My truck has a slight miss! BUt NOT ALL THE TIME?? Help me out here! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

sam's 72 · 04-01-2003, 04:25 PM

I have a 305 in the truck, I did a complete tune up on it about 3 months ago, rotor, cap, wires, plugs. All new, it has been running great. Smooth, but before I did this it had a slight miss, but not all the time, and just at idle, not under a load. Well, now that slight miss is back, but it is not all the time. What I mean by this, is some days it runs very very smooth, then one day I might get in it and it pull up to a light, and there it is, it is not a constant miss either, just every now and then you can feel it. Hell, I might go a whole week with out feeling it, then all of a sudden, there it is again, I have also upgraded my chargeing system, I thought it might have been that at one time, but it's still doing it! I have a 140 amp alt, internal regulated. One wire .Sowhat doyou think it could be? I wish I could some how, exssplain better of what it is doing, but it's hard too.
Sam

Class of 69 · 04-01-2003, 04:50 PM

sam, I hear ya buudy... I have the same thing in my 95 K1500 with 350. Replaced the coil, wires, cap, rotor, and plugs. Thought the intermittent miss was gone, and a week later it came back!! Sorry I'm no help, but I know what you mean, and will be closely monitering this post for advice also. Drives ya nuckin futs doesn't it!!!

sam's 72 · 04-01-2003, 05:28 PM

class of 69,
Yeah it will drive you nuts! I don't understand this one, hell there is times when it goes away for like a month, then it's back, then it might do it everyday, for like 5 days, then it goes away, it isn't a big miss, just real slight, enough to feel it.
Sam

Gordo · 04-01-2003, 05:41 PM

The carb (assuming it's carberated) may be running a little off. How do the plugs look? What color? Are they uniform? What color does the inside of the tail pipe(s) look like?

adamls · 04-01-2003, 05:44 PM

Had the same problem on my 99, I changed the plugs and it went away. The original plugs only had 25K miles on them. I installed the new Bosch Platinum 4, hadnt had a problem in 12K miles.

sam's 72 · 04-01-2003, 05:55 PM

It is carerated, I have not pulled the plugs out since I put them in about three months ago, they don't have 5000 miles on them yet, they are Auto lite platinum. I have adjusted the carb, to where I recieve max vacuum on a gauge. Way does'nt it do it all the time? It acts like a egnition problem, but hell it does not do it constant enough to try and pin it down.
Sam

Old Paint · 04-01-2003, 09:08 PM

They stick autolites in fords don`t they? That could be your problem.

**too much stuff** · 04-02-2003, 12:05 AM

Running headers? Might want to check plug wires just to make sure they are not arcing on metal somewhere. Even if wires are new doesn't mean they are good.

Hooter · 04-02-2003, 12:15 AM

Speaking of Fords no matter what I do to my 300 straight 6 it still misses at idle, so as far as I am concerned it can miss till the cows come home.

ZOOMY · 04-02-2003, 05:26 AM

If your ignition is up to snuff, check for a vacuum leak, especially around the intake/head areas. Possibly to power brake booster.

sam's 72 · 04-02-2003, 09:17 AM

I don't have headers, I looked at this the other night, didn't see any arcing at all. Now as far as a vacuum leak, that is what I was thinking also, going to check it out this weekend, probabley change out all the hoses and see how that goes.
Sam

Blue Beard · 04-02-2003, 09:42 AM

sam's 72, I have to agree the Autolites belong in the F**ds (don't like to swear on the board)

adamls I like the Bosch plugs, I put them in my 89 Harley.

Tynee · 04-02-2003, 10:03 AM

Sam, electric or mechanical fuel pump? On my '91 w/350 I had EXACTLY the problem you are describing until the electric pump quit completely one day. After replacing pump, miss went away.

Class of '69, on your '95, you should be able to hear the pump. It'll be a real high pitched buzz coming from the behind the cab. If it sounds kinda sick or intermittent when the truck is missing, then I'd go to NAPA and get a pump for $30. Make sure you drive most of the gas out before you drop that tank, though. HEAVY.

sam's 72 · 04-02-2003, 10:38 AM

The fuel pump is mechanical, I have removed the fuel filter from the carb, and installed a inline filter.
Sam

Jesse 67 c-10 · 04-02-2003, 11:10 AM

What are your plugs gapped at? My truck was idleing poorly, pulled the plugs, one was at .06?!? regaped them all to .45, smoothed it out alot. maybe too much vac advance at idle? Good luck
Jesse

Long Knight · 04-02-2003, 01:01 PM

Mine does the same thing. Someone told me once that it could be the RV cam that I put in it, makes it harder to even out at idle. But I don't know anything about that. I think I might try that idea for checking the gap on the plugs.

