AMC Eagle Den Forum
The Mighty 258 => The Engine => Topic started by: 85AmCfreak on July 08, 2012, 08:25:09 PM
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I was on the highway in Jersey and noticed the sx4 bogging above 80 mph. This is very confusing considering the car is fine from 0-60 mph. But its not noticeable until you hit 75-80mph then the car starts to slow down and bog like its gonna stall, Until around 65 mph. Then I can get the car going again but once it happens it will continue, until I drop below 65. Does anyone know whats going on here??
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Sounds like your running out of fuel. I believe I would take a fuel pressure reading from the pump.Maybe replace the fuel filter or look for a restriction in the fuel lines. Have you had the carb rebuilt? Its possible the float is set to low.There is also a fuel filter in the tank. When I replaced my fuel tank I found my filter in the tank was packed solid with crap.I cleaned it with berrymans b-12 chemtool before I reinstalled it.I had a corvette once that had the very same problem your talking about. After many weeks of work and countless dollars I found the fuel return line to the tank was to large.Put a reducer in the return line and problem went away. Hope this helps and good luck.
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make sure that the fuel sock isn't blocking the flow. They tend to collapse after a few decades of MTBE abuse.
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The problem has been there for a while. No restriction in the fuel lines Just pulled the tank and cleaned it out . New line front to back and sending unit looked newer. I have no return lines single inlet single outlet fuel filters. I am running a weber 38 carb setup from weberdirect for the 258. I just don't get it. :-\ there should be no problem
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What RPMs are you running at that speed, or what axle ratio do you have?
You may be hitting the top end of the motor if you have 3.08s.
I have the 2.35s and it will peg the 85mph speedo at 2700rpms, and I can keep pulling over 3000 probably putting it close to 100mph :o.
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I have 2.35's also, no way am I topping that motor out. You could probably do 120 mph in that car. So any other ideas? I can't seem to figure this out.
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I have 2.35's also, no way am I topping that motor out. You could probably do 120 mph in that car. So any other ideas? I can't seem to figure this out.
Yeah, there goes my idea, and yeah I calculated and with 2.35s with stock tires at 4000 rpms in Drive, the car will be rolling close to 140mph :o.
Sounds like you're not getting enough air or fuel to the motor though somehow.
Can you give more symptoms/details to this "bogging" condition?
Does it stumble/sputter, or just lug like you're under a large load?
Could be something in the transmission/transfer case/axles causing an excess load to the motor at a certain speed.
Like a bearing taking a load or torque converter or viscous coupling.
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You may be hitting the top end of the motor if you have 3.08s.
i have the 3.08s in Eagle Eyes and i have had her up to 120 with them and i was still gaining speed when i let off the throttle.
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...Sounds like you're not getting enough air or fuel to the motor though somehow....
I agree. If you've eliminated a fueling problem, suggest you ensure it is getting enough air. Once you cover the fuel and air, check your ignition to ensure it is keeping up under load.
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Something in the fuel line jamming the pump inlet valve open? I take the "sock" off the fuel line in the tank because they turn mushy from the MTBE that CA and Shell rammed down our (carb) throats. It collapses at speed and blocks off the fuel inlet in the tank. (3 Jeeps, 2 Eagles and various other brands of car had the same problem)
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Sounds like you're not getting enough air or fuel to the motor though somehow.
Can you give more symptoms/details to this "bogging" condition?
Does it stumble/sputter, or just lug like you're under a large load?
Could be something in the transmission/transfer case/axles causing an excess load to the motor at a certain speed.
Like a bearing taking a load or torque converter or viscous coupling.
I don't really know how else to explain it (wish you guys were here to see what I am talking about) It only happens when I am on the highway. Its like everything is fine up until 65-70 then if I mash the accelerator she will get right up to 80 and then start to lose power. It will stay like that until I let her drop down to around 60-65 then I can hit it again back up to 80 then it starts all over. Bogging down even if I try again around 70 it will now need to drop down to 55-60 to get any power back.
I guess I could pull the sock off the sender but..... :'( I just put all that back together,
If I loose the sock on the tank what can I replace it with? Do you even need a sock?
