Hi all,

Been only doing minor stuff on the ECM eprom side, in order to get the car "daily driveable" but not yet perfect (specially WOT). However, like most of us, time is short. Managed to find some useful time to tune again and start all over!

Doing that, I noticed that the MAP sensor readings seems to be real high when cold even at idle or very light throttle. It's in the range of 60-70-80... kpa at idle. All this when engine is cold. When hot, ok (25-35). But from time to time, a little spike here and there up to 50-60 for couple secs. Engine ok but sputters a bit when MAP sensor does that.

Was wondering, what are the readings you are getting from the MAP sensor when it's warming up? Is this normal? MAP sensor bad (>10 years old) ? Or just my imagination...? (I was planning on changing it, including the vaccum hose (vaccum hose seems ok but who knows, maybe a small leak...))

Any input on this is really appreciated. Thanks in advance.

BTW, since I couldn't get any kinda of ALDL cable working for my ECM (maybe laptop doesn't like them ) , I done a pretty basic one (2 wires and a laptop over LPT1) with my own software in DOS format. Nothing fancy, but it gets the job done (Flags, Formatted Output, Raw output, Error codes, saves BLM table, knock Table, spreadsheet compatible data log file). I've been playing with it for 2 years now, but I got to "better" it a bit more lately. I'll probably have something decent enough to offer to the list shortly. if anyone interested...

thanks,

 

Mark, what you are experiencing is contrary to logic. When the engine is cold, you tend to have a higher idle speed which usually gives a higher vacuum (and lower MAP reading).

If this is an original TBI engine, you may want to look for a Vacuum Leak which may be developing. Are you finding your idle speed "creeping" higher than normal? If so, the first place to scope out is the gasket between the TBI and the intake manifold. This is probably for the most common source of a vacuum leak for TBI engines.

As for a scan tool, do a search on "ALDL SCAN". There is a pretty slick scan tool for TBI cars/trucks in Windows mode and it's FREE!

 

Not original TBI engine (slightly modded), but the problem appeared slowly this winter. Idle hasn`t change... And That`s also what`s bugging me . Doesn`t make sense...
I tough about the vaccum leak: didn`t see anything at first check, but I`m going to do a 2nd check. (IAC numbers around 20-43, I`ll lower the idle screw a bit more to get around 20 IAC)

Now, if I understand correctly, such a behavior on the MAP readings during warm up isn`t normal. (Just making sure, I`m not looking for problems where there isn`t.... to me, there is )

Spring time is on over here and the car is due for the spring time tune up: Air filters, PVC, fuel filter, oil change... I`ll give a second look at the vaccum hoses, specially the one for the MAP making sure it is ok. If all fails, I was thinking about replacing the vac hose and then the MAP.

As for the WinALDL, It sure does look like a nice program! When it came out, I was eager to replace my "simple-but-yet-functionnal" personnal ALDL program. However, cable issues hasn`t permitted to get very far. Now, there is word over the GMECM list that an another transistor might help things. When I get time, I`ll look into that for sure.

Thanks for the input Glenn,