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Username Post: 99 GM 5.7L misfire        (Topic#159786)
bshir 
Member
Posts: 7

Reg: 05-16-07
05-16-07 05:58 PM - Post#1166362    

99 GMC Yukon 5.7 with P0300 misfire code and hesitation upon moderate to light acceleration or constant speed. Hesitation goes away upon rapid acceleration.

Replaced: plugs, wires, rotor, dist cap, fuel pump, fuel filter, #6 Cyl injector. Also had injectors flushed, tested coil (good), verified ignition control unit (good), compression tested 1-8 (good), vacuum check (good).

New #6 spark plug covered in soot (running rich). Observed #6 spark plug operation with plug out of engine; operated fine at idle, however missing spark upon increased RPM and spark gone during quick and heavy RPM. Spark returned upon contant RPM or idle.

Swapping cables or other hardware made no change. Problem stayed at cyl #6.

Everythings points to an electrical problem but I am at wits end, I even stump the dealer service department. I have looked at many forums and seen similair problems but no positive fix actions.

 
CaptainK 
Senior Member
Posts: 8242
CaptainK
Loc: Maryland
Reg: 02-25-02
05-17-07 04:07 AM - Post#1166576    
    In response to bshir

Welcome to the site!!

I am going to shoot this over to the 88-98 truck forum since this is an old body style 99. Should get more assistance over there.
'99 Silverado (NBS)


 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
05-17-07 04:29 AM - Post#1166591    
    In response to bshir

I suppose you have changed intake gaskets? Probably 60-70% of the #6 misfires heard of here can be determined by following this thread. Look for chevysilverados first post.

Basically, the intake gasket draws into the intake valley. The later gaskets have a reinforcement to prohibit this.

 
bshir 
Member
Posts: 7

Reg: 05-16-07
05-17-07 05:55 AM - Post#1166654    
    In response to CDAUSA

Yes the intake gasket was changed when I changed the #6 injector. I continue to lean toward electrical because of loss of spark as I discribed. Do you think the way I tested the spark is inaccurate or scued?



 
bshir 
Member
Posts: 7

Reg: 05-16-07
05-17-07 05:56 AM - Post#1166655    
    In response to CaptainK

Thank you, thought the 99-06 seemed wrong.

 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
05-17-07 06:13 AM - Post#1166673    
    In response to bshir

What were you using to test fire to the plug?

If it in fact is losing fire, and only #6, I would first pull the cap and check the distributor shaft for wear------try to move it from side to side, should be zero clearance or near it. Double check the cap for carbon tracking and take off the rotor to make sure it isn't trying to burn thru.

Next, check grounds, body grounds to the engine and you should have two on the thermostat housing, are they in good shape?

Does it have 41-932 AC plugs in it?

But the test referenced above in the link, is painless and takes but a few seconds to perform.

 
bshir 
Member
Posts: 7

Reg: 05-16-07
05-17-07 05:37 PM - Post#1167201    
    In response to CDAUSA

To test the spark I pulled #6 plug wire, left the plug in the motor, connected an old ACdelco plug into the wire, lodged it agaist the dipstick and block and started the engine. Good spark until I increased RPMs then the spark is intermitent and is worse the quicker and higher the RPMs. To the point of visually being gone until the RPMs stabalize.

I originally put in after market wires and dist cap, with Bosch Platinum plugs.

I swapped out the wires and cap today with ACDelco parts.

No improvement. I tested #8 in the exact same fashion with the same plug and never lost spark. Also tested 5 & 7 all good.

Still stumped.


 
bshir 
Member
Posts: 7

Reg: 05-16-07
05-17-07 09:11 PM - Post#1167361    
    In response to bshir

Also the distributor was solid side to side. The rotor rotated a little back and forth. About an inch or so swing.


 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
05-17-07 09:25 PM - Post#1167372    
    In response to bshir

An inch, you sure an inch? That sounds like too much, some of these and there is no way to find out without pulling the distributor, wore the distributor gears badly. They just weren't hardened for the steel shaft (cam) as they should have been. Though, unless it is kicking back at the right point every time this would not affect one cylinder like this.

This subject came up late last year and I checked mine, I don't think it had quite 1/2" of rotation.

I'll throw this out there and you do with it as you please, I can name you 4 shops near here that won't start to evaluate a drivability issue on a Vortec 350 unless is has AC Plats in it, nor will I.

Thinking back, I can remember one coil that caused an issue similar in all the time I have been here, also make sure the wire is not touching anything else.

And humor me, it takes but a second, check vacuum on the dipstick tube like is suggested in that link I gave.

And, when you did everything else, did you put a new fuel regulator in? What is your fuel pressure now? This is also the cylinder nearest the fuel regulator that when it starts leaking, it can overfuel that cylinder. Easy to see though, just pop off the TB and use a good light, it's right there behind the TB port.