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Ya know I have thought about this and thought it and I know I said it before but I believe its worth saying again. I think you are running out of fuel.I believe I would have a look at the float level in the carb.If its set to low at higher rpm the engine is starving for fuel and then when you back off its allowing it to catch up and then refilling the fuel bowl.Could be a several other issues but believe I would have a serious look at the carb first.
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I put an in-line filter before the pump when I removed the sock. (see through so I could see if any junk got in there)
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Ya know I have thought about this and thought it and I know I said it before but I believe its worth saying again. I think you are running out of fuel.I believe I would have a look at the float level in the carb.If its set to low at higher rpm the engine is starving for fuel and then when you back off its allowing it to catch up and then refilling the fuel bowl.Could be a several other issues but believe I would have a serious look at the carb first.
I changed the carb out. Back to the 32/36 took it out on the high way and its still doing the same thing
I put an in-line filter before the pump when I removed the sock. (see through so I could see if any junk got in there)
So if there is no sock it will still pickup fuel? I do not have to make any other modifications to the sending unit?
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Well than,shut my mouth! Anyway still thinkin but can't help thinking its fuel related.
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Well eagleman it could still be the sock in the tank collapsing....
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The sock is just a screen in the tank. On FSJs (full size Jeeps) I also add a short piece of hose so the bottom few gallons in the tank aren't always left behind.
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regular fuel line with a clamp?
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Yup. The filter is in the line now. You can still get socks from places like http://bjsoffroad.com (for full size Jeep but it looks identical) but I figure why bother if my tank is clean?
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Thanks for the info I will get back to you guys as soon as I get the job done..
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OK so I finally got around to removing the fuel sock. Unfortunately it didn't solve the problem, sorry carnuck. I Got on the highway to spend the weekend up in Pennsylvania and realized I couldn't get over 50 mph (Not good) I went about 15 miles and was about to turn back. Then I remembered I had installed an electric fuel pump but I never wired it. So on the shoulder of 280 west bound I started wiring. Lets just say I was doing a 100 mph before I knew it, minus bog (gotta love that GPS speedometer) I have to give credit to eagleman cause he was the first to say it. I seem to have a fuel problem, but I don't know where. Is it possible the fuel pump is not giving enough pressure at high rpm? Its a new acdelco pump just installed 3 months ago and the old one was doing the same thing. Maybe the lobe on the cam for the fuel pump is bad? Any suggestions would be great.....
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Maybe the lobe on the cam for the fuel pump is bad? Any suggestions would be great.....
SB Chevys used to have this problem...I've never heard of it in a 258 :eagle:
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Would the electric fuel pump act as a choke point in the system when it wasn't wired and operational???
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Would the electric fuel pump act as a choke point in the system when it wasn't wired and operational???
I wondering the same thing.
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OK so I finally got around to removing the fuel sock. Unfortunately it didn't solve the problem, sorry carnuck. I Got on the highway to spend the weekend up in Pennsylvania and realized I couldn't get over 50 mph (Not good) I went about 15 miles and was about to turn back. Then I remembered I had installed an electric fuel pump but I never wired it. So on the shoulder of 280 west bound I started wiring. Lets just say I was doing a 100 mph before I knew it, minus bog (gotta love that GPS speedometer) I have to give credit to eagleman cause he was the first to say it. I seem to have a fuel problem, but I don't know where. Is it possible the fuel pump is not giving enough pressure at high rpm? Its a new acdelco pump just installed 3 months ago and the old one was doing the same thing. Maybe the lobe on the cam for the fuel pump is bad? Any suggestions would be great.....
If the electric pump was inline at the time you put the sock in, it could slow the fuel flow down. Crud from the tank could also be jammed in the inlet valve of the fuel pump (maybe warranty the pump after testing it with the electric pump bypassed)
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Would the electric fuel pump act as a choke point in the system when it wasn't wired and operational???
It was happening before the electric fuel pump was installed.
If the electric pump was inline at the time you put the sock in, it could slow the fuel flow down. Crud from the tank could also be jammed in the inlet valve of the fuel pump (maybe warranty the pump after testing it with the electric pump bypassed)
I doubt it but it is a possibility I will not be available to really work on the car till next week. I will have to check it out then.