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Discussion Starter · #1 ·
Yesterday, I just drove several hundred mile trip. Most of it I was driving about 60-62 mph. The trip was all in Florida, so relatively flat. Most of the time I had 15-17 psi boost and 1000 EGT. So after driving five hours or so, I happened to look at my gauges and saw I was going 53 mph. The limit was 55 and the traffic was 60, so I was kind of holding up traffic.

I went to push on the pedal and found I was on the floor. The boost was at about 22-24 and my EGT was at 1100-1200. I wasn’t on a hill or anything. The water temp was around 210. It wasn’t running bad except it wasn’t excellerating with my foot on the floor. I held this situation for probably 10 minutes.

I wasn’t sure what I wanted to do about this when I missed my turn. When I stopped to turn around, the thanksgiving traffic kept me at idle for a few minutes. In that time, the E-fans brought the water temp down to about 160. I got back out on the road and the truck seemed to run fine.

Today I took it for a drive and it seemed to be fine also. What gives? Normally, This truck will do over 70 mph if I floor it. I looked at the exhaust when it was acting weird and there was no smoke.

Any ideas?
 

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What was your engine RPM during those incidents? 15-17 PSI boost and 1000 deg EGT seems a little high for just cruising on mostly level ground at 60 MPH. Sort of expect 8-10 PSI and 600-800 deg EGT in that situation. Of course I keep forgetting you're running an army style cement block. Could you possibly have an issue with the AFC unit. That is supposed to advance fuel as boost increases.
 

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Discussion Starter · #5 ·
Today I found one of my E-fans is running intermittently. If it were to be off and I was only running one fan, I could see higher water and EGT temps. I still don’t follow the high boost and low speed.
 

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Boost is based more on load than speed. To cruise along on the highway with minimal load you don't need that much power once you're up to speed. Now, come to an incline or hill requiring more power the boost will rise. Your vehicle is creating a heavier load on the engine. Large tires and poor aerodynamics create more load. Just the nature of the beast,
 

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Discussion Starter · #7 ·
Boost is based more on load than speed. To cruise along on the highway with minimal load you don't need that much power once you're up to speed. Now, come to an incline or hill requiring more power the boost will rise. Your vehicle is creating a heavier load on the engine. Large tires and poor aerodynamics create more load. Just the nature of the beast,
I understand all that, but something changed for a bit. I was at 50 mph and pedal on the floor for more than five minutes. This is Florida. There are no hills that long.
 

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What boost numbers were you seeing before this happened ? Modest boost leak could cause this or a glitch with the AFC system, I recently had a AFC issue where the fuel pin follower was wearing on the aftermarket fuel pin the pin was softer than the Bosch pins and the interface between the two was rough.
Could your KSB be malfunctioning and changing your timing?
Maybe a transmission issue... was your tach giving normal data?
You had one fan out and with the after cooler high coolant temps equal higher charge air temps so we know there was some change there but could it account for what you encountered i don't know, you could try MatchBot and play with intake temps to see if it changes things enough that it could be the cause.
I'm just thinking out loud here I just had issues with my rig but it was early AM of the first morning in the low teens so it was lack of winter diesel in the tank.
 

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Discussion Starter · #9 ·
What boost numbers were you seeing before this happened ? Modest boost leak could cause this or a glitch with the AFC system, I recently had a AFC issue where the fuel pin follower was wearing on the aftermarket fuel pin the pin was softer than the Bosch pins and the interface between the two was rough.
Could your KSB be malfunctioning and changing your timing?
Maybe a transmission issue... was your tach giving normal data?
You had one fan out and with the after cooler high coolant temps equal higher charge air temps so we know there was some change there but could it account for what you encountered i don't know, you could try MatchBot and play with intake temps to see if it changes things enough that it could be the cause.
I'm just thinking out loud here I just had issues with my rig but it was early AM of the first morning in the low teens so it was lack of winter diesel in the tank.
I had been driving all day, but not on interstates. So it was up and down on speeds. When I was in between towns the boost was 15-17 at 60 mph. I wasnt really paying attention when it started, but after I realized I was on the floor, I Couldn’t believe I wasn’t excellerating.

Tomorrow I have to drive home. I’ll see what happens. I hope it’s not AFC issues. I really don’t understand that stuff enough to fix it. I hate to pay someone.
 

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I had been driving all day, but not on interstates. So it was up and down on speeds. When I was in between towns the boost was 15-17 at 60 mph. I wasnt really paying attention when it started, but after I realized I was on the floor, I Couldn’t believe I wasn’t excellerating.

Tomorrow I have to drive home. I’ll see what happens. I hope it’s not AFC issues. I really don’t understand that stuff enough to fix it. I hate to pay someone.
On the drive home pay attention to EVERYTHING from when it's getting up to temp, at what temp does the KSB shut off, boost #'s, EGT's, what comes out of the tail pipe. Then what changes and when/why it changed, try different throttle settings under different loads........ With a little luck you might detect some sort of pattern that might point you to a cause. I'd guess that it's something small/simple that changed, moved or loosened or the like what with how it started.
Good luck on the trip home I've been in your shoes and the fix is there just need more data/time to find it.
 

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Sounds like an issue like me fathers 93 gen one had, turns out his air filter was clogged or collapsed and was blocking air flow. I don't quite understand why it drove his EGT's up, other than asking the motor to work with more fuel and less air, which we know unbalanced fuel/air mixture can cause issues like an increase in temps.
 

