Head or Lower Intake Gasket?

[1998Suburban]

There's a TSB for a P0300, espec when the engine is under load (towing, pulling a hill, etc.). The fix is to pull the heads and ream the valve guides per the TSB. For as often as it occurs on my '98 I said to heck with that. I'll see if I can find the TSB #.

 

[1998Suburban]

Engine - SES Lamp ON/Misfire DTC' Set Towing Uphill

Subject: SES Light and P0300 When Towing, Cruising Uphill or on hard

Acceleration - kw 4.3, 5.0, 5.7 accelerate cruise cylinderhead DTC L30, L31, L35,

LF6, LU3, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307 P0308 #

PIP3081 - (07/23/2004)

Models:

The following diagnosis might be helpful if the vehicle exhibits the symptom

described in the PI.

Condition/Concern:

The vehicle may exhibit a SES Light due to a P0300 and misfire. If the misfire is

related to the information below, it will typically happen while cruising uphill, pulling

a trailer or on hard acceleration and then stop misfiring shortly after returning to an

idle. Typically, cylinders 3, 4, 5 or 6 will be the ones to experience this.

Recommendation/Instructions:

If the P0300 SI diagnostics did not isolate a concern, the following may help:

Remove the valve cover, valve springs and valve seals on the effected cylinder or

cylinders. A small wire tie or rubber bands can be placed in the valve stem keeper

groove to prevent the valve from falling into the cylinder. Rotate the valve while

moving it up and down in the guide to see if it binds. If a binding valve is found,

remove both cylinder heads and use either of the following methods to increase

the stem to guide clearance:

Reassemble the cylinder heads using new valve seals.

Please follow this diagnosis process thoroughly and complete each step. If the

^ Send the head out to a machine shop and advise them to increase the valve

stem to guide clearance to 0.002 inch per guide.

^ Hone the guide with a 9 mm hone, such as Snap On BCG249, until a clearance

of 0.002 inch is obtained. This will usually take about 4 strokes of the hone

 

[floater]

Before I take it all apart again i'm heading out to grab a Snap On MT2500 for a good price to set that cam retard. If that fails to correct the P0300 next will be a feul filter. After doing all this work I did notice allot of water coming out of the exhaust pipes. A bit of steam too. More than it ever did. Could this be due too it sitting for over a week not running and the outside temp went up making condensation in the exhaust? I will post back when I score this scan tool and set the cam.

 

[1998Suburban]

The MT2500 is a great scan tool. Make sure you get all the personality keys with it. The FastTrack cartridges are a "nice to have" but the keys are, well, key.

 

[floater]

Well I went and did it now. I got the Snap On and hooked it up. My Cam Retard was at -11. I set it to zero and the truck ran even worse. I figured I was off a tooth on the distributor so I moved it counter clockwise and that was bad. I moved it back clock wise two teeth and that was bad. Well as I scrolled through the menu on the Snap on i saw the crank Cam relearn. I figured what could it hurt since I put in a new distributor! I throttled up to 4000 and the Snap on said it was only doing 3600 rpm. Soooo I gave it a bit more gas and Boooooom!! There was a bad noise and the truck died. I managed to get it going again but now there was a knocking coming from the drivers side bottom end. I unhooked it all today and tomorrow it gets pulled and is going to the re-builder.

I'm at my wits end now. What happens if it comes back and still does the random misfire??? If this happens I'm gonna replace the Spider injector. Uggggh

 

[1998Suburban]

Yikes! Any idea what gave out? Prior to starting this odyssey had you been north of 3500-4000 RPM? I'd be curious to see what happened.
You're having it rebuilt locally, right? Maybe you can ask the builder for a few pics of anything he finds.

 

[floater]

Never had it higher than 3000 rpm on the highways. I can't wait to hear what may have gone on it. I'm going to give the rebuilder my camera and ask him to take pics of it all. He may even let me watch the tear down.

 

[floater]

I think I'm gonna stroke out when I get the final bill for rebuilding this motor. Crank is junk. block needed to be line honed. New injectors along with all the other parts I've bought including water pump, rad and what not. Now they are telling me there was excessive wear on the main thrust bearing caused by too much pump pressure from the tranny! Waaaaaaaaaaaa

 

[drakon543]

You could probably buy a lowish miles used motor cheaper than this is going to cost you. But your already in pretty deep with this job. Best thing i could tell ya now is the bright side, as long as this shop thats doing your engine knows what they are doing and you maintain it well from this point on you will probably get tired of the truck long before the engine ever lets you down again.

 

[1998Suburban]

Wow. Incredible that it had all these engine issues and was still running decent until the end. Shop have any idea what the "boom" was?