surging at crusing or in third gear

[87454westernhauler]

I have an 80 c10 350/th350 SBC. It runs fairly well in at low speeds, but when I get into third gear and step on it any it starts to surge and then I have to back off. any ideas as to a quick solution, going to start driving it as a daily driver after my 18th birthday in may. I am wondering if it is possibly a weak fuel pump??

[Irish_Alley]

do you have a egr

[78 Chevyrado]

check the fuel filter first or change it if its been a while, then check the pump.

[87454westernhauler]

I changed the filter about a month ago, I may do that again, I is whatever the stock ignition system would be for an 80 350. I did just replace the cap rotor and coil. do you think that it could be that the module is weak???

[78 Chevyrado]

The modules solid state.  They won't get weak, It will either work or it won't.  They can work intermittently though.

If its the filter, you could have gotten a crappy tanks of gas, or filled up right after the gas-truck left or something.  If you still have the stock carb, you know how super TINY the filters are and it doesn't take much to clog them up.

Usually if it's an ignition problem, it'll run bad at all rpms.  What you desribe sounds like a fuel starvation problem...  It runs fine at low rpms because the restriction lets enough through at low rpm, but at high rpm when the engine needs more fuel, it wont let enough fuel through.

[87454westernhauler]

I can usually floor it when it is in 1 and 2 with not to much stuttering or surging but it does do it in first and second if I'm driving it hard for more than a few seconds, I'm going to try another filter again and see if it works better

[VileZambonie]

The modules solid state.  They won't get weak, It will either work or it won't.  They can work intermittently though

Actually they can get weak. In fact when you compare oem to aftermarket modules on an oscilloscope (especially Napa parts for some reason) and new vs old you will notice quite a difference in amperage when performing a current ramp test. With age the amperage can often fade and many ignition modules are designed to be current limiting as well.

In this example you can see a normal current ramp as the module is working



In the next example you can see the coil is firing multiple times most likely causing detonation. This is either caused by a faulty icm input or the icm breaking down.



I have some screen shots somewhere of a comparisson between two identical modules if I get some time I'll dig. Nevertheless, your most likely cause ignition secondary so check the plugs and wires next.

[87454westernhauler]

I just replaced the pugs and wires.

[VileZambonie]

Did you properly gap all of the spark plugs? None of the insulators or electrodes are cracked? The wires have good integrity? Try to wet test the ignition system with a spray bottle filled with water and see if it worsens?

[klaussk]

I know in Holley's there is a power valve that feed more fuel to an engine during quick accelerations under heavy load conditions. I'm sure the stock Q-jet has to have a similar piece. If one were to go bad it could cause fuel starvation at a higher speed acceleration. I could be totally wrong though

[87454westernhauler]

well, I took it out saturday and drove it about 20 miles to go get a free set of BFGoodrich comercial tires and a nice set of crome exaust tips as an early graqduation gift . not perfect tires, but over 75% left on them and no dry rot. I drove it about 60-70mph, surged a little when I steped down on it at 60, but not bad. Took it into town today to get them mounted, it was surging when ever I steped down on it as usual again. Relized now that the front left caliper is sticking after I finnaly got a desent set of tires on it, so I need to get a new set of pads and calipers. The tires were scary  , dry rotted worse than I thought . My dad rode with me after puting tires on it and it sounds like a pluged filter to him. wound up driving over 60 miles in it this weekend.  Im going to the parts store hopefuly tomorrow and am going to get a couple of extra filters and going to see how much pads and calipers are going to set me back.

[1979C20]

I know front pads were like 20 or 30 because I have a 3/4 that needs the heavy duty pads. And the rear shoes are like 24. Im not sure about calipers or drums though, mine are still in good shape.

[87454westernhauler]

Rotors are about 30 a piece, and a caliper set is 30 with cores, and pads are about 25. I may just steel a caliper off of my dads 87 1/2 ton and wait till my next pay check and just replace all of the parts at once.

[topp]

When I started driving my '87 on a regular basis, I was replacing the filter about once a week for 2-3 months.  when the fuel that came out of the filter was not "dirty" is when I scaled back on replacing the filter so often....

[bake74]

     x2 on what topp said.  The filter may seem ok and flow ok, but when a filter starts to get plugged, it will allow fuel to flow through and progressivly get slower and slower, sometimes it just slows down and still allows fuel to flow through, but not enough, making you think all kinds of wierd stuff is going on.