5400 RPM limitation with '96/'00 Vortec trucks

[Ed Wright]

Here is something that may help guys with Vortec trucks, that don't want to have to change to an LS1 style box. George runs a 4.3L S10. He is one of my NHRA stock Eliminator customers, from down in Louisiana:
_________________________

If you don't have the distributer right in the right spot it will act like a rev limiter. http://www.youtube.com/watch?v=OsE9OSm2UdE This was when I was trying to figure the problem out. You can hear what sounds like a rev limiter around 5400rpm. http://www.youtube.com/watch?v=PBM4SjJzZOE Here is me shifting at 6000 rpm with no problem. You have to grind off the lockdown tab and make it adjustable. I made a degree plate for the top of the distributer cap in 1 degree amounts. I then retarded the distributer a little at a time untill the problem went away.
__________________
George Roussel Jr. 4262 1996 S10 p-q/sa

He has not checked the retard on a scan tool, so I don't have any numbers for that. He just retarded the distributor (which houses the cam position sensor) until it went away.

Hope this helps somebody. George said to go ahead and post this.

[Hog]

Thanks for the input Ed. I was under the impression that the 5800-5900 rpm issue on the "black box" PCM's was only a problem with the V8 engines.

When I was researching this, the V6's were able to attain higher rpms while the V8 engines were still limited to 5800-5900rpms.


My distributer on my L31 is adjustable, so I might have to try that.

When my truck reaches 5800-5900 rpms, the injectors shutdown, then refire shutdown then refire very quickly, just like a rev limiter. This is with my limits set higher than the stock 5600 fuel cut off engine speed (bad VSS).

I dunno.
Thanks for the info though Ed. That trucks sounds pretty wicked for a V6.

peace
Hog

[Ed Wright]

I have not had a cammed V8 truck in here since talking to George, so have not had a chance to test it. I don't remember the V8 having a lock preventing moving it. Many of them need moved a tooth to get the cam sensor in time when they get here. Amazing how many guys (and some shops) can't even screw one back together correctly. He says his V6 would only go 5400 before. I haven't looked at his videos. He does have a good runnig little truck.

[Hog]

Yeah, I'm pretty sure the GM spec for CMP/CKP sensor correlation is plus or minus 2º, and I'm pretty sure it can be quite a bit furthur out of spec before you'll get a SES light.
I'm sure a lot of guys simply stab the distributer just to get them running and dont check the CMP retard correlation with a scan tool.

peace
Hog

[AJxtcman]

A few years back I had a full size 4.3L man trans truck. Not sure if it was 2wd or 4wd. When damp it would misfire. It came to me from another shop. They had replaced all of the Secondary Ignition System including the Distributor. They had replace the crank sensor also. Knowing the Cam to Crank correlation offset should be no more than +2° or -2° on a V8 I looked at this one. Hmmmmmm It was 15°. I had the shop install the old Distributor and it was 15°. I checked the timing chain and it felt good. Hmmmmmm. Then I looked up the spec
The Spec for a V6 is -5° to +17°.

The reason that the offset is tighter on a V8 is so the spark doesn't cross track in the cap. That is what I am having an issue with and I want this truck to go away.
I don't remember what type of V6 Dist I had. One type has a clamp that is attached to the Dist and won't rotate and the other type has a part of the Dist that goes around an alignment tab.
I think I had the clamp type and I cut the clamp off and replaced it with a V8 clamp, but it was about 4 years ago.
I rotated the distributor to get the offset to 0°. The truck had no more misfires for 2 years. Then it came back. It had a bad aftermarket coil





I hope this helps.

[n0dih]

When I had a tuner back in 05 tune my 96 Burb 350 it would rev to 5900-6000 rpm and hit the rev limiter, never pushed it, being stock and the familiy truckster, didn't feel the need to abuse it

Of course I don't think I have seen a factory tach accurate yet, most are off by 100 rpm or so.

