1968 Chevy K10 SWB Overlander

[1stDeuce]

Question for those that know:

Is it possible for a engine to dog/sputter due to an air filter that's too small? I had to get a new air filter since installing the brake booster. Now, when it gets hot, the engine dogs and lags. It sputters a bit, too, especially when not moving. When it's colder outside, the truck doesn't dog as much. I'm wondering if my new air cleaner is just too small...

If it's not the air filter, I'm thinking I might have some gunk in the fuel lines. Any thoughts?

Check the fuel pressure. I don't remember if you're using an in-tank pump, or an in-line pump, but we went through several in-line pumps on my brother's fuel injected Scrambler... Don't know why, but they didn't live long. It would end up having vapor lock symptoms, and you'd purge the fuel rail and it would run ok again for a while... In the hot of course... Once the temps dropped, it would run correctly. Grrrr.

You may also have a sensor dying or dead so that when you hit open loop, it's running poorly. As stated above, O2 could do that, but so could the MAP sensor. If it runs well cold, then the TPS is probably working right, since it bases open loop on TPS mostly, with input from the MAP. Hmm, I guess that points to the O2 sensor, doesn't it...

A HUGE vacuum leak might do the same, but should make it run like poo all the time, not just when it's warm...
Chris

 

[snekvasil]

Check the fuel pressure. I don't remember if you're using an in-tank pump, or an in-line pump, but we went through several in-line pumps on my brother's fuel injected Scrambler... Don't know why, but they didn't live long. It would end up having vapor lock symptoms, and you'd purge the fuel rail and it would run ok again for a while... In the hot of course... Once the temps dropped, it would run correctly. Grrrr.

You may also have a sensor dying or dead so that when you hit open loop, it's running poorly. As stated above, O2 could do that, but so could the MAP sensor. If it runs well cold, then the TPS is probably working right, since it bases open loop on TPS mostly, with input from the MAP. Hmm, I guess that points to the O2 sensor, doesn't it...

A HUGE vacuum leak might do the same, but should make it run like poo all the time, not just when it's warm...
Chris

My weekend project :bike_rider: Thanks for the help!

 

[huntsonora]

this build is so cool on so many levels

 

[SlowJoe]

The ethanol fuel we are now forced to run is hygroscopic. When it gets enough water content it will form a sludge that will roll around the bottom of the tank and when it accumulates enough, it can be sucked up the intake port in the tank by the pump and will cause intermittent running problems like you describe. These problems are more prevalent with vehicles that sit often for extended periods. It is best to run a can of fuel treatment through the tank every so often. I tend to do it every oil change, and if your vehicle sits a fair amount, I would do it every 4-6 months. Any fuel treatment that removes water will be fine, but I tend to use seafoam or STP fuel treatment. The key is it needs to say "removes water" pretty prominently on the label and is not just touting it's cleaning abilities. It is best if you are able to run the tank down low, add the treatment and then drive to fill the tank. This allow the treatment to combine with the sludge and agitate the mixture into suspension before adding the fuel so it can be flushed out. It is also best to do this procedure right before topping off the tank on a long trip that so that the agitated mixture will be burned and it can not get the chance to settle back to the bottom of the tank. Good luck with your problem!

 

[snekvasil]

The ethanol fuel we are now forced to run is hygroscopic. When it gets enough water content it will form a sludge that will roll around the bottom of the tank and when it accumulates enough, it can be sucked up the intake port in the tank by the pump and will cause intermittent running problems like you describe. These problems are more prevalent with vehicles that sit often for extended periods. It is best to run a can of fuel treatment through the tank every so often. I tend to do it every oil change, and if your vehicle sits a fair amount, I would do it every 4-6 months. Any fuel treatment that removes water will be fine, but I tend to use seafoam or STP fuel treatment. The key is it needs to say "removes water" pretty prominently on the label and is not just touting it's cleaning abilities. It is best if you are able to run the tank down low, add the treatment and then drive to fill the tank. This allow the treatment to combine with the sludge and agitate the mixture into suspension before adding the fuel so it can be flushed out. It is also best to do this procedure right before topping off the tank on a long trip that so that the agitated mixture will be burned and it can not get the chance to settle back to the bottom of the tank. Good luck with your problem!

I actually only run non-ethanol gas in my truck due to the issues you just mentioned. I'll keep your advice in mind, though! Thanks.

 

[snekvasil]

this build is so cool on so many levels

Thanks for the kind words!

 

[SlowJoe]

I actually only run non-ethanol gas in my truck due to the issues you just mentioned. I'll keep your advice in mind, though! Thanks.

Well you dont have to worry about the ethanol sludge issues then! It is still worth checking to make sure you do not have water in your fuel from another source, or that has just accumulated over time. If that is not the case I would check the fuel pump and filter if you havent already. I would also be suspicious of a float that is sticking and either dumping or starving it for fuel. Too much fuel could make it spit and stumble just like starving it would, but you would likely smell it running rich if that were the case. Good luck and nice truck!

 

[1stDeuce]

@SlowJoe: It's fuel injected.

But that's a good point... Not that I think it's the issue, but running ONLY non-oxygenated fuel can allow some water to build up in the tank... a little 10% every now and then keeps it clear of accumulated water at least...

 

[SlowJoe]

@SlowJoe: It's fuel injected.

But that's a good point... Not that I think it's the issue, but running ONLY non-oxygenated fuel can allow some water to build up in the tank... a little 10% every now and then keeps it clear of accumulated water at least...

Now I am really confused... I could have sworn I read his write up and it said it had the original inline 6 in it? Is there some engine swap I missed somehow? I was wondering what someone was talking about O2 sensors for... I figured they were talking about some other truck...

 

[locrwln]

Original motor with Howell 4.3 TBI FI injection system.

Jack

 

[snekvasil]

O2 sensor

And the winner goes to...O2 sensor!

Running like a charm now. Now hiccups or glitches or stutters at all. I went for a long drive and it was as smooth as ever. Thanks so much for all of you that helped! It would've taken me a while to pinpoint the problem without your help.

 

[driller]

Nice

 

[NevadaLover]

Are you using a stock GM 1 wire O2 sensor or an upgraded 3 wire sensor?? If it's a 1 wire you should upgrade to a 3 wire, it makes a big difference by heating the sensor internally and that helps the sensor start working sooner and keeps it working when doing low speed or idle time, it will also help the sensor live longer!

 

[snekvasil]

Are you using a stock GM 1 wire O2 sensor or an upgraded 3 wire sensor?? If it's a 1 wire you should upgrade to a 3 wire, it makes a big difference by heating the sensor internally and that helps the sensor start working sooner and keeps it working when doing low speed or idle time, it will also help the sensor live longer!

Thanks for the tip!

 

[Bojak]

2nd the 3 wire sensor. Finally got mine done and it has cured what has been a 2 year fight with some issues I have been battling. Wish I would have done it 2 years ago.