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 6/23/2004 8:41 AM
 
posted June 23, 2004 10:29 AM I would like to know of anyone who is having power problems with the C7 Cat engine. I have a low power issue and the motorhome has no get up and go from 5 mph to 40 mph, I know others must be having this problem Jim Jim

Jim
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 7/21/2004 7:24 PM
 
Jim,
Here is an update on my C7.
We spent better part of 2 weeks at F/L in Commerce City, in north Denver. They found the rear brakes were dragging!!!! Seems the F/L factory did not adjust properly when building chassis. CAT gave F/L the latest firmware upgrade for the ECM and said my fuel injectors were ok, the new larger type. F/L also tweaked two different parameters in the ECM & reset the transmission ECU, as the Allison had learned only freeway driving mostly from the 1146 miles from Forrest City, Iowa to San Antonio, TX. Finally the rig started to drive MUCH better...albeit still with a slow start.So we took a test drive Thursday before out I-70 west from Denver and up the 6 mile 6-8% grade...the rig still does not like to climb hills!!!! It started up the grade from ~60 mph, pulled ok in 4th at 55, then slowed to 50, then 45, then 40 and finally downshifted to 3d gear at 40 mph...finally wound up in 3d gear at 34 mph and 18 wheeled trucks started passing me!!@@##
My old rig would pull this same hill in 4th gear at 45 to 50 mph!
The loal CAT rep said that with the new injectors and the latest firmware update in the ECM...that was all CAT could do. I think the CAT C7 engine is ok...I believe it is just tweaked 'down' in the ECM paramters for EPA reasons.
I got the new rig weighed at Flying J....30,640 lbs. well within the 32,000 GVWR but still a pretty good load. I then did an analysis of pounds per HP and pounds per Lb-Ft of torque with my old rig and this new one....ratios were nearly identical...so my new rig should climb ever bit as good as my old rig....23,450lbs. (actual wt.) to 275 HP and 660 Lb-ft. on my Cummins ISB 5.9 vs the new rig of 30,640 to 350 HP and 860 Lb-Ft.of torque. I think CAT had to tweak it 'back' to meet the new 2004 EPA air standards.
I remember talking with several Allegro Bus owners of '99 to 2001 rigs with the older CAT 3126 series and they all said the motor had plenty of power and getup & go, and still got 8 mpg! The old Allegro Buses were on a 30,000 GVWR chassis.

Rudy

Rudy Morris
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 7/21/2004 7:27 PM
 
Jim and others;
Another update - we have another appointment back at F/L in Denver for 8-9-04 for yet another CAT ECM update (if they get it ready in time).
According to the current July Motorhome magazine pg.90,...Power Train Q&A by Ken Freund, he quotes a formula he recently recv'd from GM that figures the H.P. required to climb different grades at various speeds. It takes the actual wt. of your rig divided by 37,500 X mph X %grade.
In my case, actual wt. = 30,640 / 37,500 X 50mph X 6% grade = 245 H.P. I'm assuming that is actual brake HP to the road, not advertised HP.
According to a CAT engineer, the C7 should put out around 250hp to the pavement.
Therefore, I once again conclude that the C7 should be able to climb a 6% grade at around 50mph. As noted here in this thread, mine climbs an extended 6% grade at 37mph without the tow car and 34mph with the towed.
The CAT C7 is not performing up to expectations! Too much smog control.

Rudy Morris
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