As for cmp variation on the Vortec 454, mine reads -7.8 degrees and is physically hitting the intake to do that. Wish I could get it closer, but can't till I pull the dizzy out... What is spec?

[Hog]

There is quite a history of this issue.

Rev limiter on L31 Vortec350

fuel cut off and rev problem

The highest rev limits from the Lt1 guys?

Plus there are 4-5 other guys that have done the marineintake retrofit that experience the same 5800-5900 rev limit.

I agree with you on the stock tachs being off. Mine was off by almost 200 rpm vs. the scan tool. It reads correctly now.

peace
Hog

[Hog]

BTW the GM spec for CMP retard is + or - 2º.

procedure
TEST PROCEDURE
The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:

1. With the ignition OFF, install a scan tool to the DLC.
2. Start the engine and bring to normal operating temperature. IMPORTANT: Cam Retard Offset reading will not be accurate below 1000 RPM.
3. Increase engine speed to 1000 RPM.
4. Monitor the Cam Retard Offset.
5. If the Cam Retard indicates a value of 0°+/-2°, the distributor is properly adjusted.
6. If the Cam Retard does not indicate 0°+/-2°, the distributor must be adjusted.

ADJUSTING PROCEDURE

1. With the engine OFF, slightly loosen the distributor hold down bolt. IMPORTANT: Cam Retard Offset reading will not be accurate below 1000 RPM.
2. Start the engine and raise engine speed to 1000 RPM.
3. Using a scan tool monitor Cam Retard Offset.
4. Rotate the distributor as follows:

4.1. To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
4.2. To compensate for a positive reading, rotate the distributor in the clockwise direction.

5. Repeat step 4 until 0°+/-2°, is obtained.
6. Turn the ignition OFF.
7. Tighten the distributor hold-down bolt to 3 Nm (25 lb. ft.).
8. Start the engine, raise engine speed to 1000 RPM and recheck Camshaft Retard Offset.

peace
Hog

[AJxtcman]

Originally Posted by Hog

BTW the GM spec for CMP retard is + or - 2º.

procedure
TEST PROCEDURE
The ignition timing cannot be adjusted. The distributor may need adjusting to prevent crossfire. To insure proper alignment of the distributor, perform the following:

1. With the ignition OFF, install a scan tool to the DLC.
2. Start the engine and bring to normal operating temperature. IMPORTANT: Cam Retard Offset reading will not be accurate below 1000 RPM.
3. Increase engine speed to 1000 RPM.
4. Monitor the Cam Retard Offset.
5. If the Cam Retard indicates a value of 0°+/-2°, the distributor is properly adjusted.
6. If the Cam Retard does not indicate 0°+/-2°, the distributor must be adjusted.

ADJUSTING PROCEDURE

1. With the engine OFF, slightly loosen the distributor hold down bolt. IMPORTANT: Cam Retard Offset reading will not be accurate below 1000 RPM.
2. Start the engine and raise engine speed to 1000 RPM.
3. Using a scan tool monitor Cam Retard Offset.
4. Rotate the distributor as follows:

4.1. To compensate for a negative reading, rotate the distributor in the counterclockwise direction.
4.2. To compensate for a positive reading, rotate the distributor in the clockwise direction.

5. Repeat step 4 until 0°+/-2°, is obtained.
6. Turn the ignition OFF.
7. Tighten the distributor hold-down bolt to 3 Nm (25 lb. ft.).
8. Start the engine, raise engine speed to 1000 RPM and recheck Camshaft Retard Offset.

peace
Hog

V6 Document ID: 186951

Perform the Camshaft Retard Offset test procedure as follows:

1. Install the scan tool.
2. Start the engine.
3. Important: The camshaft retard reading is not accurate below 1000 RPM.
   
4. Raise the engine speed to the first specified value.
5. Monitor the camshaft retard with the scan tool.

Is the camshaft retard reading within the second specified value?
-5 to -17° @ 1000 RPM

[Programmer]

So is the V6 spec -5Deg to -17 or -5 to +17 ?