'02 Silverado runs rough..

[shortbed]

5.3 4x4...Most noticable between 45-55mph at part throttle (approx. 1200-1400 rpm) in 4th gear.The engine shudders sometimes so bad it rattles the exhaust! If I run it hard it doesn't have a problem, plenty of power.
It acts like the torque converter lock up problem I had last summer(replaced converter and solenoid) but the RPMs do not fluctuate
like that with this problem.
Not affected by engine temperature,does it cold or hot.
No engine light and no codes stored. I used a friends Modis to check it out
on a road test.The Modis shows no misfires when it is shuddering and all other sensor data appears normal. The troubleshooting section said to test alternator for AC current leak and that tested fine.
I checked fuel pressure and volume and that was fine as well.
The fuel pump and filter are about 6 months old.
I pulled the injectors Saturday and the inlet sides were clean,just a little crud on the outlet side that didn't take long to clean up.
Put OEM wires and plugs in it today and it still does the same thing.
It doesn't miss at idle so I don't "think" it would be an intake leak...
If it were a coil breaking down the Modis should've picked up on that..

Sorry about the long first post, just trying to figure out what I'm missing
Maybe one day I'll get to finish my Nova project!

[j cAT]

Originally Posted by shortbed

5.3 4x4...Most noticable between 45-55mph at part throttle (approx. 1200-1400 rpm) in 4th gear.The engine shudders sometimes so bad it rattles the exhaust! If I run it hard it doesn't have a problem, plenty of power.
It acts like the torque converter lock up problem I had last summer(replaced converter and solenoid) but the RPMs do not fluctuate
like that with this problem.
Not affected by engine temperature,does it cold or hot.
No engine light and no codes stored. I used a friends Modis to check it out
on a road test.The Modis shows no misfires when it is shuddering and all other sensor data appears normal. The troubleshooting section said to test alternator for AC current leak and that tested fine.
I checked fuel pressure and volume and that was fine as well.
The fuel pump and filter are about 6 months old.
I pulled the injectors Saturday and the inlet sides were clean,just a little crud on the outlet side that didn't take long to clean up.
Put OEM wires and plugs in it today and it still does the same thing.
It doesn't miss at idle so I don't "think" it would be an intake leak...
If it were a coil breaking down the Modis should've picked up on that..

Sorry about the long first post, just trying to figure out what I'm missing
Maybe one day I'll get to finish my Nova project!

the posting requires specific info...what fuel pump manufacturer? what was the fuel pressure??? what type spark plugs used???

I would also measure the resistance of the spark plug wires, and check that the plugs are of the same color....the ones removed..

then if nothing is found check compression...
the crankposition sensor which is under the starter motor may have a poor connection and also itself be dirty where the sensor looks at the timing ring,,,,

[shortbed]

Fuel pump is made by Airtex (Advance Auto Parts) Fuel pressure was 56psi running
Wires and plugs were AC Delco from dealer. The old plugs were in good color and uniform.
Crank sensor was clean.
I decided to check the fuel pressure again and used a friends gauge.
52psi key on 44psi running. Guess I know what I'm doing this weekend!
That pump doesn't even have 12,000 miles on it.Going to get the next one from the dealer.

[j cAT]

Originally Posted by shortbed

Fuel pump is made by Airtex (Advance Auto Parts) Fuel pressure was 56psi running
Wires and plugs were AC Delco from dealer. The old plugs were in good color and uniform.
Crank sensor was clean.
I decided to check the fuel pressure again and used a friends gauge.
52psi key on 44psi running. Guess I know what I'm doing this weekend!
That pump doesn't even have 12,000 miles on it.Going to get the next one from the dealer.

the pump to get would be the dephi pump...these are available at non gm dealer stores you will save some money....

airtex is well known for pump failures after a few months...

replace the fuel filter if you believe the pump has disintergrated this may have fouled the filter,,,and to be safe replace the fuel relay as this bad pump could have damaged the fuel pump relay contacts..

after you replace the pump always get the pressure guage out and check pressures .....give us some feedback on how you made out good luck................

[shortbed]

Put the new pump and filter in tonight(pump and filter from dealer) Replaced relay as well...
Same problem.
Still no MIL or DTC set.
Will be able to check the fuel pressure in the morning when I get to work.
Once again I'm thinking transmission..solenoid not holding proper line pressure,
rather than clutches slipping as the fluid looks and smells good.
There is no sustantial increase in rpm on the tach when the truck is shuddering-bucking.
....ding...fries are done!