Class of 69 · 04-02-2003, 11:44 PM

Tynee, I didn't feel it was fuel caused, but i may have to rethink that. The miss appears so suddenly, it's like the ignition switch is being turned off and on quickly. There have 3 times now when at a stop light , it just starts running really rough, and allmost feels like it will die. but when the light changes, and i give it throttle, it comes around again and runs smooth like nothing ever happened. Are these TBI's dependant on constant fuel pressure, unlike a float system?? The truck just turned 103 rounds, so any thing is possible. I put in the MSD Blaster coil, and Accel super stock wires, cap, and rotor. Stock AC plugs. It starts much quicker now, and runs very nice... until it starts missing!!

Tynee · 04-03-2003, 10:36 AM

Class, that sounds EXACTLY like my '91's symptoms. Had electronic diagnostics run, and they said the fuel pressure was low, probably due to a bad pump. I think the TBI's must be dependent on that constant pressure. If you've got a buddy with one of those Sun-pro scanners from Snap-On, it'll tell you what kind of pressure you're getting.

Class of 69 · 04-04-2003, 09:52 AM

Tynee, I'd have to take it to a shop for diagnosis.... may as well use the money for a new pump!! With the mileage on the truck, it won't hurt to just change it out. I'm planning on a 1600 mile parts run next week, And I don't need it dieing some where on the freeway! thanks for the help.. I hope Sams72 got some help from HIS thread!!??

*dtlilly* · 04-04-2003, 10:23 AM

CO69, I replace a lot of GM fuel pumps, some even at 80,000 ticks. I would also look at the TPS. Also clean the fuel injectors and the valves.

Blue68 · 04-04-2003, 04:49 PM

Are you still running points? The dwell has a tendency to not stay set very long.

MandarinSixSeven · 04-04-2003, 05:12 PM

Could be the Idle circuit in your carb is dirty, try cleaning the carb really well, this happened to me before, same sort of thing.

sam's 72 · 04-11-2003, 11:29 AM

I posted this last week, I have not done anything to the truck, and now this week, it is running smooth as silk! I don't understand why it does this, makes me think that I might be getting bad gas, maybe a little water in it.
Hell, I don't know!
Sam

*dtlilly* · 04-11-2003, 11:43 AM

Sam,

It just warmed up by you didn't it? Your choke might be off, and when it's cold, you could be rich, causing the plugs to foul out. When it warms up, the plugs clean up, and runs well. Sure sounds like that, or a secondary ignition problem of sorts.

sam's 72 · 04-11-2003, 11:50 AM

No, it does it after it has been warmed up, I can drive it 30 miles and sometimes this miss is there. But this week, it is running smooth. This has been going on for a while now, every since i bought the truck, and the miss is not constant, it is very slight.
dtlilly, what do you mean by secondary ignition problem of sorts.
What can I look for?
Sam

04-01-2003, 04:25 PM	#1
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	My truck has a slight miss! BUt NOT ALL THE TIME?? Help me out here! I have a 305 in the truck, I did a complete tune up on it about 3 months ago, rotor, cap, wires, plugs. All new, it has been running great. Smooth, but before I did this it had a slight miss, but not all the time, and just at idle, not under a load. Well, now that slight miss is back, but it is not all the time. What I mean by this, is some days it runs very very smooth, then one day I might get in it and it pull up to a light, and there it is, it is not a constant miss either, just every now and then you can feel it. Hell, I might go a whole week with out feeling it, then all of a sudden, there it is again, I have also upgraded my chargeing system, I thought it might have been that at one time, but it's still doing it! I have a 140 amp alt, internal regulated. One wire .Sowhat doyou think it could be? I wish I could some how, exssplain better of what it is doing, but it's hard too. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-01-2003, 04:50 PM	#2
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	sam, I hear ya buudy... I have the same thing in my 95 K1500 with 350. Replaced the coil, wires, cap, rotor, and plugs. Thought the intermittent miss was gone, and a week later it came back!! Sorry I'm no help, but I know what you mean, and will be closely monitering this post for advice also. Drives ya nuckin futs doesn't it!!! __________________ 69 GMC K10 ..some restoration required....still..

