67RModel Posted July 2, 2022 Share Posted July 2, 2022 (edited) On my 1994 RD with EM7 there is this gadgetry. I am wondering if it’s really necessary. I have never really seen it on any other trucks newer or older and quite frankly I have never used it even when cold starting and the truck starts fine without using it. The thing is after sitting for any length of time the truck is out of air and can’t cycle the air cylinders anyway. Also, if you were to use it the cylinder on the bypass duct crossing over top of the engine won’t return to closed when it’s switched to “off”. You have to tap it closed after you turn it off. I just see it as a more leak paths for boost air to escape from or leak past the bypass valve. Can I eliminate the whole system? Should I? What’s everyone else’s experience with these? I’m just looking for any information out there on this setup….. Edited July 2, 2022 by 67RModel Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/ Share on other sites More sharing options...
mrsmackpaul Posted July 3, 2022 Share Posted July 3, 2022 New to me Paul 1 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-501956 Share on other sites More sharing options...
Hayseed Posted July 3, 2022 Share Posted July 3, 2022 31 minutes ago, mrsmackpaul said: New to me Paul Me Too, Paul. Quote "Be who you are and say what you feel...Because those that matter...don't mind...And those that mind....don't matter." - Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-501957 Share on other sites More sharing options...
Joey Mack Posted July 3, 2022 Share Posted July 3, 2022 so does it pull hot air off the exhaust manifold, for warming up the engine? I would like to think the valve is in the bypass position when cold, and then when air pressure is up, you can switch to 'normal' I dont know, just curious.. jojo Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-501966 Share on other sites More sharing options...
theakerstwo Posted July 3, 2022 Share Posted July 3, 2022 I have seen cement mixers with this on them and i am thinking it just to by/pass the cooler when not under power to keep the intake air warm.It does not take warm air off of the exhaust but only keeps the cooler from cooling the intake air when not needed .I see no problem with removing it. 1 1 Quote glenn akers Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-501969 Share on other sites More sharing options...
fjh Posted July 3, 2022 Share Posted July 3, 2022 Not necessary !This was developed for real cool climate warmup believe I have wired a few of these closed !It by passed the after cooler for quicker warm up rather usless to the average guy! 2 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-501970 Share on other sites More sharing options...
Popular Post 67RModel Posted July 3, 2022 Author Popular Post Share Posted July 3, 2022 16 minutes ago, Joey Mack said: so does it pull hot air off the exhaust manifold, for warming up the engine? I would like to think the valve is in the bypass position when cold, and then when air pressure is up, you can switch to 'normal' I dont know, just curious.. jojo No. Exhaust manifold is not part of the system. All it does is block the CAC outlet, which is the air cylinder in the lower left of the picture. And simultaneously open the bypass duct, which is the smaller one in the upper middle of the picture. The bypass duct is fed from the pipe coming off the turbo leading into the CAC. So in my mind it’s just pushing compressed air (warmer than ambient and warmer than going through CAC) straight into the engine to aid with starting? Kind of a novel idea I don’t know if it helps at all as I never really start this thing in cold temps and it’s stored in a heated garage anyway. It just seems to me to be a lot of nonsense for no benefit. Thoughts? 2 1 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-501971 Share on other sites More sharing options...
Mark T Posted July 3, 2022 Share Posted July 3, 2022 I too have seen these on mixers. Maybe in really cold climate (like you'd be pouring concrete there in the first place) a smaller HP engine might benefit from it on a cold start cause there's less fuel at full fuel throttle position ??? It'd have to be pretty cold to need it. A Mack engine in anything much above fair condition usually starts easy in the cold. Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-501996 Share on other sites More sharing options...
67RModel Posted July 4, 2022 Author Share Posted July 4, 2022 2 hours ago, Mark T said: a smaller HP engine might benefit from it on a cold start cause there's less fuel at full fuel throttle position ??? There could be some validity to this because my E7 is factory 250hp. I don’t think there were any ratings lower than that for the E7. Either way I am going to do away with the whole setup while I’m installing a boost gauge…. 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-502013 Share on other sites More sharing options...
Joey Mack Posted July 4, 2022 Share Posted July 4, 2022 you may want to take it off, with care and box it up.. someone may want it and be willing to shed a few dollars.. plus you are not throwing hard to find parts in the trash as I still see guys do.. just a thought... jojo 1 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-502015 Share on other sites More sharing options...
fjh Posted July 4, 2022 Share Posted July 4, 2022 12 hours ago, Joey Mack said: you may want to take it off, with care and box it up.. someone may want it and be willing to shed a few dollars.. plus you are not throwing hard to find parts in the trash as I still see guys do.. just a thought... jojo Yup I got a shop full of junk that MAY have a use some day😡 ! at some point something has to go! I have an old vintage lathe I no longer use I want rid of Can't sell or give it away! Has Dozens of accessory's! It may have to go to the scrap guys! Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-502050 Share on other sites More sharing options...
