wishiknew

Hi guys, have a problem.
I have a suburban, 5.7 vortec. Ran good until I replaced the motor. (replaced due to low oil pressure - worn out everything at 220k miles) When I got it back, it had a serious starting problem. Whenever it was warm, it wouldn't stay running the first few seconds. It wanted to stall right out. No codes at the time, or for several months after. I got a MAF sensor code amongst many other things in the past two or three months that are most likely causing my added hesitation and increased fuel consumption, but where should I start with the stalling problem?

wishiknew

Come on guys, help me out here.

Darkman

There are many things that can cause those symptoms.

You do not report whether the replacement motor is new or rebuilt, but low compression is a possible cause. If there is any doubt about the intergrity of the replacement short block (e.g. it is used) I would start with a compression check.

Do you recall which MAF code you got?

Some of the other causes, other than low compression, include:

Fuel- inadequate fuel pressure from weak fuel pump, contaminated fuel or filter.
Ignition-worn plugs, plug wires, or distributor parts.
Air-vacuum leaks, unmeasured air getting past the MAF. Defective MAF.

RacerX

NMI-need more info.

What did u reuse from the old motor?

+ bad connection to the battery, leading to poor charging, faulty sensor.

jplinville

A dirty intake can do the same. Have you done a Seafoam treatment to it yet??

cleveland63b

From the wording I'm assuming you had someone install the engine for you? If thats the case I'd be giving them a call before digging into anything. Any worthwhile shop should have a warranty or atleast backup their work.

wishiknew

The intake was used off the original motor in the truck, and the rest was rebuilt. The block was bored .040 over, and pistons and rings to match. Block came out of a 74 camaro.
It was rebuilt by a friend of mine who was in school doing engine work.
MAF code was low input voltage. Can't remember the number off-hand.
The reason I don't think it's low compression is because the only symptom for a long time was the rough start. Everything else was happy. Accelerated well, had lots of power. Then I started getting codes for different things - knock sensor, O2 sensor, MAF sensor. Replaced the knock sensor, and the O2 sensor only comes on when the trans sensor does (the recall on the valve bodies for the 4l60e was never fixed in my truck so it hiccups once in a while) and again, never really noticed any driveability issues until the MAF sensor code came.
Battery connections are good - I check them every once in a while along with my fluid checks and changes.
Haven't done a seafoam treatment yet. Never really thought to.
Another idea I heard on these forums is the Fuel pressure regulator. How would I go about checking that?

RacerX

Did you replace the MAF sensor? There is a pintle in the MAF that can get clogged with dirt. Also there may be corrosion in the harness where the MAF sits in the air intake. And there may be a tear in the intake tube allowing more air in that should be allowed. Check the air intake tube for leaks, tears and poor fit. Duct tape what is ripped. Check for rust on the pins of the connector, jam some Vaseline in there to keep water out. And use a toothbrush to clean the needle off the MAF. Of course, knock-off Made in China MAF Sensors can give you the same symptoms.

This is an OBD II so it should give you precise explanation of the MAF sensor fault code, what does it say?

jplinville

Simple to do...suck a third to half of the can into the brake booster vacuum line, then shut it off. Wait about 5 minutes, then start it back up. Be prepared, though...it will puff so much smoke that they'll see it with the National Radar Service.

JimJ

Sugest that you take a pencil and paper and start writing these codes as they appear and when. Chances are that most of your problems stem from one or two things and by using a little logic instead of shotgunning you may be able to solve the trouble . Asking people to take WAGs and find the problem is like winning the lottery.