Random loss of power during cruise

[captainstevo25]

Hey guys, I'm a "newbie", but I've been on here for a few years. I still can't post in the tech forum...here's the deal. Sometimes during cruise, almost always in 5th gear around 70mph, the A/F ratio will go blank, and the car will lose power and start stuttering like crazy. I can usually make it go away by downshifting, but sometimes I have to do this a few times. I spent about an hour tonight searching, but haven't found anyone with the exact problem i'm describing. I found some similar issues, where there may have been potential ecu issues. Any ideas? Thanks

 

[dented_coffee]

Pull the ECU out and inspect it for any burnt traces on the top and bottom of the board and for any leaking caps or swollen processors. Also a boost leak test is something good to do.

 

[liljaywizzle85]

Do you get a check engine light when it happens? Do any lights illuminate on the dash when it happens?

 

[twicks69]

Likely a random misfire code. You can confirm by putting it in neutral when this happens, it will likely stall out, turn the car off, then back on and put back into gear. If it is then fine, check your cam angle sensor, your crank angle sensor, crank pulley for separation and your ECU.

Tim Zimmer via Evo Phone

 

[romeen]

Hey guys, I'm a "newbie", but I've been on here for a few years. I still can't post in the tech forum...here's the deal. Sometimes during cruise, almost always in 5th gear around 70mph, the A/F ratio will go blank, and the car will lose power and start stuttering like crazy. I can usually make it go away by downshifting, but sometimes I have to do this a few times. I spent about an hour tonight searching, but haven't found anyone with the exact problem i'm describing. I found some similar issues, where there may have been potential ecu issues. Any ideas? Thanks

It sounds like a fuel issue. Motor not getting enough fuel under sustained load. If your wideband is going blank when this happens then it could be leaning out beyond it's measurement range.

Start by changing the fuel filter to see if that resolves the issue.

 

[captainstevo25]

Thanks for all the replies.

I had a hunch that it might be ECU related, since it is always happening during cruise around 70 MPH.

As far as being a fuel issue -- does this make sense that it would only happen during cruise around 70? I would think it would be more prone to leaning out under load than during cruise, but I will admit I'm not too familiar with all that.

Thanks again for all the suggestions

 

[romeen]

Thanks for all the replies.

I had a hunch that it might be ECU related, since it is always happening during cruise around 70 MPH.

As far as being a fuel issue -- does this make sense that it would only happen during cruise around 70? I would think it would be more prone to leaning out under load than during cruise, but I will admit I'm not too familiar with all that.

Thanks again for all the suggestions

To be honest, I'm experiencing the EXACT same thing. Car accelerates fine. But when cruising at a steady speed, particularly in 5th gear, the car will start to shake and lose power. Downshift and give it more throttle and it goes away.

Every time it does this my wide band goes way lean. I put in a new fuel filter and it improved but did not completely resolve the problem. So I think my fuel pump is dying and I've got a new one on the way.

This is just a guess as to why it might do it during freeway cruising (I believe 5th gear cruising does put a fairly high load on the motor) and not during high load acceleration. It may have to do with the amount of voltage the fuel pump is getting. It may be limited during a 3000rpm cruise vs rapidly increasing rpms when accelerating. Again, this is pure speculation.

I guess I'll know after I install the new fuel pump. I suggested starting with the fuel filter only because it's a lot cheaper and easier to change. I'm hoping to get the new pump installed within the week. I'll let you know if it fixes the issue. Let me know if it does end up being the ECU.

 

[captainstevo25]

To be honest, I'm experiencing the EXACT same thing. Car accelerates fine. But when cruising at a steady speed, particularly in 5th gear, the car will start to shake and lose power. Downshift and give it more throttle and it goes away.

Every time it does this my wide band goes way lean. I put in a new fuel filter and it improved but did not completely resolve the problem. So I think my fuel pump is dying and I've got a new one on the way.

This is just a guess as to why it might do it during freeway cruising (I believe 5th gear cruising does put a fairly high load on the motor) and not during high load acceleration. It may have to do with the amount of voltage the fuel pump is getting. It may be limited during a 3000rpm cruise vs rapidly increasing rpms when accelerating. Again, this is pure speculation.

I guess I'll know after I install the new fuel pump. I suggested starting with the fuel filter only because it's a lot cheaper and easier to change. I'm hoping to get the new pump installed within the week. I'll let you know if it fixes the issue. Let me know if it does end up being the ECU.

Thank you sir. I actually replaced my fuel filter a a few years ago -- prob around 15K miles ago. I may go ahead and throw another one on there as well. Never thought about checking the fuel pump as well. Please let me know what you find out, and I'll do the same.

 

[Chazz1978]

Yeah. Im pretty sure when your wideband goes blank the car is running lean. Extemely lean. So depending on your mods or tune something needs to be changed. Needs more fuel. Ecu could be posible. But I would probably go over my fuel stuff.

 

[romeen]

Thank you sir. I actually replaced my fuel filter a a few years ago -- prob around 15K miles ago. I may go ahead and throw another one on there as well. Never thought about checking the fuel pump as well. Please let me know what you find out, and I'll do the same.

Well, I replaced my fuel pump with a brand new Walbro 255HP and the problem still exists. My wideband still goes extremely lean whenever it is doing this (17-19 AFR while trying to accelerate!). I had already planned to send my ECU out to be flashed even before this started happening so maybe that will reveal the problem.

I'll try to pull the ECU in the next few days to look for anything obvious but won't be able to send it out for flashing until the following week.

I'll keep this thread updated.

 

[captainstevo25]

Well, I replaced my fuel pump with a brand new Walbro 255HP and the problem still exists. My wideband still goes extremely lean whenever it is doing this (17-19 AFR while trying to accelerate!). I had already planned to send my ECU out to be flashed even before this started happening so maybe that will reveal the problem.

I'll try to pull the ECU in the next few days to look for anything obvious but won't be able to send it out for flashing until the following week.

I'll keep this thread updated.

Thanks man. I'm in the middle of prepping/painting, but as soon as I'm done with that I'm going to try and get this fixed.

I did have my friend come over who is a great mechanic, and he feels that it is probably not a fuel problem -- leaning towards ECU as well.