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GMC Forum: 1995 Sierra runs rough. Needs tune up help
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  #1  
Old 04-30-2010, 05:50 PM
sofasurfer sofasurfer is offline
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Default 1995 Sierra runs rough. Needs tune up help

runs rough. Idles bad. Accelerating, I need to pump it to get up to speed. When I stop it wants to stall. I think its starved for gas.
I checked the rotor cap. Looks good, as does the cap. I took the distrib out because I broke off a distrib cap bolt (woops). Think I put the distrib in correctly but wonder if it is off a tooth.
It starts. I checked timing. When running best, and fairly smooth, the timing doesn't even register on the timing mark plate. When properly timed it runs like hell.
I did disconnect the plug thing under the dash (advance?).
Any help appreciated.
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  #2  
Old 04-30-2010, 06:38 PM
Molson02536 Molson02536 is offline
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Originally Posted by sofasurfer View Post
runs rough. Idles bad. Accelerating, I need to pump it to get up to speed. When I stop it wants to stall. I think its starved for gas.
I checked the rotor cap. Looks good, as does the cap. I took the distrib out because I broke off a distrib cap bolt (woops). Think I put the distrib in correctly but wonder if it is off a tooth.
It starts. I checked timing. When running best, and fairly smooth, the timing doesn't even register on the timing mark plate. When properly timed it runs like hell.
I did disconnect the plug thing under the dash (advance?).
Any help appreciated.
Start with the simple and replace the fuel filter, dirty fuel filter can give you the issues you described. Here is a link for you to retrieve your DTC codes if you have not retrieved any yet. Good luck and keep me posted, be glad to help you get your Sierra running 100% again soon.

http://www.troublecodes.net/GM/
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Old 04-30-2010, 07:38 PM
sofasurfer sofasurfer is offline
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That information is too dang cool! Thanks. I'll check it out tomorrow.
I was not able to time it properly as it ran so rough when timed near correctly and the timing mark jumped around. So I timed it to sound as good as possible. At that point the timing mark is 54 degrees off. That is according the the knob at the back of the timing light. Do you understand me? I am not sure I do. It idles much better now but just once in a while wants to stall. After it sits a little while it still is very rough on take off but after a couple minutes it runs pretty smooth. It is a big improvement but still not right.
I can take this to my brother 30 miles away but I would prefer to figure it out myself...er, I mean by OURselves:-)
I'll keep you posted.
Thanks.
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Old 05-01-2010, 01:37 AM
Molson02536 Molson02536 is offline
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Originally Posted by sofasurfer View Post
That information is too dang cool! Thanks. I'll check it out tomorrow.
I was not able to time it properly as it ran so rough when timed near correctly and the timing mark jumped around. So I timed it to sound as good as possible. At that point the timing mark is 54 degrees off. That is according the the knob at the back of the timing light. Do you understand me? I am not sure I do. It idles much better now but just once in a while wants to stall. After it sits a little while it still is very rough on take off but after a couple minutes it runs pretty smooth. It is a big improvement but still not right.
I can take this to my brother 30 miles away but I would prefer to figure it out myself...er, I mean by OURselves:-)
I'll keep you posted.
Thanks.
1995 Chevy 350, you need to unplug the brown wire under the black cover on the pass side firewall. Then make sure its timed on 0 measured at the front of the damper. If it does not run right take off the dist cap and with a socket and long breaker bar have someone watch the dist rotor as you turn the engine reverse rotation, what you are looking for is a slack in the timing chain.

If their is significant slop, then re-time engine 2-4 degrees advanced till it is running good again. When you are done reconnect the brown wire and put the plastic cover back on. Done. The distributor is computer controlled. The base setting must be correct, then computer will take over from there to advance and retard timing.
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Old 05-01-2010, 05:31 PM
sofasurfer sofasurfer is offline
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I did the DTC codes check. It appears to be giving me 3 differant codes. It flashes this sequence...42,42,42,44,44,44,12,12,12...and then it repeats the same sequence over and over.
According to the code chart there is no code "12".
What can you deduce from this information?
My vehicle is a 95 GMC Sierra 5.7L with VIN "K".
Thanks.
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Old 05-01-2010, 06:15 PM
Molson02536 Molson02536 is offline
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Originally Posted by sofasurfer View Post
I did the DTC codes check. It appears to be giving me 3 differant codes. It flashes this sequence...42,42,42,44,44,44,12,12,12...and then it repeats the same sequence over and over.
According to the code chart there is no code "12".
What can you deduce from this information?
My vehicle is a 95 GMC Sierra 5.7L with VIN "K".
Thanks.
DTC code #42, check the connection to your ICM (ignition control module) at the distributor, inspect for any signs of damage like corrosion or the ICM my be on it's way out.

DTC code #44, Check your left O2 sensor wire harness, look for damages and at worst, replace your O2 sensor.

DTC code #12, means your OBD1 system is working fine and all codes given needs to be addressed.

Good luck and keep me posted.
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Old 05-01-2010, 07:38 PM
sofasurfer sofasurfer is offline
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Do I need to clear the codes before rechecking them? I mean, do I need to clear them after any repairs? How do I clear them?
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Old 05-02-2010, 01:19 AM
Molson02536 Molson02536 is offline
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Do I need to clear the codes before rechecking them? I mean, do I need to clear them after any repairs? How do I clear them?
YOU can clear the codes by disconnecting the battery for 5 min with the head lights on to make sure there is no power in the system. once you have cleared the codes after you addressed the issues, re-check for any DTC codes after your test drive.

Good luck and keep me posted, be glad to help.
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Old 05-12-2010, 12:42 AM
sofasurfer sofasurfer is offline
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I am unable to adjust my timing with a light. Timed by light, it runs real bad and dies. Timed by ear so it runs smooth (pretty smooth) and the timing mark is off by about 25 degrees.
Can the Ignition Control Module cause symptoms like this?
I have been told that the module can not be tested. But I found out today that Auto Zone says they can test it, so I will be taking it up there in a couple days.
Thanks.
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Old 05-12-2010, 08:40 AM
Molson02536 Molson02536 is offline
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Quote:
Originally Posted by sofasurfer View Post
I am unable to adjust my timing with a light. Timed by light, it runs real bad and dies. Timed by ear so it runs smooth (pretty smooth) and the timing mark is off by about 25 degrees.
Can the Ignition Control Module cause symptoms like this?
I have been told that the module can not be tested. But I found out today that Auto Zone says they can test it, so I will be taking it up there in a couple days.
Thanks.
Your engine, a TBI engine and setting the timing requires that you disconnect the EST wire near the firewall under the black wire cover. It is either black with a tan line or tan with a black line, I can never remember. It can easily be disconnected and I think it is the only wire like that under the cover.

To use a timing light there is a wire that needs to be disconnected. Usaully the underhood engine decal will show how to time the engine. The base timing should be 0į but can be advance a couple degrees. To set the timing you must unplug the set timing connector. The set timing wire, which is a single Tan wire with a black stripe/tracer on it, is located, under the hood, on the main harness that goes from the engine to the firewall, on the passenger side, sometimes underneath the black plastic cover (if itís still there) that covers the junction block, relays & fuses. Itís near the top usually on the back side of the harness. From the factory there is what looks like black tape around the harness holding the set timing wire to the back of the harness. Doing this will set a code 42 in the computer. Clear the code after you are done checking or setting the timing.


Keep me posted.
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