96 k1500 falls on its face(Fixed)

[bronc3buster842001]

My 96 is falling on its face at around 3k or so. Had a scan tool hook to it and my air fuel ratio drops to around 12 to 1 when it happens. Here is the data when it happens. Hope this makes sense to someone.


Engine speed 4388 rpm
TP sensor V 2.38 V
Engine coolant temp 190 degF
Intake air temp 2.94 V
Intake air temp 50 degF
Spark advance 28 deg
Iac motor poistion 200 cnt
Air/Fuel ratio 12.4 :1
Barometric pressure 29 iHg
Cam retard -1 deg
Engine coolant temp. 2.10 V
Engine load signal 71 %
FT Cell Bank 1 11 cnt
FT Cell Bank 2 11 cnt
KS activity 107 cnt
KS sensor 4.82 V
Knock retard 2 deg
Long term fuel FT Bank 1 9.4 %
MAP sensor 21 ihg
Short Term FT Bank 1 0.0 %
Short Term FT Bank 2 0.0 %
TP angle 50 %

 

[shady]

been there

the rubber hose in the gas tank that connects the fuel pump to to metal line coming out of the tank cracks. had to fix this on a 91 and a 95 chevy half ton. isnt that bad of a job to fix. get a couple of buddys over and unbolt the bed. you can easily move or remove it to get at the top of the tank. lot better than trying to drop it with gas in it. truck should run like a dream. couple of hours to check is better than throwing hundreds at it replacing stuff first, thats what we did, lot of preventative maintenance done though

 

[bronc3buster842001]

The fuel pressure checks out good. It runs fine till it hits 3k. Then you can ease out of it and it take off like it should.

 

[shady]

did on ours too but it must be a volume or air bubble thing. came up as getting lean on the air/fuel when we had it hooked up to the computer too. tried a lot of things on the 91 before we thought to check that. a buddy had found the same on a car he changed the pump on and brought it up. the 95 started acting the same a few months later and we checked there first. sure enough. there are 2 of those little hoses top n bottom of pump both bad on it.

 

[bronc3buster842001]

Bump.

 

[shady]

i take it its running good now

 

[bronc3buster842001]

No. Still runs like ****.

 

[shady]

oh thought bump meant like fist bump.

 

[496truck]

did on ours too but it must be a volume or air bubble thing. came up as getting lean on the air/fuel when we had it hooked up to the computer too. tried a lot of things on the 91 before we thought to check that. a buddy had found the same on a car he changed the pump on and brought it up. the 95 started acting the same a few months later and we checked there first. sure enough. there are 2 of those little hoses top n bottom of pump both bad on it.

12:1 is a rich condition. Just sayin.

 

[bronc3buster842001]

Ok. But what the hell is causing it to run rich at high rpm's.

 

[496truck]

Loss of ignition
injectors hanging open
dirty air filter
obstruction in the intake
bad MAP sensor
etc...

 

[Cornfield creations]

Maybe partially clogged converters? Can you run a back-pressure test? If you are running a 12.4:1 fuel ratio those converters are not going to last long

 

[bronc3buster842001]

What convertors. They was took off.

 

[Cornfield creations]

Ok then, that's eliminated. That is odd the A/F is off. That's controlled by the computer. Any codes or anything? Did you go into Global OBDII? Sometimes codes won't show up on the front door, but they do in the back door.

 

[bronc3buster842001]

Codes I get are for the tranny since I converted it to a manual. Also for the EGR valve which dont make any difference if its hooked up or not. I didnt find any hidden codes.

 

[496truck]

Is it a standard TBI injection or the Vortec with the central port (spider) injection?

Don't rule out the previously mentioned feed hose in the tank either. With enough pressure loss there will be uneven pressure delivered to the injectors which will cause missfiring and will show up as a rich condition via the O2 sensor.

 

[bronc3buster842001]

It is the vortec CPI.

 

[bigblock72]

What was the actual fuel pressure? spec is 56-62 psi.

The most common problem is the mass air flow sensor gets dirty and causes all kinds of havoc especially under heavy loads and higher engine speeds.

 

[bronc3buster842001]

What was the actual fuel pressure? spec is 56-62 psi.

The most common problem is the mass air flow sensor gets dirty and causes all kinds of havoc especially under heavy loads and higher engine speeds.

Fuel pressure was around 55. Ive changed the mass air sensor, TPS, Iac, has a new dizzy and cap. even changed the Ecm with the one for my other truck.

 

[bigblock72]

Any codes?

Any other symptoms engine noises etc?

I've seen bad crankshafts position sensors cause wierd issues at higher engine speeds but is unusual.

Is your data in the first post going down the road with a load or in the driveway in neutral?

Will your scan tool read oxygen sensor voltage?