[j cAT]

Originally Posted by shortbed

Put the new pump and filter in tonight(pump and filter from dealer) Replaced relay as well...
Same problem.
Still no MIL or DTC set.
Will be able to check the fuel pressure in the morning when I get to work.
Once again I'm thinking transmission..solenoid not holding proper line pressure,
rather than clutches slipping as the fluid looks and smells good.
There is no sustantial increase in rpm on the tach when the truck is shuddering-bucking.
....ding...fries are done!

your vehicle requires 60psi...with a new pump the pressure better be 60psi...

if the pressures are the same 44-50 psi then I would get another guage and also test the cal. on the guages used....drop the pressure guage and the cal is n/g...

with the low pressures if correct that you had,,,, with a new pump you should have seen some difference...as most find these pressures are big trouble ...

dtc should show random misfires...if not then the diagnostic's are off..

[shortbed]

Fuel pressure was 46 on his gauge. I need to get another one to verify,our dealer
comes to the shop on Wed. mornings.
Not sure what you mean about diagnostics being off.
If there are no codes being produced or stored the scanner has nothing to show.
Scanner being used is a Modis Elite with the 9.2 update

[wafrederick]

Do this,spray carb cleaner near the intake gasket area and notice for a change.The 4.8s,5.3s and 6.0s are known for intake gasket problems and Yes,the intake gaskets are made out plastic.Another place to get Delphi pumps is your nearest Carquest parts store,Delphi makes their fuel pumps now.

[jdmccright]

Not exactly familiar with the 5.3, but if it is low pressure and not the fuel pump, then I'd check the fuel pressure regulator if there is one. Hope this helps!

(Yup, there is one.)

[j cAT]

Originally Posted by shortbed

Not sure what you mean about diagnostics being off.
If there are no codes being produced or stored the scanner has nothing to show.
Scanner being used is a Modis Elite with the 9.2 update

if YOU know the engine is miss firing the computer had better have this data stored...if not something is wrong....usually any miss fire will be recorded...misses that you don't even know...

[2000CAYukon]

Originally Posted by j cAT

your vehicle requires 60psi...with a new pump the pressure better be 60psi...

if the pressures are the same 44-50 psi then I would get another guage and also test the cal. on the guages used....drop the pressure guage and the cal is n/g...

with the low pressures if correct that you had,,,, with a new pump you should have seen some difference...as most find these pressures are big trouble ...

dtc should show random misfires...if not then the diagnostic's are off..

j cAT,
I have the 2000 Factory Manuals. In the Fuel System Diagnostics section, it list the specs for fuel pressure as:

55 - 62 PSI with Ignition On/Engine Off

When the engine is started, the pressure should drop 3 - 10 PSI (It does not list a range for engine running)

My Yukon has 50 PSI with the engine running and was 58 PSI with the engine off. In my case, I was just checking. The Yukon is running fine. According to the Factory Manuals, I am within spec (unless I am misreading the specs).

I know that the specs for the 5.7 L31 engine are different but I was just curious if the 5.3 really requires 60 PSI (with the engine running). The Spider Assembly of the L31 really requires 60 but the design of the 5.3 may not require 60 PSI (with engine running).

My gauge is accurate and I had it checked against another gauge at a shop.

The LT1 Engine (I believe you own one) fuel pressure specs are 37 - 41 PSI (engine running) and you and I both know the LT1 moves the 4000 lb Impala pretty well.

So is my factory manual wrong? Do I have an issue with my Yukon if it has 50 PSI running (seems to be fine)?

Thanks,
2000CAYukon

[j cAT]

Originally Posted by 2000CAYukon

j cAT,
I have the 2000 Factory Manuals. In the Fuel System Diagnostics section, it list the specs for fuel pressure as:

55 - 62 PSI with Ignition On/Engine Off

When the engine is started, the pressure should drop 3 - 10 PSI (It does not list a range for engine running)

My Yukon has 50 PSI with the engine running and was 58 PSI with the engine off. In my case, I was just checking. The Yukon is running fine. According to the Factory Manuals, I am within spec (unless I am misreading the specs).

I know that the specs for the 5.7 L31 engine are different but I was just curious if the 5.3 really requires 60 PSI (with the engine running). The Spider Assembly of the L31 really requires 60 but the design of the 5.3 may not require 60 PSI (with engine running).

My gauge is accurate and I had it checked against another gauge at a shop.

