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Topic: Fuel or electrical problem????

in Forum: C3 Fuel, Emission Control, and Exhaust Systems

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Fuel or electrical problem???? (1/8)
9/30/14 8:41pm

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

Since I put in a new engine 427 with a rochester 750 cfm carb everything seemed to work fine, no more vapor lock and good acceleration.

With 900 miles on the engine I now have a problem, whereas it may be an electrical issue or fuel.

Problem---Steady speed of 70 or less at times the engine cuts out, like turning the ignition off and turning it back on again. On a 68 the seat belt warning light on the dash has a light and a button that warns you to put the seat belt on. You press the button to turn the light off. The seat belt light will come on each time the engine cuts out and I have to push the button to turn the light off. The light comes back on the next time the engine cuts out. However the instruments gauges fuel, oil, temp etc will continue the same reading and not fall off as the seat belt light, or as when you shut the ignition switch off, and all the gauges drop.

I can go hard on the pedal and it will not cut out, but just steady speeds it want to cut out or miss. It may go for a few miles, and it starts again. Just wondering if the coil is the problem. The plugs and wires are all new and intact.

NO water in the gas, and I am using non methanol gas.

I have put new wire harnesses in the dash as well as the engine compartment.

The fuel pump is new, but could it not be staying up with the carb?? The fuel filter is also new. I can understand it more if you went hard on the gas and it cut out rather than a steady speed.

Any help would be much appreciated.

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Re: Fuel or electrical problem???? (2/8)
10/1/14 12:40pm

F4Gary

Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 1409

Sounds like your ignition switch is cutting out and when it comes back on, it's like when you first get in the car and switch it on (causing the seat belt light to come on).

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Re: Fuel or electrical problem???? (3/8)
10/1/14 12:57pm

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20129

That'd be my first guess, too. Definitely not fuel or a coil problem. What harness did you replace under the dash?
I would start looking at the harmonica connector on the steering column, and make sure it is nice and snuggly connected, then move on the to fuse box. If you replaced the harness on the engine side, then you had to take the firewall connection loose that connects the engine harness to the fuse box. That one dang connector can cause all sorts of strange electrical problems if it is not completely seated, and sealed. As far as the gauges not cutting out when this happens, it's prolly happening so fast the gauges just don't have time to respond, since they have "buffers" on them to keep the needles from bouncing.
Anywho...I'd sure be looking at the new harness connectors... Thumbs Up

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Joel Adams
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Re: Fuel or electrical problem???? (4/8)
10/1/14 11:17pm

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

I have new fuse boxes on both the dash harness and engine harness. I replaced both, and I did at first have some problems in not getting a good connection between the outside fuse box connection to the inside. It has one bolt in the center that holds the two parts together.

I did not replace the dash ignition switch because the aftermarket one is not correct and does not match up. The ignition switch harness has three legs that connect to the ignition switch behind the dash. The new aftermarket switch for the 68 does not match up with the connector legs of the harness. I contacted the people who make the switch and others who vendor it. I don't know if this has been corrected, but I have pictures and proof that their product does not work for the 1968 corvette ignition switch, without major modification.

Could it be the modual that is in the distributor in place of the points. Had a problem once with this and i though it was the spark plug wires or plugs, because the engine was missing bad, Thus I replaced them, and it continued until I discovered it was the modual in the distributor.

I replace the entire dash pad and all instruments, but did have the problem with the ignition connection not being correct from the vendors, and I did have problems getting the plastic legs of the connection to hold with the original switch, however it their was a problem here, you think it might happen most of the time rather than just cruising??????

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Re: Fuel or electrical problem???? (5/8)
10/2/14 1:22pm

Adams' Apple

Oh SNAP! I forgot about the '68 having the iggy switch in the dash! DOH! Wacko

Be that as it may...I can't see a problem with the ignition module causing the seatbelt light to come on at the same time the engine stumbles....that still appears to be a problem with the ignition switch/wiring somewhere. Ghosts in the electrical system can cause all kinds of goofy problems that make absolutely no sense.

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Re: Fuel or electrical problem???? (6/8)
11/26/14 12:00am

rlu1968
Former Member
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Gordonvillle, TX - USA

Vette(s):
1968 Roadster 427

Joined: 11/28/2003
Posts: 228

Replaced the ignition switch.

However the problem was in the green wheel shut off on the battery. I have a cut off switch connected to the battery positive side in which you turn the green wheel on top of the positive battery side switch one way to cut off all power to the car and turn it the other way to get power. This is just a way of preventing any problems in the electrical area when the car is parked.

Well this had worn out and was not getting a good contact anymore. So any bouncy movement of he car would cause it to short out and cut the power to the engine. Thus going on and off at different times.

Just a FYI for anyone who may have a similar problem.

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Re: Fuel or electrical problem???? (7/8)
11/26/14 1:21pm

Adams' Apple

Well crap! Never thought of that, either! Glad you found it! Thumbs Up

Sad thing is, I've actually HAD that problem before on mine! The contacts corrode just enough from the battery acid fumes to cause this. Mine did it to me once when I had the '74 on display at the Texas State Fair. Time to leave, car wouldn't start. Took a few minutes to figure it out, but when I finally got home, I took that thing off and cleaned it really well, then sprayed it with ZEP 45. Haven't had a bit of trouble with it since.

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Re: Fuel or electrical problem???? (8/8)
11/26/14 3:25pm

F4Gary

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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 1409

I'm surprised he didn't get a big bang from the raw fuel in his exhaust system when the ignition cut off and then back on.

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