Vortec Intake Manifold Leak Symptoms

[mdiacont322]

Does anyone here know of the symptoms of an intake manifold gasket leak? The hoe is having the same issues its been having with the tuned pcm, but with the stock computer now. I unplugged the MAF, the problems went away. So i replaced the MAF, same problems. Im pointing to a vaccuum leak because of these stupid intake gaskets.

Any ideas?

Mike

 

[blueflamed03]

check front and rear, leaks were notorious on those.

 

[mdiacont322]

im getting the gaskets changed, the drivers side was pissing antifreeze. Would a bad gasket cause a p0300 to be hidden in the computer? the mechanic said that it was in the pcm but it didnt illuminate the SES light. The symptoms were sputtering, hesitation, and eventually popping out of OD between 70 and 80 mph, the mechanic specifically said about 2260 rpms. He said unplug the MAF sensor the next time it happens and see if it goes away. Sure enough it did. so i replaced the MAF and plugged it back in, same problems.

While changing the gaskets, the mechanic said the rotor was shot also, but I dont know how the MAF being unplugged would get rid of any symptoms that have to do with the rotor or intake gasket leak. The truck actually ran like a ***** f*cking ape with the sensor unplugged lol.

Mike

 

[andrew383]

Brake cleaner works real good for finding manifold leaks

If its running better with the maf unplugged you prob need to talk to your tuner..

 

[Jaycenk]

Yea but he said it did it on a stock tune as well. will it do it while in open loop? or is it just when it hits closed loop.

 

[mdiacont322]

what do you mean open loop and closed loop?

 

[Jaycenk]

PCM runs in two modes. well 3 actually but the first only last a min or something like that. Open loop is used by the pcm to allow the engine run cold untill the O2's and engine water temp come up to temp. It will not use the O2's to determine spark and fuel tables. It uses a only certian sensors to help it untill the O2's are up to temp and can be read by the pcm. If you have an intake leak of unmetered air getting into the engine the pcm will see it in the O2's sensors in closed loop and correct as much as it can. Thats why I ask if it will do it all the time or just when it's up to temp. In open loop it uses the MAF, MAP, TPS, IAT and Coolant temp sensors to help make it run. When you unplug the MAF i belive it throws the PCM back into open loop. If you know some one that has a data logging or live data scaner it may help pin point it by watching the fule trims to see if it starts riching up the trim in order to compinsate for the unmetered air. Or just swap the gaskets and see? Other things are coil ICM O2's and yes rotor and cap can cause a miss and hesitation. How old are the O2's?

 

[mdiacont322]

one o2 is brand new, i replaced it because the mechanic said it was lazy, all the other ones are in working order according to his scanner. My problems only occur when the truck is warm because I always let the truck warm up before i get on the highway. Ive never gone 70mph on a cold motor or trans.

So if the MAF sensor is unplugged, it throws the computer into open loop mode? That is when the symptoms disappear. If its plugged in, I have the symptoms.

It is actually only at a certain cruising rpm in overdrive, once it hesitates or misses for long enough, it kicks it out of OD, leaving it in 3rd gear.

Mike

 

[Jaycenk]

Well if you have a vac gauge that may help, I would assume the mechanic would have already checked that though. So it only will do this when your in over drive at around 70mph?
You need to data log it at that rpm and speed to be able to see if it is an actual misfire being read by the pcm. If it's reacting to the misfires by unlocking the converter and down shifting it's enough for the PCM to trigger an event. For instance I have an Innova scaner that is cabible of data loging a couple of ways. I can tell it to only log when a DTC (diagnostic trouble code) is trigered by the pcm to start loging or I can manually tell it to log. When I log by DTC event it will take a freeze frame the instant the DTC is triggered. Helps you see what the pcm saw at that very instant. It's kind of od to be only happening at that speed though. You have no problems at slower speeds?