MSGHUFF

iTrader: (7)

What would cause the map reading to drop under WOT? bad map sensor?

situation:
I was running at the track and on my last pass it felt like my fuel just cut off in 4th@6000 rpm.. when I got back to the pit area I reviewed my data log. The wideband showed I spiked up to 17.1 then down to 16.1 for the rest of the run. My initial thought was I only had an 1/8th tank of fuel and maybe I starved the pump/caught an air pocket ect... But, I also noticed my MAP dipped down into the 70's and fluctuated at the same time but.. my my tps was 100% and it went lean on both banks at the same time. So I got to looking at the sensor and its rubbing on the firewall when the motor is under load. I epoxy'd it on before the install to fix the rocking..... Does this sound like a bad sensor?
BTW I'm running an SD tune&mods are in my sig

txhorns281

iTrader: (12)

It's very possible that the MAP sensor could have come loose, especially on a FAST intake, leading to a small intake leak, which would explain lean spikes and lower manifold pressure readings. Have you tried to reseal it? I'd inspect that area and go for some data runs to see if the issue is resolved. Also, try using RTV as a sealer, alot of epoxies are a too brittle to allow for slight flexes when contact is made. Let the RTV cure for a few hours before reinstalling as well (duh!), and just be careful with any wire harnesses or PCV lines when reinstalling, I know it gets tight back there!

MSGHUFF

iTrader: (7)

If the MAP came loose under WOT wouldnt it stay at 100kpa? I epoxy'd it on and feels secure on the back..

SSpdDmon

iTrader: (10)

True - leaks would show as higher MAP readings since lower MAPs indicate higher vacuums. It sounds to me like there might have been some kind of obstruction in the intake tract. What puzzles me is the fueling error reported given PE is based on TP% and RPM. What does the MAF performance look like during the run (hopefully you have that)?

MSGHUFF

iTrader: (7)

I did happen to log all my maf PID's (even though I'm in SD) and it didnt change at all steady 11,200-11,800

Faulty MAP? it went from 100-77-77-75-72-89-86-87 I havent noticed anything different in the logs on the way home or this morning but I havent done any 1-4 blasts down the road either just quick 1-3 runs

SSpdDmon

iTrader: (10)

I wonder if there was a voltage spike (or lack there of). If your voltage dropped significantly during that part of the run, would your TB close some given it's an ETC setup? Then, fuel pump flow would also be affected as its output is directly related to voltage as well. Any chance you have some connections stressing under extreme conditions (keeping in mind traction at the strip is different than on the street)?

brad8266

iTrader: (23)

SSspdDmon,
You have a link to the thread that has the quote in you sig? I wanna read that thread, I imagine its funny. How the hell thou8ght there were wooden pushrods?

SSpdDmon

iTrader: (10)

https://ls1tech.com/forums/generation-iii-internal-engine/580973-changing-cam-car.html

txhorns281

iTrader: (12)

Now that I think of it, you're correct about that... Not sure what makes a MAP sensor go bad, but you should throw a MAP performance code if that were the case. Could be an electrical glitch, vettes are certainly prone to that sort of issue.

MSGHUFF

iTrader: (7)

Alright I did some more logging and its doing it as soon as I start making a lot of torque, every single time so the manifold is coming off in a few minutes...you can clearly see where its hitting the firewall so I will get the dremel out tonight also... I think the contact with the firewall is skewing the readings.

brad8266

iTrader: (23)

MSGHUFF

iTrader: (7)

Update: New map sensor fixed it. The old one was banging on the firewall hard enough to cut the fiberglass... I ground off the tabs on the new one and cut a small piece off the area it was hitting...