Joey Mack Posted July 4, 2022 Share Posted July 4, 2022 (edited) I too have a bunch of parts, its getting smaller.. I had a bunch of old Ford car engine parts that I rescued from a bulldozer, I was able to sell a lot of it at a major Swap meet event near me, I sold them cheap, but they went to good homes, and not back to China in little pieces, only to be resold to us as new junk... I wish I could find a place to bring my 'core' parts.. I hate to trash them, especially because finding the replacement part was an effort.. jojo Edited July 4, 2022 by Joey Mack Poor spelling Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-502052 Share on other sites More sharing options...
67RModel Posted January 5, 2023 Author Share Posted January 5, 2023 Ok I try to always follow up on threads I start. Anyway I got to working on removing this system from my truck. I started with removing the switch, indicator lamp and associated air plumbing in the cab. What I’m a little stumped on is what the valve in the first picture is? I will preface that question with how the switch was plumbed behind the dash. There is a large maybe 5/8” airline coming from I assume the air tank into a tee. Out of one branch of the tee goes to the air gauge. The other branch went to the switch. If the switch was turned “on” air would be sent to the valve in the first picture. The line went into a tee that was on the back of this valve and out of the other branch of that tee a line went to the cylinders on the bay pass duct. You can see there is a 3/8” plug in the back where the tee used to be. There is also a line going from this mystery valve to what I think is the aneroid (spelling?) valve on the intake manifold for the puff limiter in the second picture. The left and right sides of the valve in question are just dumping to atmosphere. Is it a quick release valve for when you flip the switch to “off” and/or when the manifold pressure gets high enough to dump the air on the puff limiter? Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-519994 Share on other sites More sharing options...
Onyx610 Posted January 6, 2023 Share Posted January 6, 2023 Start at 10:00 2 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520121 Share on other sites More sharing options...
67RModel Posted January 6, 2023 Author Share Posted January 6, 2023 (edited) 10 hours ago, Onyx610 said: Start at 10:00 Thanks. Ill have to dig into it a little more to try and understand how/why that CAC bypass is plumbed into that valve. I assume the valve I am asking about it the LDA valve? Thanks. Edited January 6, 2023 by 67RModel Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520142 Share on other sites More sharing options...
Joey Mack Posted January 6, 2023 Share Posted January 6, 2023 (edited) Doesn't one of the air lines go from the intake manifold to the front of the injection pump? If so, I believe it actes like a reversing relay, and high boost pressure, operates the Number valve to push the rack back.. if I remember correctly.. it helps to keep from over boosting the engine.. Jojo Edited January 6, 2023 by Joey Mack Pore cell fone sperring 1 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520143 Share on other sites More sharing options...
67RModel Posted January 6, 2023 Author Share Posted January 6, 2023 1 minute ago, Joey Mack said: Doesn't one of the air lines go to the front of the injection pump? If so, I believe it actes like a reversing relay, and high boost pressure, operates the Number valve to push the rack back.. if I remember correctly.. it helps to keep from over boosting the engine.. Jojo Joey, Yes. In the second picture the airline painted in gray that goes out the left side of the picture from the manifold goes to the injection pump to limit rack travel before manifold pressure gets high enough to burn all the fuel from fully open rack. The line coming in the bottom of the second picture to the manifold I think comes from the transmission to keep the rack from opening fully until you switch into transmission high range (I have not confirmed this yet though). I'm just wondering now if I should remove that plug I put in and put tank air to it or tank air via the parking brake valve like the old puff limiters were set up. I'm just not sure schematically what the valve in the first picture does or what its "looking for"..... Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520144 Share on other sites More sharing options...
Joey Mack Posted January 6, 2023 Share Posted January 6, 2023 So the tranny line is a torque limiter? Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520150 Share on other sites More sharing options...
Onyx610 Posted January 6, 2023 Share Posted January 6, 2023 The vid answers a lot of questions haha Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520151 Share on other sites More sharing options...
67RModel Posted January 6, 2023 Author Share Posted January 6, 2023 (edited) 16 minutes ago, Joey Mack said: So the tranny line is a torque limiter? That is my understanding of it. Well at least how the older style puff limiters worked on the E6s. You got full rack on start up (to aid with cold starting). As soon as you released your spring brakes air was sent to the puff limiter until manifold pressure (boost) was sufficient for full rack. Also, If you had a Mack transmission with lolo gears you wouldn't get full rack until the transmission was in forward high range. I'm not sure about this LDA system and why that valve is mounted up off the manifold. The older style puff limiter valve was tapped directly into the manifold. Edited January 6, 2023 by 67RModel Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520152 Share on other sites More sharing options...
fjh Posted January 6, 2023 Share Posted January 6, 2023 6 hours ago, Joey Mack said: So the tranny line is a torque limiter? yup Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520163 Share on other sites More sharing options...
