'98 5.7 Misfiring

[98Z]

Last week the wife took my truck and when she returned, she said that they SES light had come on but had gone out not too long after. She said that the truck seemed to run fine but wanted me to know about the light. Yesterday, I took off (truck had sat one full day at least) and there was a bit of a stutter in the acceleration and it seemed to vibrate at low speeds. If I'd give it more throttle or accelerate harder, it didn't do it. I took it to the next town over (15 miles) and by the time I'd gotten there, the SES light was on again (not sure when it had come on). When I returned to town, I stopped in at a shop where I know a couple of the guys. I was lucky enough to get one of them to scan the computer (and clear the codes so the light would go off). I don't know if he actually told me the code number(s) that it gave, but he did tell me that it showed some misfires. He told me that the computer had recorded misfires on all 8 cylinder. He suggested that I check/replace the distrib. cap and check the plugs. The rest of the day and all day today the truck has acted just fine. There have been other times when I have experienced the hesitation and vibration but never had the light come on until recently.

Anyone else concur with this or have other ideas?

[maxwedge]

Originally Posted by 98Z

Last week the wife took my truck and when she returned, she said that they SES light had come on but had gone out not too long after. She said that the truck seemed to run fine but wanted me to know about the light. Yesterday, I took off (truck had sat one full day at least) and there was a bit of a stutter in the acceleration and it seemed to vibrate at low speeds. If I'd give it more throttle or accelerate harder, it didn't do it. I took it to the next town over (15 miles) and by the time I'd gotten there, the SES light was on again (not sure when it had come on). When I returned to town, I stopped in at a shop where I know a couple of the guys. I was lucky enough to get one of them to scan the computer (and clear the codes so the light would go off). I don't know if he actually told me the code number(s) that it gave, but he did tell me that it showed some misfires. He told me that the computer had recorded misfires on all 8 cylinder. He suggested that I check/replace the distrib. cap and check the plugs. The rest of the day and all day today the truck has acted just fine. There have been other times when I have experienced the hesitation and vibration but never had the light come on until recently.

Anyone else concur with this or have other ideas?

Trust your mechanics here that is the basic starting point for that condition, how old, miles, are the plugs and wires?

[98Z]

Maxwedge, I can't really answer that. I bought this truck a few months ago and haven't done much of anything to it. The plugs and wires both look fairly new. The wires are still clean and the metal on the plugs is clean and rust free. I can't imagine they are very old. The truck has 156K on it.

[wafrederick]

It might be a worn out distribitor gear.The distribitor gear is a common problem,most dealers and auto parts stores stock them.It will cause a miss and I have seen that happen.Had one miss and put new set of sparkplugs that did not cure it.Finally pulled the distribitor out and the distribitor gear was worn out,had shiney spots.Installed a new distribitor gear, put the distribitor back in and ran fine after setting the distribitor with a scan tool.

[chevrock22]

has the timing been checked?

[MT-2500]

Originally Posted by chevrock22

has the timing been checked?

The timing is not adjustable on them.
But if the cam retard setting is way off it may cause engine running problems.

PS
Chevrock22
If you are so proud of that and want to use my quote make sure you put quoted from by MT-2500
I have copy rights on part of it but I will loan it to you as long as you state quoted from MT-2500
Or better yet post the hole thing and give Kenney rodgers the credit on his part.
MT

[bracketshark]

I had this problem on a 97 model not long ago, I replaced plugs, wires, cap and rotor. Nothing made much differance, my problem was cured by adding Chevron with Techtron fuel additive (its in a black bottle) through a couple of tanks of gas. It seems the injectors plug somewhat if not cleaned after a period of time. If you've ever changed the intake gasket on one you can see how crappy the outside of the injectors get. I would think in your case with that many miles it has already been changed if not it will soon. By the way the timing sets with the distributor just as the older units only it can't be set with a light, it must be done with a scan tool that only the dealers have (in my area) the timing sets at + or - 2 deg. from 0, the computer will handle it from there, it will run up to 16 deg. out of timing but the check engine light will burn, + or - 2 deg. from 0 will not turn on the light. Good luck with your repair it probably won't be very much fun.

[98Z]

After my mechanic friend reset the computer and I've run a full tank of gas through it after adding AC Delco Fuel Injector Cleaner ($10.00) to it, I have not yet experienced any of the aforementioned hesitation or sputtering and I haven't seen the SES light. For now I guess I'll just keep an eye on things and wait to see what happens. Thanks to all for the suggestions.


