomorrow. Looking at past data logs the kPa readings have been averaging an upward trend - I think the sensor is going bad, anyone had this issue before? It seems to work fine in boost, as my tune has been great over 100kPA through all of this, AFRs are what they habve always been pretty much. Gonna have to pull the sensor and check the voltage output VS known pressures to see if its ok. Anyone have a chart of the volts/kPa that a GM 3bar Map should put out?

 

Here is a handful of data points for a 3-bar MAP. First column is voltage, second column is psi:

RBob.

 

My big cammed 400, 246/252 cam idles around mid 60's kpa when hot. I say you have some issues. On high rpm decel i have seen 20-30's kpa.

 

I run arround 45-50kpa at idle. Ive seen those 20-30's when deaceling also.

 

thanks for the numbers guys! I definitely have a problem based on them...

well I took a look at the MAP today - my epoxy repair on the broken reference tube barb failed due to heat. I also started the car and pulled a vacuum line, its pulling quite a lot of vacuum so I'm sure my MAP was the issue.

the epoxy I used to fix my old MAP became soft and lost its grip on the MAP case, I think it started coming apart on the HPD fun run I did (120 HOT, hard miles) when my car started running randomly and inconsistently. Looking back through my logs the absolute lowest MAP value, and idle value, has been creeping up each log - I think that was from the epoxy slowly letting go and causing a bigger and bigger vacuum leak.

 

put the repaired MAP on, ran better for about 5 minutes then got crappy again :/ watching my aldl data stream with the key on and applying vacuum and pressure to the MAP was not showing the correct trend, but there were no leaks so I assume I killed the MAP somehow...

put a brand new 3 bar map on $$$ and FIXED. I had to start over with the tune from scratch pretty much since I had gotten so far off track making it run with the crappy MAP. The up side to this whole deal is I got so much practice tuning a broken system that I got a tune nailed down so my afr's are within 6% or desired under 100kPa and within 3% up to 140-150 kPa in about two hours taking my time.

 

My 25 year old Map sensor failed without warning. No codes. Engine ran lean(on WB) and barely could maintain 50 MPH. Hard to diagnose. I should have datalogged but car got worse and I was fearfull I would end up getting a tow. Replaceing MAP sensor was a guess that worked.

 

glad to hear you fixed the problem .and thanks for the heads up on the symptoms of a bad map .

 

Yeah I'm lucky I didn't get stranded (almost did!). Its ridiculous how easy it is to tune now, I guess my MAP was not right since it was brand new.

This 3bar map was brand new off ebay (well 2k miles on it), bought a bwd brand one from o'reilly auto parts and is seems much better quality, case, connection, ect.

to add some more info to this thread, 3 bar MAP sensor part numbers:

GM: 12223861

BWD/o'reillys: EC1678/BWD

 

Ill add thats the same one I have. 3bar map. GM# 12223861

 

I just ran an msd 3 bar

 

One thing you can do is to warm up the engine then unplug the electrical connector on the MAP sensor. Data log and tune in the default MAP tables for when a MAP malfunction occurs.

This way if the MAP ever dies at least the car is still drive-able.

RBob.