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Frequent Contributor

Anyone know Chevy 350s?

My girlfriend bought an old big body '91 Suburban with a 350 TBI. It had a 350 FI in it, but it was swapped out before she bought it. She was having trouble with it cutting out while driving and mentioned how it ran worse when it was humid or wet out. I thought right away that it just needed a tune up. I put plugs, wire, cap and rotor on it and it runs much smoother, but hasn't solved the problem. She says while driving around 55 it will sputter a little, the voltage is around 9, and the speedo will jump around when she has her foot on the pedal. When she lets off, the voltage goes back to 13ish and the speedo stops jumping. After running a little while it does the same at lower speeds. It sputtered and died on her today at around 45. She got it started and took it to the auto parts store and had the alternator and battery tested and they tested fine. After I did the tune up, I drove it and didn't notice anything. I figure it's something eletrical, but I'm not sure where to start. Anyone have any ideas?

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Veteran Advisor

Re: Anyone know Chevy 350s?

Check all the grounds, and the wires from the battery to the cab & ignition, including all connections and fusable links. 
When a ground connection starts going bad or a connection is loose, humid/wet conditions often make it worse.

The ignition system needs close to 12 volts, to produce a strong spark.  Anything that drops the voltage, will cause the spark to weaken, and that can lead to sputtering.  Since you said the dash reads only 9 volts, and the speedo jumps around, that tells me that you are losing power somewhere.  If memory serves me right, the speedo is electronic, and not the old cable-drive type.

Another thing to do , is the next time it is sputtering, look at the other guages, besides the speedo, and the volt meter.  Does the temperature guage suddenly show different than it normally runs?  Ditto the gas guage?

If all the guages act up, you then know it is either the main power/ground to the cab/dash, or possibly the ignition switch.

If only the speedo and voltmeter act up, it is likely a wire behind/under/in the dash.

 

I once had the alternator go out on my old Dodge pickup (1986 model, still with carb) and didn't know it for a couple days.  I didn't drive it in the dark, to need lights, (the volt meter hasn't worked for ages) and all I noticed is it cranked a little slow, and started sputtering at highway speeds, but it idled fine.  Finally, one day I came home at dusk, and when I'd turn the lights on, the engine cut out.  Turn off the lights, and it ran fine.  Limped it the last 2 miles or so home, just running the 4-ways (thank goodness I could still see) and replaced the alternator & cleaned up the battery connections, and all was well again.

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Frequent Contributor

Re: Anyone know Chevy 350s?

I'll ask her about the other gauges. She lives about 1.5hr away so I can't just run over and see. I think she did say something about it not using that much gas (which would suprise the heck out of me with that big boat!), so I wonder if the gas gauge is not working. She did just have the steering column worked on because it was loose and flopping around. I wonder if something got fubared in there. I don't recall it doing this before then come to think of it. The truck did sit in my driveway for several weeks while my brother put the differential back together because a bolt worked its way out and made a mess. To me, it seems like it started after then, but I can't say for sure.

 

I have an old '90 Ford with the 7.3L IDI that the alternator was dead on and I didn't know it. I just was using it as an around the farm truck while slowly fixing it up for a daily driver. It would drain the batteries dead (turned out that was the regulator), but otherwise would run just fine.

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Frequent Contributor

Re: Anyone know Chevy 350s?

I also forgot to mention that her radio (aftermarket) will randomly turn on and off. She says at only higher speeds, but sometimes when going slower. All other guages are working normally according to her. She did say the oil pressure guage is reading around 60 which sounds kind of high to me. It was doing that since she bought it though. She says it only really started doing all this within the last couple days, but I recall the radio acting up for at least a couple weeks.

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Frequent Contributor

Re: Anyone know Chevy 350s?

One last thing, she said the brights are pretty dim also. I don't know if it's related or not though.

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Veteran Advisor

Re: Anyone know Chevy 350s?

GM products with tilt wheels were notorious for having wiring problems where it would hinge in the steering column.  If I couldn't find anything obvious under the hood, I'd start there, if it has tilt.

 

Your Ford was a diesel, so it didn't need spark to run.  As long as the battery would turn it over fast enough to start, it would likely run fine all day.

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Veteran Contributor

Re: Anyone know Chevy 350s?

7.3 diesel does need elec to run to keep the fuel solenoid turn on

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Senior Contributor

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Veteran Advisor

Re: Anyone know Chevy 350s?

True enough, but it won't 'sputter'.  It will either run, or it won't.

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Frequent Contributor

Re: Anyone know Chevy 350s?

Thanks for all the help, guys. I really appreciate it. Shop rates are pretty crazy especially with eletrical, so as long as it's not in the steering column I hope I can fix it and save her some money.

 

My brother told me that the 7.3L has some kind of solenoid of something electrical in the injection pump or something or other that wouldn't work if the electrical system wasn't working. I'm no diesel mechanic (he's going to school for it), so I didn't know. I blew the transmission this year hauling hay, anyway. That wasn't a fun day.

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