Dave

[MT-2500]

Originally Posted by bracketshark

I had this problem on a 97 model not long ago, I replaced plugs, wires, cap and rotor. Nothing made much differance, my problem was cured by adding Chevron with Techtron fuel additive (its in a black bottle) through a couple of tanks of gas. It seems the injectors plug somewhat if not cleaned after a period of time. If you've ever changed the intake gasket on one you can see how crappy the outside of the injectors get. I would think in your case with that many miles it has already been changed if not it will soon. By the way the timing sets with the distributor just as the older units only it can't be set with a light, it must be done with a scan tool that only the dealers have (in my area) the timing sets at + or - 2 deg. from 0, the computer will handle it from there, it will run up to 16 deg. out of timing but the check engine light will burn, + or - 2 deg. from 0 will not turn on the light. Good luck with your repair it probably won't be very much fun.

The timing is not adjustable.
You can turn the dist all day and it will not change the timing.
It only changes the cam retart which is a not a timing adjustment.
MT

[chevrock22]

Originally Posted by MT-2500

The timing is not adjustable on them.
But if the cam retard setting is way off it may cause engine running problems.

PS
Chevrock22
If you are so proud of that and want to use my quote make sure you put quoted from by MT-2500
I have copy rights on part of it but I will loan it to you as long as you state quoted from MT-2500
Or better yet post the hole thing and give Kenney rodgers the credit on his part.
MT

Im not giving you credit this is there as a joke. And yes the timing can be set on the cams.

[MT-2500]

Originally Posted by chevrock22

Im not giving you credit this is there as a joke. And yes the timing can be set on the cams.

THE IGN TIMING IS SET BY THE CRANKSHAFT SENSOR AND ADVANCED WITH PCM/VCM.
The cams and the dist has no part in it.
If you are going to use a quote from any of my post please quote the hole thing and state that is is my quote.
Otherwise it is copyright stealing.
MT

[MT-2500]

Originally Posted by chevrock22

Im not giving you credit this is there as a joke. And yes the timing can be set on the cams.
Quote from chevrock22 signature= "It is time for you to fold and move on will you are ahead.
If not the moderator may be along to read you you your rights."
-MT-2500-

As you can see here them words were stolen copyright from my post.
If you are going to it do it right and post the hole thing and Kenney Rodgers may want part of the credit for that to.

http://www.automotiveforums.com/vbul...d.php?t=554929

Quote:
Originally Posted by chevrock22why have respect for somone who has no idea what there talking about when they think they do.

chevrock22 it is Time to hang up the crap.
Like kenney Rodgers says there is a time to fold and a time to play.
It is time for you to fold and move on will you are ahead.
If not the moderator may be along to read you you your rights.
You asked a Obenostic question and got several good answers that fits the question.
Good Luck
MT
__________________
If you are going to do it. Do it right the first time. Or you will have to undo it the next time. MT

[bracketshark]

I know that when my timing was set at the Chevy dealership my friend employed there used the hand held unit and I myself turned the distributor until he said it was on ZERO. If you think the distributor will not affect timing go to one and turn one and see what happens. I've changed a dozen or so intake gaskets on vortec motors and know for sure you better put that distributor back in the exact location it comes from. You are correct in saying the computer will make adjustments as neccessary but it must be at ZERO PLUS OR MINUS TWO DEGREES OF DISTRIBUTOR [/b]TIMING PERIOD or the check engine light will come on until corrected. The engine will run up to 16 degrees out. If you want a real challenge get the GM distributor installation procedure and try to figure IT out, if distributor location didn't matter it wouldn't be so important where it was installed.

[MT-2500]

Originally Posted by bracketshark

I know that when my timing was set at the Chevy dealership my friend employed there used the hand held unit and I myself turned the distributor until he said it was on ZERO. If you think the distributor will not affect timing go to one and turn one and see what happens. I've changed a dozen or so intake gaskets on vortec motors and know for sure you better put that distributor back in the exact location it comes from. You are correct in saying the computer will make adjustments as neccessary but it must be at ZERO PLUS OR MINUS TWO DEGREES OF DISTRIBUTOR [/b]TIMING PERIOD or the check engine light will come on until corrected. The engine will run up to 16 degrees out. If you want a real challenge get the GM distributor installation procedure and try to figure IT out, if distributor location didn't matter it wouldn't be so important where it was installed.

I hate to break the news to you but the timing can not be adjusted on the newer v6 or v8 truck engines.
If you do not believe me get out your repair manual and read it.
I know I found it hard to believe to after adjusting the timing with the dist for 45 years but read the book and see.
You can turn the dist all day and not change the timing. It is preset and not adjustable from the crankshaft sensor.
Words of wisdom and experiance from the desk of MT-2500


And From the good book.