04-01-2003, 05:28 PM	#3
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	class of 69, Yeah it will drive you nuts! I don't understand this one, hell there is times when it goes away for like a month, then it's back, then it might do it everyday, for like 5 days, then it goes away, it isn't a big miss, just real slight, enough to feel it. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-01-2003, 05:41 PM	#4
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	The carb (assuming it's carberated) may be running a little off. How do the plugs look? What color? Are they uniform? What color does the inside of the tail pipe(s) look like? __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

04-01-2003, 05:44 PM	#5
adamls Gotta Startem Early Join Date: Oct 2001 Location: Amarillo, TX, USA Posts: 364	Had the same problem on my 99, I changed the plugs and it went away. The original plugs only had 25K miles on them. I installed the new Bosch Platinum 4, hadnt had a problem in 12K miles. __________________ 67 SWB In Progress, one piece at a time, maybe 3 years I will be finished

04-01-2003, 05:55 PM	#6
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	It is carerated, I have not pulled the plugs out since I put them in about three months ago, they don't have 5000 miles on them yet, they are Auto lite platinum. I have adjusted the carb, to where I recieve max vacuum on a gauge. Way does'nt it do it all the time? It acts like a egnition problem, but hell it does not do it constant enough to try and pin it down. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-01-2003, 09:08 PM	#7
Old Paint Registered User Join Date: Mar 2002 Location: Fairdale, Kentucky Posts: 46	They stick autolites in fords don`t they? That could be your problem.

04-02-2003, 12:05 AM	#8
too much stuff Roadtrip! Join Date: Feb 2003 Location: Grand Rapids MN Posts: 13,713	miss Running headers? Might want to check plug wires just to make sure they are not arcing on metal somewhere. Even if wires are new doesn't mean they are good.

04-02-2003, 12:15 AM	#9
Hooter My other Love Join Date: Aug 2001 Location: Castlegar B.C. Canada Posts: 4,085	Speaking of Fords no matter what I do to my 300 straight 6 it still misses at idle, so as far as I am concerned it can miss till the cows come home. __________________ Castlegar B.C.The great white North (Canada Eh!) Hooter_5@hotmail.com First generation Monte Carlo club pictures of my life

04-02-2003, 05:26 AM	#10
ZOOMY Senior Member Join Date: Feb 2003 Location: WIS Posts: 1,752	miss If your ignition is up to snuff, check for a vacuum leak, especially around the intake/head areas. Possibly to power brake booster.

04-02-2003, 09:17 AM	#11
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	I don't have headers, I looked at this the other night, didn't see any arcing at all. Now as far as a vacuum leak, that is what I was thinking also, going to check it out this weekend, probabley change out all the hoses and see how that goes. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-02-2003, 09:42 AM	#12
Blue Beard Registered User Join Date: Jan 2003 Location: Washington State Posts: 8,834	sam's 72, I have to agree the Autolites belong in the Fds (don't like to swear on the board) adamls I like the Bosch plugs, I put them in my 89 Harley. __________________ 1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00** 1978 Silverado 2005 Monte Carlo

04-02-2003, 10:03 AM	#13
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	Sam, electric or mechanical fuel pump? On my '91 w/350 I had EXACTLY the problem you are describing until the electric pump quit completely one day. After replacing pump, miss went away. Class of '69, on your '95, you should be able to hear the pump. It'll be a real high pitched buzz coming from the behind the cab. If it sounds kinda sick or intermittent when the truck is missing, then I'd go to NAPA and get a pump for $30. Make sure you drive most of the gas out before you drop that tank, though. HEAVY. __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.

04-02-2003, 10:38 AM	#14
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	The fuel pump is mechanical, I have removed the fuel filter from the carb, and installed a inline filter. Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-02-2003, 11:10 AM	#15
Jesse 67 c-10 Registered User Join Date: Feb 2000 Location: Edmonton, Alberta, Canada Posts: 599	What are your plugs gapped at? My truck was idleing poorly, pulled the plugs, one was at .06?!? regaped them all to .45, smoothed it out alot. maybe too much vac advance at idle? Good luck Jesse __________________ Edmonton, Alberta, 67 c-10, Long fleet, front disks, 5 lug rear end, 327 with Vortechs, edlbrock manifold, comp cams XE 256, 600cfm carb. Backed by a getrag 5 speed and 1 piece driveshaft. 1993 Dihatsu Hijet Jumbo cab 4x4, currently converting to battery electric power.



