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| Truck & Diesel Mechanic Forum - ASE Medium/Heavy Duty Truck Forum :: Forums :: Caterpillar | |||
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 Shall I re-do the performance dyno after axle and manifold change? |
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| tracer |
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  Joined: Sat Mar 06 2010, 10:11AM Posts: 7 | Hi, everybody. I have a 2004 CAT C15 Acert, which was dynoed by CAT in Concord, ON in 2008. The thing had 550 HP at 1,425 RPM which translates into appr. 2000 lb-ft of torque. The dyno tuning was done with 3.73 axle ratio and standard manifold (it had leaks too). In December 2009 I replaced the old manifold with an extrude honed one (130 cfm extra air flow) and upgraded the axle ratio to 3.42. Before the truck did 59 MPH at 1370 RPM (digital speedometer). With the new ratio, I do 62 MPH at 1330 RPM. Because I"m in Ontario, Canada, the truck has to be governed at 65 MPH, which doesn't leave the truck a lot of RPMs to play with. Either that or this new trailer I"m pulling is really bad on fuel, but starting in January my fuel mileage went down from 6 to 5.5 MPG with 45,000 lb load. (I do drive 62-63 MPH now instead of 59). CAT checked air-to-air hoses for leaks and found some, but the truck still gets bad fuel mileage. I drove it bobtail this morning to check the power and when I'm at 62 MPH (1,330 RPM) nothing happens when I push the fuel pedal, I mean there's a big delay. Before the December repair, my maximum boost was 48 (heavy load, big hill) and the truck was very quick. I rarely see 45 psi now. SHALL I RE-DO THE DYNO TUNING WITH THE NEW SPECS (manifold and axles) or is the sluggish performance and poor fuel mileage caused by something else? Thanks very much! Read my "Trucking ahead" blog | ||
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| wcdiesel |
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   Posts: 227 | You need to plug in and change your Engine / Gear parameters to suit your new ratio - then you,ll get your fuel back Regards David wcdiesel | ||
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| tracer |
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Joined: Sat Mar 06 2010, 10:11AM Posts: 7 | I did that at the local CAT right after I changed the rears. 512 rev/mi tires, 0.73 top gear ratio, 3.42 axle ratio 512x3.42x0.73= 1278 RPM at 60 MPH. And that's what my speedo shows. With 3.73 ratio, the speedo showed 1,394 RPM at 60 MPH. It's either the sliding tarp trailer or for some reason the engine doesn't make as much turbo pressure as before. I booked an appointment for diagnostics at the CAT and their guy is going to ride with me while his laptop is hooked my the ECM. I should know the answer tonight  Read my "Trucking ahead" blog | ||
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| wcdiesel |
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Posts: 227 | Sorry tracer , did,nt know you had already changed the specs - now that you,ve changed manifolds get your cat bloke to check boost sensor , atmospheric sensor and oil pressure sensor Regards David wcdiesel | ||
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| tracer |
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Joined: Sat Mar 06 2010, 10:11AM Posts: 7 | sounds like a plan. i rode with a tech in my truck yesterday but the guy couldn't tell me anything about fuel pressure. the boost went up to 44 once he cancelled the speed limiter. the maximum reading i saw with the old manifold and 3.73 axles was ... 49! that's with a heavy load going uphill. i'll definitely check the sensors. thanks! for now i want to try driving at 1,360 rpm as opposed to 1,330 I did before and see if that makes any difference. if interested, see my blog for more details about the failed CAT "test" Read my "Trucking ahead" blog | ||
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| wcdiesel |
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Posts: 227 | Must be a problem with link - could,nt read your blog page ? I hope the cat bloke reset your new cruise and speed limiter parameters !! Don,t know your serial number but if you have the early filter head you need to check fuel pressure under load ( as the cat bloke should have done on your road test ) and I,ve seen the mentioned sensors play up when air flow is increased Regards David wcdiesel | ||
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| tracer |
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Joined: Sat Mar 06 2010, 10:11AM Posts: 7 | Thanks to Admin for fixing the link to my blog. Spent 2 hours at CAT yesterday and they didn't find anything in the engine that might have caused the boost to go down (see the blog for details if interested). My next move is to save 800 bucks and do another performance dyno at CAT: I think I screwed up the fuel/air ratios by putting in this extrude honed manifold with its 130 CFM extra air flow. Read my "Trucking ahead" blog | ||
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| Moderators: Master Mechanic, popskull, Muffler Bearing, irishniners, hdtrktch, wcdiesel, proffesor |
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