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BlondeBulldog

'97 E7 427 Intermittent Low boost & High EGT

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Hello!

I've got a '97 Mack CH613 with the E7 427 (V-Mac II) and 13spd Mack transmission. I've been having an off and on problem with low boost and high EGT for about a year now. The truck has 350,000 original KMS on it (about 220,000 miles) and I'm the second owner. I have owned it for about 5 years now.

I use it on my farm to pull a hi-boy hay trailer and to pull a tandem axle grain trailer. The last couple of weeks I have been delivering grain on a 320 mile haul round trip, with about 20 metric tons (44,000 lbs.)

On one trip last week the engine wouldn't make much more than mid 20's for boost, when it's usually over 30 lbs. and the pyro was running between 1000 and 1100 degrees Fahrenheit, when it usually never tops 900 degrees. After driving about 55 miles I was able to stop and shut the engine off, and check for any intake/exhaust leaks. None found, grabbed some lunch and fired up again and everything was back to normal, over 30 lbs of boost and exhaust temp. below 900. Made a couple more runs that week and everything was fine. Loaded up and pulled out a couple of days ago and was back to mid 20's for boost and exhaust temperature approaching 1200 on a long hill. Again stopped after 55 miles, had lunch and let the engine cool off. Checked for plumbing leaks, pulled the aircleaner element, removed the aircleaner elbow and spun the turbine: no obvious rough spots or any sticking, put everything back in place. Fired up and delivered that load all the way there and back with low boost and high EGT.

Earlier this winter I was coming back from the truck wash and the truck lost all boost and was making some pretty terrible noises while trying to accelerate. Called the Mack techline and was informed that I had probably bent a connecting rod due to "filling the intake with water" or else had a major electronic fault. In a panic I had the truck hauled to Redhead Mack in Lloydminster Saskatchewan the next day. They called me around noon and informed me that the truck was fixed and ready to go. The stealth exhaust brake had failed in the closed position thus closing the exhaust off and not allowing the engine to make any boost. Since parts are no longer available to fix it, they wired the exhaust flap open with some mechanics wire.

What has me scratching my head is: why does this problem seem to be intermittent? If there's an air leak, I.E. loose clamp, air compressor feed line worn through, cracked intercooler etc. it should be consistently low boost. NO?? Also if the engine is "de-rating" shouldn't it be cutting fuel which would in turn limit boost AND EGT temperature AND produce low power? The truck doesn't really seem to be short of any power when it's low on boost, but the exhaust temperature is much higher than normal, leading me to believe that it's getting the proper amount of fuel, but not enough air.

Lastly, the electronic malfunction light only came on once during this timeline, when the truck was running normal, and empty about 20 miles from home. It shut off when the ignition was turned off and hasn't come on since.

Any and all comments/advice welcome! This is getting a little frustrating. I've made an appointment at Redhead for Monday morning, but at $135 an hour, I don't want them taking days and days trouble shooting this thing!!

Thanks!!

Later,

Marc

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Here is an issue we had last fall, truck one the jake brakes were coming on their own, ran terrible and we unplugged the wires and it ran great. Easy to tell though that it was the jake once we stopped, pulled the wires and it purred again.

Second truck was the exhaust brake butterfly valve, where the air ram connected it cracked and was slowly closing the exhaust brake. This caused low power and high pyro's. Finally we figured it out, pulled the floor board, and pulled the air ram

back and clamped it till we could fix it properly. But it looks like yours was diconnected already.

Winterfront also means high EGT's when its warm out.

Hopefully someone else here has some ideas for you.

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could check your hoses on the CAC and check your CAC. make sure there is no leak.

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Muffler baffel broken and sometimes gets blown up sideways blocking hole. I doubt thats it but I have seen happen, took me 2 days to figure it out!

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I think I solved it! Built a tool to pressure up the intercooler with an aircompressor and heard some leaks at the intake manifold side of the engine. Got new silicone type hoses for the turbo and manifold side of the intercooler. I also pulled the floor plate and built a strut to hold open the exhaust flap, the piece of wire that the Mack dealer used wasn't far from coming loose. :( While I was crawling around, I also found that the bracket holding the air dryer on was broken, welded that up and reinforced it, and changed the cartridge in the dryer. Now I know why most truckers are broke, if I had kept my appointment at the dealer I'm sure it would have been a couple of thousand dollars to troubleshoot and repair. That's not to say it would have been repaired properly either............ Took 'er for a short test drive yesterday and it seems to be back to normal. Gonna take another load down the highway today and we'll see for sure! As a sidenote: does anyone know what the diagnostic program for a laptop pc costs? I'm thinking that could be useful in the future for checking on electronic faults. As this truck ages the sensors are gonna fail, and it's gonna be a real PITA to track them down............

Later,

Marc

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I would look into removing the exhaust brake completely if the butterfly in the exhaust gets loose or rusts where it connects to the shaft it can move restricting the flow, I doubt it would cause low boost if anything boost would go up slightly by restricing the engine exhaust after the turbo. I think I remember having high EGT low boost issues a few times before on trucks coming thru the shop it was normally boost leaks but I also found some had air intake issues before the turbo limiting airflow causing the engine to run rich and get hot, things like old filters / hoses being sucked in and the interior coming apart on one and hanging down, a 97 ch has an air filter box on the firewall with aluminum pipes and rubber elbows so thats pretty sturdy. I would also clean the cooling stack top to bottom to make sure you dont have a plugged radiator/intercooler, you are correct about the high EGT limiting fuel on an ETECH if the temp gets high fuel is reduced dropping power and lowering boost to try to cool the engine and one cause is a dirty cooling stack.

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Everything seems back to normal or almost normal now. I'm making about 30lbs of boost @ wot pulling a hill at around 1500-1600 rpms, egt is around 900 degrees. Seems to be low on boost by a couple psi, but no big deal really. Guess it was the leaky intercooler plumbing. After 15 years, it'd be about time to replace those rubber connectors, no doubt!

Thanks for the help gentlemen.

Later,

Marc

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