IGNITION TIMING

NOTE: Ignition timing is controlled by control module and is not adjustable.

CAMSHAFT RETARD OFFSET

NOTE:

Distributor can be adjusted to prevent crossfire.

Checking Retard Offset
1) With ignition off, connect a scan tool to Data Link Connector (DLC). Start engine and run until normal operating temperature is reached.

NOTE: Camshaft retard offset reading will NOT be accurate with
engine speed less than 1000 RPM.

2) Increase engine speed to more than 1000 RPM. Using scan tool, monitor Cam Retard Offset. If camshaft retard indicates zero degrees plus or minus 2 degrees, distributor is properly adjusted. Procedure is complete. If camshaft retard is not zero degrees plus or minus 2 degrees, see ADJUSTING RETARD OFFSET.

NOTE: Camshaft retard offset reading will NOT be accurate with engine speed less than 1000 RPM.

Adjusting Retard Offset
1) Turn ignition off. Slightly loosen distributor hold-down
bolt. Start engine. Increase engine speed to more than 1000 RPM. 2) Using scan tool, monitor Cam Retard Offset. To adjust for
a negative reading, rotate distributor counterclockwise. To adjust for a positive reading, rotate distributor clockwise.
3) Continue to adjust as necessary until zero degrees plus or minus 2 degrees is attained. Turn ignition off. Tighten distributor hold-down bolt to 25 ft. Ibs. (34 N.m.). Start engine. Increase engine speed to more than 1000 RPM. Using scan tool, verify camshaft retard offset adjustment.


The dist does need set but.
Turning the dist only sets the camshaft retard offset
It has nothing to do with the engine timing.
What it actually does is to center the dist rotor to the spark plug terminal on the dist cap.
If it does not fire when centered on the terminal it will cause a spark jump.

[MT-2500]

Originally Posted by bracketshark

I know that when my timing was set at the Chevy dealership my friend employed there used the hand held unit and I myself turned the distributor until he said it was on ZERO. If you think the distributor will not affect timing go to one and turn one and see what happens. I've changed a dozen or so intake gaskets on vortec motors and know for sure you better put that distributor back in the exact location it comes from. You are correct in saying the computer will make adjustments as neccessary but it must be at ZERO PLUS OR MINUS TWO DEGREES OF DISTRIBUTOR [/b]TIMING PERIOD or the check engine light will come on until corrected. The engine will run up to 16 degrees out. If you want a real challenge get the GM distributor installation procedure and try to figure IT out, if distributor location didn't matter it wouldn't be so important where it was installed.

I do have the procedure for setting the dist and it is not hard to figure out.
I have set a few hundred in my time.
And yes the setting mater but it has nothing to do with the ign timing.
http://files.automotiveforums.com/ga...hp?photo=51302
Here is some more info from the repair manual on it.

IGNITION SYSTEM

Enhanced Ignition System
The enhanced ignition system consists of the VCM, distributor, ignition coil driver module, ignition coil and Camshaft Position (CMP) sensor. Ignition control and by-pass functions are controlled by the VCM.

* Camshaft Position (CMP) Sensor
CMP sensor is similar to CKP sensor. CMP sensor provides one pulse (1X signal) per camshaft revolution. VCM uses this signal in conjunction with the crankshaft position to determine which cylinder(s) are misfiring. * Crankshaft Position (CKP) Sensor
CKP sensor is located in the front engine cover. Air gap between sensor and target wheel is preset and is not
adjustable. Target wheel has 4 slots, 60 degrees apart, and is keyed to the crankshaft. Rotation of target wheel creates
a change in the magnetic field of the sensor which results in an induced voltage pulse. One crankshaft revolution will
result in 4 pulses (4X signal). Based on these pulses, VCM is able to determine crankshaft position and engine speed. VCM will then activate the fuel injector and provide spark to distributor.
* Distributor
Distributor assembly contains the Camshaft Position (CMP) sensor, cap, rotor and shaft. A Diagnostic Trouble Code (DTC) will set when distributor is installed a tooth off in
relation to the camshaft. Distributor is not serviceable. * Ignition Coil Driver Module
Module is mounted next to coil. VCM signals the ignition coil driver to turn on primary current to the ignition coil by pulling the IC line high (4 volts). The ignition control
driver turns the primary current on and off by applying and removing ground to primary winding. Module does not have a back-up function that would allow engine to run if IC signal is lost.

Ignition Timing Control
Ignition spark timing and ignition dwell time are entirely
controlled by the PCMNCM. The PCMNCM monitors information from various engine sensors, computes the dissjred spark timing and dwell, and firing of the ignition coil via IC line to the coil driver.