Mechanics

CHEVY

2003 Chevrolet Express

Engine Performance problem
2003 Chevy Express V8 Two Wheel Drive Automatic 127000 miles

Hi
I have a 2003 Chevy Express 3500 with 6.0 motor that has 127,000 mi.

The motor idles rough and slow on hot start up.

It also hesitates, sputters and almost stalls when you try to accelerate in this condition.

If I rev the motor it seems to clear out excess gas and run fine.

The van starts, idles and accellerates fine when engine is cold.

The van showed a blinking p0102 code a few weeks ago and I replaced the MAF Sensor with an aftermarket Cardone model.

It didn't seem to help but the code didn't come back.

Since then all 8 fuel injectors and fuel filter have been replaced (oem injectors with aftermarket filter)

Fuel pressure regulator was replaced(GP Sorenson)

Idle air control valve was replaced(Standard Brand)

I have run 2 bottles of Techron through the system.

The P0102 code came back a couple of days ago so
I swapped the new MAF sensor for a new one because it has a 1 year warranty.

The van still runs the same.

I hate throwing parts at this problem but I am at a loss to find the problem.

I am thinking maybe a problem with the MAF sensor wiring harness. The plug looks o.K. And I added some dielectric grease to it for good measure.

Could a problem with purge solenoid or evaporative emissions system cause this.

More history about the van:
*Spark plugs replaced 110,000 mi with OEM irridium tipped plugs.
*Catalytic converters 82,000 mi.
* Bank 1 Sensor 1 O2 sensor 105,000 mi
*Plug wires 65,000 mi
* Air Filter 127,000 mi
*Bank 2 Sensor 1 O2 sensor 62,000 mi.
*Gas Cap 78,000 mi.
Thanksalot
Warren
Avatar
Precision
July 11, 2010.



Hi
Is this a Bi-Fuel? What is fuel pressure? Has engine compression been checked? As to the P0102 is low frequency fault will need hooked up to diagnostic scanner. If frequency is below 1200HTZ and does not increace with load and RPM then engine will have definate lack of power.
Let me know
Thanks for donate

Docfixit
Jul 13, 2010.
Hi,
No its not a BIFUEL motor.
I don't know what the fuel pressure is running at.
I don't have a pressure tester.
Compression has not been checked.
I only have a code reader no scanner so I can't check
frequency.
If I can get my hands on a scanner would I be checking frequency of MAF sensor?
Can you tell me if the MAF sensor harness goes right to the power train control module.
I have had some mice getting into the engine compartment occasionally I don't know if they may have damaged wiring.
Thanks
Warren

Tiny
Precision
Jul 16, 2010.
MAF terminal A yellow wire goes to PCM terminal 31 check continuity
MAF terminal B pink wire goes to ENG 1 fuse
Maf terminal C goes to ground
Check out and let me know

Docfixit
Jul 17, 2010.
Hi
I got a chance to do some diagnostics today.
Yellow at MAF plug to PCM 31 = 0.5 to 0.6 ohms

Pink at MAF plug to ENG 1 Fuse = 0.6 ohms

Black and White at MAF plug to good Ground = 0.5 to 0.6 ohms

Ignition on motor not running - I get 5 VDC to Yellow signal wire and tan wire at terminal D.
0.3 VDC to Tan wire at Terminal E

I also cleaned the PCM plug with electrical cleaning solvent.

I put it back together hoping it may have been a bad connection at PCM.
But it runs the same still idling rough after hot start.

Tiny
Precision
Jul 18, 2010.
Is there 12v+ on Term B pink wire key on? Have you tried cleaning MAF

Docfixit
Jul 19, 2010.
I'll have to check for 12v DC to Pink wire and get back to you.

A mechanic friend let me borrow a fuel pressure tester.

Here is the data: * Key ignition on motor not running spikes to 65 psi then drops to 60 psi and stays steady.

*Motor running smooth 56 psi

* Running rough the needle shakes quickly back and forth 55 to 57 psi.

Thanks
Warren

Tiny
Precision
Jul 19, 2010.
Check each injector resistence should be 11-14 OHMS

Docfixit
Jul 20, 2010.
Hi,
I checked the pink wire at MAF sensor plug.
It held steady at 12.55 VDC

I'm kinda doubting its the injectors.

Reason being is this problem exsisted before and after replacing all 8 fuel injectors with new Delphi injectors.
The injectors have about 5,000 miles on them.

I'd like to ask you the probability of my problem being related to some parts.

1. Power Train Control Module

2. Evaporitive Emissions Purge Solenoid or anything evaporitive emmissions related.

3. EGR Valve

4. Throttle Position Sensor

5. Absolute Manifold Pressure Sensor
This seems to feed info to the MAF sensor
Two tan wires terminals D and E.

If you could rate the above listed parts from not likely, Likely, and not likely at all it would be great

Also I am going to buy a scan tool that can read real time PCM module data, O2 Sensor data.

Any things I should check when I can read PCM and O2 sensor data?

.
Thanks alot
Warren

Tiny
Precision
Jul 20, 2010.
PCM No.1 all the rest not likely MAP semds manifold vacuum to PCM MAF sends air flow D & E are for Intake air temp. Really need diagnostic scan tool to help if you get one read missfire data also crank and cam sensor. Post results also MAF Htz

Docfixit
Jul 21, 2010.
Hello again,
It looks like I am going to have to buy a scan tool.
Could I buy any scan tool that displays real time PCM and sensor data?
I am thinking about buying this one because I don't have much money.
Unless you have any suggestions.

Thanks alot
Warren

Tiny
Precision
Jul 21, 2010.
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