The LT1 Engine (I believe you own one) fuel pressure specs are 37 - 41 PSI (engine running) and you and I both know the LT1 moves the 4000 lb Impala pretty well.

So is my factory manual wrong? Do I have an issue with my Yukon if it has 50 PSI running (seems to be fine)?

Thanks,
2000CAYukon

the spec is 62psi to 53 psi with the engine running ,,,then with the engine off should hold the pressure..with in a few psi...this is normal...

with the new pump installed the pressure is most often 60psi....when the pump gets older the pressure falls ..at the 53psi area I would say start looking for a good deal on a new dephi fuel pump...this is with the 4.8L to 6.0 L silverado engines..

on the 1996 impala LT1 the fuel pressure is 47 psi...this has not changed since new and it runs very good ...I have not recently reveiwed the lowest psi that is acceptable but It's probably the same ///with in a few psi with the engine running...

I have read but not witnessed this pressure drop when running, BUT this is a good test to do , as you know when the engine is under a heavy load fuel demand increases, and the pressure should hold ...if it drops the filter/regulator /lines/strainer/pump////all could be the cause of this...

don't you agree..

the question of 50psi is OK I would say no...reading these forums this is when the engines start acting up....random miss fires etc...

[j cAT]

I have read the 1996 test proceedure on the fuel pressures...
41-47psi is the correct pressures...then the most import thing is the the pressures don't vary when the engine is running ,,,,must be steady,,,any fluctuation means problems...

running lean random miss fires and O2 sensor excessive switching...

on engine shut down the pressures should hold steady,,,if it drops more than a few psi it is n/g...

so this is the same as the silverado except the truck/tahoes use higher pressures...

[luistito]

Originally Posted by shortbed

5.3 4x4...Most noticable between 45-55mph at part throttle (approx. 1200-1400 rpm) in 4th gear.The engine shudders sometimes so bad it rattles the exhaust! If I run it hard it doesn't have a problem, plenty of power.
It acts like the torque converter lock up problem I had last summer(replaced converter and solenoid) but the RPMs do not fluctuate
like that with this problem.
Not affected by engine temperature,does it cold or hot.
No engine light and no codes stored. I used a friends Modis to check it out
on a road test.The Modis shows no misfires when it is shuddering and all other sensor data appears normal. The troubleshooting section said to test alternator for AC current leak and that tested fine.
I checked fuel pressure and volume and that was fine as well.
The fuel pump and filter are about 6 months old.
I pulled the injectors Saturday and the inlet sides were clean,just a little crud on the outlet side that didn't take long to clean up.
Put OEM wires and plugs in it today and it still does the same thing.
It doesn't miss at idle so I don't "think" it would be an intake leak...
If it were a coil breaking down the Modis should've picked up on that..

Sorry about the long first post, just trying to figure out what I'm missing
Maybe one day I'll get to finish my Nova project!

HAVE U CHECK THE TPS resistance?

[shortbed]

Originally Posted by shortbed

5.3 4x4...Most noticable between 45-55mph at part throttle (approx. 1200-1400 rpm) in 4th gear.The engine shudders sometimes so bad it rattles the exhaust! If I run it hard it doesn't have a problem, plenty of power.
It acts like the torque converter lock up problem I had last summer(replaced converter and solenoid) but the RPMs do not fluctuate
like that with this problem.
Not affected by engine temperature,does it cold or hot.
No engine light and no codes stored. I used a friends Modis to check it out
on a road test.The Modis shows no misfires when it is shuddering and all other sensor data appears normal. The troubleshooting section said to test alternator for AC current leak and that tested fine.
I checked fuel pressure and volume and that was fine as well.
The fuel pump and filter are about 6 months old.
I pulled the injectors Saturday and the inlet sides were clean,just a little crud on the outlet side that didn't take long to clean up.
Put OEM wires and plugs in it today and it still does the same thing.
It doesn't miss at idle so I don't "think" it would be an intake leak...
If it were a coil breaking down the Modis should've picked up on that..

Sorry about the long first post, just trying to figure out what I'm missing

Back again!
I put a transmission in it from the dealer a couple of days after my last post.It ran great until about 2 weeks ago...
Now it's starting over again.Just like before it is getting progressively
worse.
Only seems to do it between 45 and 60 MPH in 4th gear with TCC engaged.
I didn't expect a GM "certified" transmission to have problems with only 2500 miles.
Transmission is under warranty but I have to R/R again!