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Discussion Starter · #12 ·
Sounds like an issue like me fathers 93 gen one had, turns out his air filter was clogged or collapsed and was blocking air flow. I don't quite understand why it drove his EGT's up, other than asking the motor to work with more fuel and less air, which we know unbalanced fuel/air mixture can cause issues like an increase in temps.
Interesting. I live on a dirt road. I have to clean my cars air filter all the time. The truck has a big filter that shouldn’t get clogged as easy. But I’m going to check it.

On the trip home, it started running like total sh*t. Wouldn’t go over 40 mph and stalled a couple times. My fuel gauge was giving me trouble, so I decided to put some fuel in her. (The tank was not empty) With in about 5 miles it started running much better. It was not fixed, but at least it would go 50-52 mph.

So I’m driving along at 52. The pedal is not on the floor. So I push it a little more and nothing happens. Doesn’t make any more noise. Doesn’t raise the EGT. Doesn’t raise the boost. Of course it doesn’t go any faster. So I back off to the same spot and keep cruising. After a minute, the truck suddenly excellerated . I had to back off because I was coming in to a speed zone. I though maybe it was fixed, but later on it was back to the 50-52 stuff.

Right now, I’m leaning to the fuel filter. It definitely got better after filling the tank. Maybe the pump is having trouble sucking through the inline filter. The extra fuel could have helped by pushing from the back side.

Now that I’m home, I can do some more testing.
 

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Interesting. I live on a dirt road. I have to clean my cars air filter all the time. The truck has a big filter that shouldn’t get clogged as easy. But I’m going to check it.

On the trip home, it started running like total sh*t. Wouldn’t go over 40 mph and stalled a couple times. My fuel gauge was giving me trouble, so I decided to put some fuel in her. (The tank was not empty) With in about 5 miles it started running much better. It was not fixed, but at least it would go 50-52 mph.

So I’m driving along at 52. The pedal is not on the floor. So I push it a little more and nothing happens. Doesn’t make any more noise. Doesn’t raise the EGT. Doesn’t raise the boost. Of course it doesn’t go any faster. So I back off to the same spot and keep cruising. After a minute, the truck suddenly excellerated . I had to back off because I was coming in to a speed zone. I though maybe it was fixed, but later on it was back to the 50-52 stuff.

Right now, I’m leaning to the fuel filter. It definitely got better after filling the tank. Maybe the pump is having trouble sucking through the inline filter. The extra fuel could have helped by pushing from the back side.

Now that I’m home, I can do some more testing.
My gut says AFC, I'd pull the AFC cover remove the fuel pin and inspect it look at the tapper where the follower rides to see if its wearing as well as the OD of the pin below the tapper for foreign matter that could cause it to stick IIRC i used a .45 cal bore brush to clean the fuel pins bore.
I have a core VE on the bench now so If pics of the process will help let me know and I'll walk you through it step by step.
 

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Discussion Starter · #14 ·
My gut says AFC, I'd pull the AFC cover remove the fuel pin and inspect it look at the tapper where the follower rides to see if its wearing as well as the OD of the pin below the tapper for foreign matter that could cause it to stick IIRC i used a .45 cal bore brush to clean the fuel pins bore.
I have a core VE on the bench now so If pics of the process will help let me know and I'll walk you through it step by step.
Yea, I’m rusty on that stuff. I did some work in there. I can’t remember what exactly. I think I turned it as per some utube. I do have a .45 brush. Are you saying if it sticks there will be a dead spot where increasing the throttle will do nothing? Below that spot, it seems to work fine.

Also, I need to remote mount my fuel pressure gauge. It is mounted solid to the engine and it vibrates so much its hard to read.
 

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Like Steve says, it sounds like an AFC issue. Could you have a broken line from the intake to that unit? It's like there is not increase in boost because there's no increase in fuel. Sure doesn't hurt to check fuel filter too. Could a weak lift pump also be a culprit?
 

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Yea, I’m rusty on that stuff. I did some work in there. I can’t remember what exactly. I think I turned it as per some utube. I do have a .45 brush. Are you saying if it sticks there will be a dead spot where increasing the throttle will do nothing? Below that spot, it seems to work fine.

Also, I need to remote mount my fuel pressure gauge. It is mounted solid to the engine and it vibrates so much its hard to read.
When I dealt with this it was acting like a high strung 2 stroke dirt bike in that it would be lazy accelerating then stall totally and right after that it would fuel normally,
but should I let it drop back to lower boost and reaccelerate it would do the same thing.
I found some debris of some sort at the base of the fuel pin so cleaned pin and bore and it has been better but I reinstalled the Bosch fuel pin that I modified with a more aggressive tapper using the heavier spring from the aftermarket pin and so far so good.
 

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Discussion Starter · #17 ·
One other thing I will mention, I got the best fuel mileage on this trip. Lol. I got 15.4 mpg when I usually get about 13.8. I guess it was cause I was driving so long at 50 mph.
 

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Don’t know if this helps but I read that a person is supposed to spray some lubricant in the AFC rubber vent tube annually to keep corrosion down and lubricate the AFC assembly. AFAIK there is no diesel flow lubricating those components. Might be a bad idea but wanted to throw that out there.
 

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Don’t know if this helps but I read that a person is supposed to spray some lubricant in the AFC rubber vent tube annually to keep corrosion down and lubricate the AFC assembly. AFAIK there is no diesel flow lubricating those components. Might be a bad idea but wanted to throw that out there.
I never heard that but I was thinking that it might be needed, never had to lube my old pumps AFC but it did leak a tiny bit of diesel so......
 

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Discussion Starter · #20 ·
The AFC is the diaphram thing with four screws? I see the tube from the intake and the small vent tube. Hard to spray in that little tube. (I didn’t try yet) I’ve been fixing other unrelated stuff on the truck from the trip. I need to do some baseline driving on a select road to make sure what happens when I make a change.
 
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