67RModel Posted January 7, 2023 Author Share Posted January 7, 2023 OK I got this figured out now thanks to the video @Onyx610 posted and actually having time to sit down and watch it. The video along with some other sources got me all straightened out. Mechanically governed E7s use the LDA system and not the puff limiter system. For those that don't know and want to know here goes: In a cold start scenario the puff limiter system (think E6 and possibly older) is full rack by default. Rack travel becomes limited once you release the spring brakes and air is sent to the injector pump. Once boost pressure is sufficient for full rack the boost pressure overcomes the air pressure supplied by the parking brake valve via the reversing valve that is tapped directly into the intake manifold. Boost pressure and chassis air pressure are always hydraulically "battling" each other in the reversing valve for control of the air cylinder in the injection pump. In a cold start scenario the LDA system is limited rack by default. There is no reversing valve at the intake like the puff limiter system. The LDA system just has a line tapped into the intake and constantly adjusts rack travel based on boost pressure alone. No compressed air is involved. In a cold start scenario limited rack is not desirable so a workaround is needed. That is the purpose of the valve in the first picture a few posts back. It is a Bendix SV-1 Syncro Valve. When you flip the dash switch to "on" for the CAC bypass, tank air (assuming it hasn't all leaked out) is sent to the SV-1 valve as well as to the two cylinders in the bypass duct plumbing. The cylinders simultaneously close the CAC outlet and open the bypass duct allowing warm compressed air to directly enter the intake manifold. The air sent to the SV-1 valve is regulated down to whatever maximum boost pressure is and passed down and connected to the the tee fitting in the intake manifold where the LDA is tapped into. Thus, the LDA is "fooled" into thinking boost is max and full rack is available before you start cranking the starter. Once the truck warms up a little the CAC bypass can be switched off, the air cylinders cycle back to their normal positions, boost air begins passing through the CAC normally, the air going to the SV-1 valve is exhausted, and the LDA goes back to sensing whatever the actual manifold pressure is. Of course it doesn't stop there. Both systems utilize a torque limiting valve if the truck has a Mack transmission. Once running, if the transmission is put into reverse and/or the low forward gear(s) the torque limiting valve is activated. It is piped from its location on the transmission up to the reversing valve (puff limiter) or to the tee where the LDA is tapped into the manifold. Once its activated it dumps the boost pressure to atmosphere that would normally build up in the system and allow full rack travel. By doing this rack travel is limited in both systems to protect the drivetrain in the low and reverse gears. Once the shift rails are moved to select a higher gear the torque limiting valve closes and allows boost pressure to build up and allow for full rack travel in the injection pump. Below is a picture taken out of my E7 book explaining that all fully mechanical E7s made after 1991 have the CAC bypass setup installed by default. I assume the VMAC trucks can electrically advance the timing during cold startup making this system not necessary for them. I will say that I have consistently been able to start my truck down into the low 30s high 20s temperature range without using this system and it fires up very quickly. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520218 Share on other sites More sharing options...
Onyx610 Posted January 7, 2023 Share Posted January 7, 2023 Damn! Id say you got it figured out! Hell of a write up sir….🍻 Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520219 Share on other sites More sharing options...
mrsmackpaul Posted January 7, 2023 Share Posted January 7, 2023 I wonder if the intercooler bypass is for running not starting There must be temp when the air is to cold and gets to cold to be efficient, we will never see this in Australia but places like Canada and parts of north America and Europe and Vlads part of the world and up into Siberia this would be a issue I wonder if the 6x6 Macks Australia sent to Antarctica had the bypass ? A few were for sale recently, should of bought one just find out, didnt know anything about this then Sorry side tracked this thread, but the brain is running at 100 MPH now lol Is there anywhere the R model hasnt been, they must be the most versatile truck ever built Sorry I'll take myselfoff to the naughty corner lol It doesn't look like these are coolpower trucks Have never seen a chassis mounted intercooled Flinstone Mack Paul Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520232 Share on other sites More sharing options...
mrsmackpaul Posted January 7, 2023 Share Posted January 7, 2023 And now that I'm looking, I have just noticed these are air start, there goes my "air start will be no good in the sub zero climate" theory Vlad you need a air start Mack A couple of photos and I'm loosung the plot 😂 Paul Quote Link to comment https://www.bigmacktrucks.com/topic/70046-charge-air-cooler-bypass/#findComment-520233 Share on other sites More sharing options...
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