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#1 |
Registered User
Join Date: Apr 2002
Location: Manitoba, Canada
Posts: 663
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Truck Hesitates at 50mph - Coil?
I've got a '69 GMC with an inline 6. When I take the truck on the highway it works well, accelerating to speed. BUT when I get to 50 mph, that's it. It hesitates and will not accelerate further. It feels like an electrical problem because otherwise it drives well, but it could be fuel.
I've replaced the plug wires, distributor cap, rotor, points and condenser with no change. What next? As a related issue, the coil on the truck seems to have an additional condenser attached. I've never seen this, so I was wondering if someone could explain.
__________________
Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said. |
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#2 |
Registered User
Join Date: Dec 2006
Location: Porter Ranch, CA
Posts: 978
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Re: Truck Hesitates at 50mph - Coil?
Buy a Pertronix Ignitor II coil and the part that replaces the points in the distributor. It will be the cheapest and best thing you could do to an old engine. If that doesn't solve it, replace the fuel pump and/or clean out the ol' carbatuter...
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#3 |
Senior Member
![]() Join Date: Dec 2006
Location: Studio City, Calif.
Posts: 2,873
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Re: Truck Hesitates at 50mph - Coil?
First thought is plogged fuel filter.Check that and if no improvement check that coil if you have a meter.They do go out. You could pull a plug wire off and hold it close to ground (or use a sparkplug held up against the intake mani,etc.) and see if the spark is real good. If a feeble spark,maybe replace the coil and the capacitor ( I think that's what that is,can't remember).
__________________
'69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme. |
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#4 |
Moderator
![]() Join Date: May 2007
Location: Southern Cal
Posts: 20,006
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Re: Truck Hesitates at 50mph - Coil?
That additional part on your coil is to reduce noise heard through the radio. I have never seen it on the coil before...usually it is on the regulator.
__________________
1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man |
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#5 |
classic=of recognized value
Join Date: Sep 2008
Location: Wichita, KS
Posts: 317
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Re: Truck Hesitates at 50mph - Coil?
Is your vacuum advance working?
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#6 |
Old Skool Club
![]() Join Date: Jun 2001
Location: Benton, AR "The Heart of Arkansas"
Posts: 10,880
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Re: Truck Hesitates at 50mph - Coil?
I've seen 'em on the coils.
My experience with coils that are suspect is limited to having a bad coil wire, which breaks down just like turning off the key (under load). If it isn't leaking or you can see it arcing (in the dark), I'd think it is okay if the engine will run. You could try the Pertronix route or look for an HEI from an in-line 6, if you want to get away from what you have.
__________________
Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was. |
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#7 |
I am a Referee of life.
Join Date: Jun 2000
Location: Greensboro N.C.
Posts: 13,993
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Re: Truck Hesitates at 50mph - Coil?
I'll say HEI all the way.I couldn't believe the difference it made from my well tuned points dist to the HEI.It was a simple swap also.Here's everything you need to know to do it in an hour or so after you have the parts.Make sure you have a cold one handy since you'll have time for it,if you follow the directions exactly.
http://67-72chevytrucks.com/vboard/s...d.php?t=148346 Just so you know,I bought a coil in cap unit complete from the local "Pick and pull" for $40.00 a set of wires and new plugs.IIRC total for the swap was about $75.00, but I could have probably gotten by with the plugs I had.The coil,module and cap were in good shape so I got lucky.I would probably had a few more $$$'s in it if I had to replace any of them.
__________________
The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil" Last edited by PanelDeland; 05-29-2009 at 04:46 PM. |
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#8 |
Senior Member
![]() Join Date: Dec 2006
Location: Studio City, Calif.
Posts: 2,873
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Re: Truck Hesitates at 50mph - Coil?
Really though,before throwing a bunch of parts at it,check the fuel filter,then TEST the coil.
A properly functioning and maintained points ignition will work just fine.
__________________
'69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme. |
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#9 | |
just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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Re: Truck Hesitates at 50mph - Coil?
I am with the fuel filter guys on this one. What kind of RPM are we talking here?
The extra thing on your coil is the radio interference supressor. I have seen a lot of them mounted to the coil, but it's another thing that you can eliminate by swapping to HEI. Like Workinlonghorn said, points will work fine, they just need more attention than HEI parts.
