1999 GMC Suburban K1500 5.7L misfire

[BigBadBlazer]

Hello all.

I am new to the forum. I had to choose the Yukon, as there is no Suburban?!?

Anyway, I have a very bad misfire in my truck. Lopes at idle, stumbles under load. Through substitution, I have tested: module, coil and crank sensor. I have replaced: plugs, wires, cap, rotor, air filter, fuel filter and upgraded from SCFI to MFI (can you say "expensive best guess"?).

Still getting P-0300, P-0302 and mostly P-0304, using a Snapon Modis scanner.
Compression tested today: all cylinders between 160- & 170 psi. After this, leak-down seemed redundant.
Back pressure test: 0.5 psi at 2500 RPM, both banks.
Steady fuel at about 60 psi.

Having read similar posts here, I am going to pull distributor (175K miles) and examine drive gear. Not too sloppy at rotor bearing.

However, how do I set baseline timing when I re-install distributor?

If distributor is OK, what test or part should I look at next? I will post my results of the distributor condition as soon as I know it.

Thank you,

[gmtech1]

Test Procedure


You cannot adjust the ignition timing. You may need to adjust the distributor in order to prevent crossfire. To insure proper alignment of the distributor, perform the following:

1. With the ignition OFF, connect the scan tool.
2. Start the engine. Allow the engine to idle until the engine reaches the normal operating temperature.
Important: The Cam Retard Offset reading will not be accurate below 1,000 RPM.
3. Increase the engine speed to 1,000 RPM while performing the following steps.
4. Use the scan tool in order to monitor the Cam Retard Offset.
5. If the Cam Retard indicates a value of 0 degrees, the distributor is properly adjusted.
6. If the Cam Retard does not indicate 0 degrees, the distributor must be adjusted.

Adjustment Procedure

1. With the engine OFF, slightly loosen the distributor hold down bolt.
Important: The Cam Retard Offset reading will not be accurate below 1,000 RPM.
2. Start the engine and raise the engine speed to 1,000 RPM.
3. Use the scan tool in order to monitor the Cam Retard Offset.
4. Rotate the distributor as follows:
• To compensate for a negative reading, rotate the distributor in the counterclockwise direction.

• To compensate for a positive reading, rotate the distributor in the clockwise direction.

5. Repeat step 4 until 0 degrees is obtained.
6. Turn OFF the ignition.

Notice: Refer to Fastener Notice in Cautions and Notices.

7. Tighten the distributor hold-down bolt.

Tighten
Tighten the bolt to 3 N·m (25 lb ft).

8. Start the engine.
9. Raise the engine speed to 1,000 RPM and view the Camshaft Retard Offset.

[BigBadBlazer]

Gmtech1, thank you for the info.

I am wondering though, the "Fastener Notice", when I open the link, it states "You are not authorized to view the requested information" and I am signed in. Any idea why?

Be back later with results.

[gmtech1]

The "fastener notice" just says to make sure your bolts are clean and dry when reinstalling, put back in the correct place and properly torqued.

[BigBadBlazer]

Oh. lol Thanks.

[BigBadBlazer]

Hello all,

When I removed the OE distributor with 175K miles on it, the driven gear was worn to the point the edges were sharp. This is not like other worn distributor gears I have seen, that are concaved. Apparently, the concaved wear is from improper installation - there is insufficient play between oil pump and distributor gear. Regardless, my gear was worn, so I bought a brand new, billet aluminum distributor.

Well I just installed my new Performance Distributors, distributor. I set the cam retard to 0 and double checked it. Changed to +1 after tightening distributor down, but since it is within spec, I left it alone. Sweet. Unfortunately, it still runs like crap. I cleared all codes and drove it until the check engine light came on. The only code is a P0300, general misfire.

I am thoroughly stumped. What else could be causing this misfire? A friend and former GM mechanic suggested a seemly unrelated sensor could be causing the issue. He suggested the MAF and/or MAP sensor, but I have already spent $700.00 in just parts and my wife is a little angry, to say the least!!

Anyone have any other suggestions that could be causing this? If you look over my first post, you will see parts replaced, parts tested via substitution and tests performed. Any suggestions/guidance will be greatly appreciated.

Thank you,

Mike

[bobertfrancy]

This is an old post. Did you ever figure this out?

[BigBadBlazer]

Originally Posted by bobertfrancy

This is an old post. Did you ever figure this out?

The first part I replaced, the distributor cap, a black cap with brass terminals by Accel, failed on the seventh day. Being an Accel, I could not imagine the brand new cap was the problem nor did anyone else who tried to help me figure it out what it was. However, after doing some deeper research, I will never use a black, crab-style GM distributor cap again (or anything from Accel - all three parts I have ever purchased died very quickly, but I digress). Apparently the problem is primarily the color. In order to make plastic black, the colorant is black carbon. Carbon is conductive so while the cap needs to prevent arching, the colorant encourages it. Dumb, IMHO anyway. I now only use non-black caps and only from Performance Distributors, makers of the DUI ignition system, if you're familiar. They cost less, have brass terminals and last longer. The experience of others may be different, but this is what happened in my situation.

[bobertfrancy]

Thank you for your reply. Glad you got it figured out. Seems most with similar or same issues never get solved. I ran across someone that had a car talk show at one time and he said since my gas tank pressure sensor is out or giving code I have to deal with it first before moving on as this trumps everything else. I have high white deposits on plugs when I changed yesterday. Now I'm reading fuel injection system would be best to convert to help with MPG and all above. I'm getting it running as smooth as I can and selling for $2500. Runs pretty good when not idle. Only thing I get is hard shift once in a while. Turn key off and back on and its good. Didn't realize this was going to be money pit. Glad you got yours figured out.