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04-02-2003, 01:01 PM	#16
Long Knight Spank 'em if you got 'em! Join Date: Nov 2002 Location: Kansas City Posts: 628	Mine does the same thing. Someone told me once that it could be the RV cam that I put in it, makes it harder to even out at idle. But I don't know anything about that. I think I might try that idea for checking the gap on the plugs. __________________ Long Knight '71 C-20, 350ci, TH350, Edl. 1406 Carb w/elec.choke, Ignitor ignition, Viper Tires, Orange Dipstick

04-02-2003, 11:44 PM	#17
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	Tynee, I didn't feel it was fuel caused, but i may have to rethink that. The miss appears so suddenly, it's like the ignition switch is being turned off and on quickly. There have 3 times now when at a stop light , it just starts running really rough, and allmost feels like it will die. but when the light changes, and i give it throttle, it comes around again and runs smooth like nothing ever happened. Are these TBI's dependant on constant fuel pressure, unlike a float system?? The truck just turned 103 rounds, so any thing is possible. I put in the MSD Blaster coil, and Accel super stock wires, cap, and rotor. Stock AC plugs. It starts much quicker now, and runs very nice... until it starts missing!! __________________ 69 GMC K10 ..some restoration required....still..

04-03-2003, 10:36 AM	#18
Tynee I miss this truck. Join Date: Dec 2001 Location: Lexington, KY U.S.A. Posts: 2,863	Class, that sounds EXACTLY like my '91's symptoms. Had electronic diagnostics run, and they said the fuel pressure was low, probably due to a bad pump. I think the TBI's must be dependent on that constant pressure. If you've got a buddy with one of those Sun-pro scanners from Snap-On, it'll tell you what kind of pressure you're getting. __________________ '07 GMC Acadia SLT. Sweet ride. '08 Crew Cab Z-71 short bed. Really like this truck A LOT.

04-04-2003, 09:52 AM	#19
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	Tynee, I'd have to take it to a shop for diagnosis.... may as well use the money for a new pump!! With the mileage on the truck, it won't hurt to just change it out. I'm planning on a 1600 mile parts run next week, And I don't need it dieing some where on the freeway! thanks for the help.. I hope Sams72 got some help from HIS thread!!?? __________________ 69 GMC K10 ..some restoration required....still..

04-04-2003, 10:23 AM	#20
dtlilly Account Suspended Join Date: Jan 2003 Location: Shadow of Lambeau Field Posts: 5,597	CO69, I replace a lot of GM fuel pumps, some even at 80,000 ticks. I would also look at the TPS. Also clean the fuel injectors and the valves.

04-04-2003, 04:49 PM	#21
Blue68 Registered User Join Date: Apr 2000 Location: Frisco, Tx, USA Posts: 606	Are you still running points? The dwell has a tendency to not stay set very long. __________________ http://home.comcast.net/~r.landrum/w...tos.html-.html '68 C-10 LWB, '98 Z-71 350 w/accessories (Serpentine), Edelbrock Performer, Edelbrock 1405 (600cfm) carb, GM HEI, CompCam Extreme 4x4 roller cam, Thorley Headers, Carter Electric Fuel Pump, Vintage Air, 700r4, 3.73, disc brakes and power steering upgrades.

04-04-2003, 05:12 PM	#22
MandarinSixSeven Seasonal Poster Join Date: Apr 2002 Location: Kelowna BC Canada Posts: 896	Could be the Idle circuit in your carb is dirty, try cleaning the carb really well, this happened to me before, same sort of thing. __________________ 67 GMC Short Step 350/4-Speed/3.08 Posi Front/Rear Sway Bars Kelowna BC, Canada Member of DTPW

04-11-2003, 11:29 AM	#23
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	I posted this last week, I have not done anything to the truck, and now this week, it is running smooth as silk! I don't understand why it does this, makes me think that I might be getting bad gas, maybe a little water in it. Hell, I don't know! Sam __________________ 72 LWB chevy truck. Pasadena, Texas

04-11-2003, 11:43 AM	#24
dtlilly Account Suspended Join Date: Jan 2003 Location: Shadow of Lambeau Field Posts: 5,597	Sam, It just warmed up by you didn't it? Your choke might be off, and when it's cold, you could be rich, causing the plugs to foul out. When it warms up, the plugs clean up, and runs well. Sure sounds like that, or a secondary ignition problem of sorts.

04-11-2003, 11:50 AM	#25
sam's 72 Senior Member Join Date: Nov 2001 Location: Pasadena, Texas, USA Posts: 1,005	No, it does it after it has been warmed up, I can drive it 30 miles and sometimes this miss is there. But this week, it is running smooth. This has been going on for a while now, every since i bought the truck, and the miss is not constant, it is very slight. dtlilly, what do you mean by secondary ignition problem of sorts. What can I look for? Sam __________________ 72 LWB chevy truck. Pasadena, Texas

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