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#10 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: Truck Hesitates at 50mph - Coil?
this sounds like a classic fuel issue, not electrical.
At 3000 RPMs in second gear, the fuel consuption is less, than 3000 RPMs in 3rd gear due to the engine working harder to overcome the wind resistance. Since the complaint is described as "problems at 50 MPH" and not "problems at 2800 RPM", it points to a fuel related issue. I would replace the fuel filter(s), and clean the carb with some gumout or berryman's B12 chemtool carb cleaner, and see what happens. |
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#11 |
Senior Member
![]() Join Date: Dec 2006
Location: Studio City, Calif.
Posts: 2,873
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Re: Truck Hesitates at 50mph - Coil?
I give up.
__________________
'69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, stereo speakers, 2nd owner, Work-Truck supreme. |
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#12 |
Moderator
![]() Join Date: May 2007
Location: Southern Cal
Posts: 20,006
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Re: Truck Hesitates at 50mph - Coil?
__________________
1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man |
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#13 |
Registered User
Join Date: Feb 2007
Location: west coast
Posts: 3,374
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Re: Truck Hesitates at 50mph - Coil?
One more fuel filter to check.Some fuel tank sending units have a filter on the end of the pickup tube.
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#14 |
Six in a row makes it go...
![]() Join Date: Mar 2009
Location: Vacationland: Maine
Posts: 1,346
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Re: Truck Hesitates at 50mph - Coil?
Just something to check:
I had a '70 Bel Air with a 250 and points. The engine would die at high rpm. Long story short - the resistor wire was not working right. A points coil requires 7 volts. If it gets too much voltage it doesn't work. Mine would see 7 volts at lower rpm, but when the engine spun, it would get 12 volts. I solved it by slamming an HEI in there. Problem solved. ![]()
__________________
67 C20 long step resto: http://67-72chevytrucks.com/vboard/s...d.php?t=342086 66 C10 long step build: http://67-72chevytrucks.com/vboard/s...=1#post3814790 CT to Alaska in a 67 C10: http://67-72chevytrucks.com/vboard/s...d.php?t=399224 “The height of sophistication is simplicity." - Clare Boothe Luce |
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#15 |
ENGINE BUILDER
Join Date: Apr 2006
Location: Shortsville n.y.
Posts: 344
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Re: Truck Hesitates at 50mph - Coil?
How much pressure does the fuel pump make? Volume? It should pump a quart of fuel in maybe 30 seconds? FILTER? It sounds like the carb is running out of fuel.
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JIM ZAG |
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#16 |
Registered User
![]() Join Date: Aug 2006
Location: Woodstown, NJ
Posts: 669
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Re: Truck Hesitates at 50mph - Coil?
Check the base gasket on the carb. Also check for any other vacuum leaks.
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#17 |
Registered User
Join Date: Apr 2002
Location: Manitoba, Canada
Posts: 663
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Re: Truck Hesitates at 50mph - Coil?
Thanks for your help - fuel filter it was! I ruled it out too early because I thought I'd put one in recently. If I did, there was sure a lot of crap in the gas tank because the inside of the old filter was coated. The truck runs like a champion- three-on-the-tree rules!
__________________
Present: 2015 Tacoma. Yeah, not a GM, but I love it. 1969 GMC 32,000 - fix, drive, relax, fix... 2019 BMW R1250 GSA - Yahoooooooo 1979 Honda GL 1000 - retro touring at its best. Past: '05 Sierra 4x4 - Had 270,000 KM and running well when it was written-off by a stop sign runner. '94 F-150 from the "F word" company. I'll admit it...good truck. Sold what was left of it for $800 to a guy who came to pick it up at 11:00 PM with cash in hand. Hmm. '79 Sierra Grande (Black) organ donor - perfect rebuildable 4-bolt 350 and a good TH350. '76 Sierra Grande (Orange) - hate isn't too strong a word. Kid who bought it turned it into a hot rod. '68 C-10 R.I.P. - Dad's old truck...too far gone to resurrect. '59 C-50 - with hoist. Truck is gone, wife isn't. Nuff said. |
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