 
Trevor350 
Senior Member
Posts: 744
Trevor350
Age: 26
Loc: Georgetown/College Statio...
Reg: 01-25-06
05-17-07 09:39 PM - Post#1167379    
    In response to CDAUSA

Hey Steve can I do the Vaccuum test to my truck? And do I have to have a Vac. Gauge or can i just use a piece of paper?
Not trying to hijack the thread, just doing some more troubleshooting

Thanks
2007 Summit White SCSB Silverado
3" BL
2.5" CCM
305-70-17 Terra Grapplers
Magnaflow


 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
05-17-07 10:01 PM - Post#1167383    
    In response to Trevor350

Sure, easy to do.

 
Trevor350 
Senior Member
Posts: 744
Trevor350
Age: 26
Loc: Georgetown/College Statio...
Reg: 01-25-06
05-17-07 10:05 PM - Post#1167384    
    In response to CDAUSA

Alright cool so i just undo the PCV valve and the other thing off the other valve cover, plug them, take out the oil dipstick, start the truck up, put a piece of paper over the oil dipstick tube, and if i get suction its a bad intake gasket? seems easy enough

Thanks
2007 Summit White SCSB Silverado
3" BL
2.5" CCM
305-70-17 Terra Grapplers
Magnaflow


 
bshir 
Member
Posts: 7

Reg: 05-16-07
05-17-07 10:13 PM - Post#1167393    
    In response to CDAUSA

I will try your suggestions soon. To include verifying the slop in the rotor rotation, the inch was a guess. Is that the wear you were talking about in the distributor gears?

I am willing to try the AC plats but it is strange that I only have the problem in one cyl.

Could the PCM or ECM cause this kind of problem?

 
V20 
Member
Posts: 5

Reg: 05-15-07
05-18-07 10:27 AM - Post#1167702    
    In response to bshir

I had virtually the same thing happen on a 96 with 5.7. It all started 4-5000 miles after I had put Bosch plugs in. The only thing different was I had 2 cylinders #3 and #7 misfiring. The only plug to use is AC. I spent alot of money and time finding out it was somthing I had done. I have since seen the same thing on 3 other GM trucks with 5.7's.

 
chopperguy234 
Member
Posts: 61
chopperguy234
Loc: Minnesota
Reg: 12-01-06
05-18-07 04:24 PM - Post#1167908    
    In response to V20

the plugs are a huge deal in these engines, my 97 with the 5.7 wouldn't rev higher then 3000, wouldn't miss or cut out or anything, i had ac plugs in it and put a new set in it and it fixed the problem. i wouldn't put anything else in it besides the ac plugs.

chopperguy
97 K1500 Z71, some mods
99 Jeep Wrangler, 4 Inch Lift
94 Bayliner 2858


 
bluechevy93 
Senior Member
Posts: 126
bluechevy93
Age: 43
Loc: Oklahoma City, OK
Reg: 05-11-07
05-18-07 04:59 PM - Post#1167930    
    In response to chopperguy234

Does the same apply to the 93 350 TBI engines? I have Bosch Platinums in there right now. Are they as sensitive as the later models?
2009 Dodge Ram Crew Cab 1500 4x4
5.7L / V-8 / Automatic
1,500 miles

2007 Chevrolet Avalanche LS 4x2
5.3L / V-8 / Automatic
27,000 miles

SOLD - 93 Chevy K1500


 
chopperguy234 
Member
Posts: 61
chopperguy234
Loc: Minnesota
Reg: 12-01-06
05-18-07 10:19 PM - Post#1168110    
    In response to bluechevy93

i don't think the TBI engines are, i use to have a 90 that burned oil something terrible, although the bosch platinums i put in that made it run better over just the regular plugs that those engines ran
97 K1500 Z71, some mods
99 Jeep Wrangler, 4 Inch Lift
94 Bayliner 2858


 
bshir 
Member
Posts: 7

Reg: 05-16-07
05-20-07 10:39 AM - Post#1168957    
    In response to CDAUSA

Found the problem and fixed.

The distributor gear was worn down so far the teeth were razor sharp and chiping away.

Replaced the gear and everything is working great. However, it wasn't that easy: I snapped the heater hose connection off with my foot while reinstalling the ditributor. It was flush with the lower intake manifold. Had to remove the manifold and chisel out the broken piece. Now that was a bear!

I have learn more about the 5.7L than I care to let in this brain, but I owe this success to people like you both in forums and at various parts stores and auto shops.

Cheers to those that help the novice mechanics.


Thanks again





 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
05-20-07 10:52 AM - Post#1168963    
    In response to bshir

Sorry you had to go thru that but glad you got it fixed----unless we start compiling a database as to when the engines were put online we just don't know when those gears were done.

I do wish you had read the many fixes for the heater hose fitting before pulling the intake, most are listed above in the searching for info sticky. Usually takes about 15 minutes to do.

Congrats on getting it done yourself

 
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