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e-7 427 erratic throttle response


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hi,sorry for the bad puntuation,i'm not a typer. i have a 1995 cl-700,and i'm not sure if it has a bad throttle pedal,or some other electrical issue,the jake brake,now i'm not sure if it is an actual "jacobs" brake or if it's a dynatard, what it does,is you can have it on "high" and sometimes it does nothing or very very little to slow you down.sometimes it will work like it should, it mostly won't work unless the engine is at 180 degrees.the other issue is with the throttle mostly it will rev up to 2100 in the lower gears,then once you get to 7th and higher it is slow response and seems like it cuts out at about 1600,if you "pump" the pedal it will sort of throttle up but very slowly. it's an E7-427. it has supposedly had the valves adjusted,and it's had cam sensor put on it. some of the time the truck is an absolute powerhouse,then all of a sudden the power goes away and it slowly throttles up.it's an electronic throttle pedal,and i've been oiling the hinge on floor mount because the pedal it hard to push from an idle. anyone have some ideas for me?

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I think to solve this you need to put a fuel pressure gauge on the supply line at the pump ( I would think that there should be a test port to use) if fuel pressure stays good then check out the throttle pedal. if it has a jake the actuator housing will have there name on it. have they been kited ? (maintainer/ overhaul kit) sounds like you either have a faulty solenoid or internal oil leak in the jake oil circuit

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no,not the roller part that works fine,its the hinge at the floor that makes it stick.so i've been oiling that. i know this will probably sound crazy, but about a month ago i was running down a county highway truck was running perfectly, started to slow down with the jake for a stop,again running perfectly,stopped at the corner, go to take off,no power at all, sputtering,smoking blue as can be smoke, acted just like it was gelling up, go to the side of the road,engine seemed like it was trying to run with the jake on. shut it off change fuel filter,bled injectors 2 cyl, were getting no fuel, took mainline off blew it back into the tank. primed pump and bled injectors again this time all fuel. shut it off, restarted same thing,chugging, misfire, and smoke like hell, i had it about 1/4 to half throttle,and i guess frustration by this point got the better of me so i mashed it to the floor and let immediately off ,you know basicly slapped it down,3 times,and wala ran perfect. it has run good up until recently when acceleration gets erratic, the jake has always been hit or miss,but the throttle pedal has been sticky as long as i've been driving it.the floor is clean,no dirt build up on it.

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You can have a cracked washer in one of the injection pump delivery valves. Depending on which pump you have they can be replaced and the delivery valves resealed. Also can be an econovance solenoid which can be replaced easily.

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no warning lights at all when it acts up, also the truck will not idle more than about 2 min, if you don't bump the idle up, i had it at a mack dealer they replaced timing sensor? or crank sensor, truck used to idle very slow only about 350 rpm,so they re calibrated it to 700 but will still shut down if you don't bump up idle,they didn't have an answer as to why.

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Anybody else notice the rpm in the first post? This is an 1800rpm engine, its not going to accelerate quickly past 1600. 1800 should be the end of fuel delivery but as most of us know an 1800rpm Mack will usually run a little higher than spec. If you keep the rpm under 1800 say 1600-1750 and shift it will pull better than winding it out.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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no warning lights at all when it acts up, also the truck will not idle more than about 2 min, if you don't bump the idle up, i had it at a mack dealer they replaced timing sensor? or crank sensor, truck used to idle very slow only about 350 rpm,so they re calibrated it to 700 but will still shut down if you don't bump up idle,they didn't have an answer as to why.

Sounds like a fuel pump issue to me, if you have a good pump shop around to check it out they might find your issue.

"Any Society that would give up a little LIBERTY to gain a little SECURITY will Deserve Neither and LOSE BOTH" -Benjamin Franklin

"If your gonna be STUPID, you gotta be TOUGH"

"You cant always get what you want, but if you try sometimes you get what you need"

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i had no clue it should top out at 1800, some one has had they're fingers in it, first 427 i've had, i've had older 237,and 350's mechanical throttle, thanks for telling me it should cut off at about 1800, i took the connection off at the pump and it was a little grungy,dirty. i cleaned it and it's a lot better the jake brake is still hit and miss. what do you do to test the solenoids? it has 2 on the top of the engine so i would assume one runs med, and both run high setting. i'm pretty new to trying to figure this out. will the econovance affect the jake brake coming off or on, the connections to the solenoids are clean and tight, if it was bad seals is that something you would have to take it apart and look at? or is there a way to check ? i've looked at the harness and there isn't any bare spots or chaffing, i guess there could be a broke wire maybe,but i don't think so. any advice or input is appreciated.

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Wiggle the wiring and connector while the truck is running and see if it faulters. As for the jakes you can apply 12v to the solenoid connector and it should engage. It should disengage whem the 12v is removed. The econovance does not affect the jakes directly but will cause poor engine brake performance if it is not advancing the timing.

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ok,i put power to each solenoid 1 at a time, each one will activate, if i put power to both at the same time, it sounds/runs the same as it does with only one powered,i don't know if the first owner did anything to it for maintenance, i know the second owner did no rebuild kit but he did tell me that the jake always seemed kinda weak so i guess maybe that would be the route to go? the truck has only been back out on the road full time since dec,prior to that, it sat for months at a time for about 4 years. it has just over 9,000 hrs on it. i should have mentioned that part right at the beginning. probably would have been more helpful.

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i'm not 100% sure that it is a jacobs brake,on the top of the engine there is 2 separate let's say "packs" they have 1 solenoid each, you could take each off individually it looks like. i haven't found any numbers or markings on them.the under those, is a plate maybe 2 in,thick. some where along the way somebody has had they're fingers in the wiring,down at the injector pump where the electronics for the throttle hook up there is 4 wires not counting the ground wire,the wires are a tangled mess,that go from 4 to 2 then 4 wires run up the side of the block up to top of engine then 2 are cut and the 2 remaining go to each of the solenoids.also for some reason there is an off on switch on the shifter. the switch on the dash has to be on high setting or it does nothing. like i said in one of my previous posts i'm very new to trying to fix my own trucks issuses,and i appreciate very much any comments,advice that i can get.

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sounds like they bypassed the pump idle switch and the driver used a on/off switch to run the brake with that said with the switch on and the dash sw. on hi do both solenoid have power ? then check low. you may have a damaged hi\lo sw. with low setting bad.

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well,here's what it'll do. you can have the shifter switch,"on" have the dash switch,"off" jake comes on like low-ish hit/miss. shifter switch,"on" dash switch on "low" jake works a steady low but every so often won't work at all. shifter switch "on" dash switch on "high" jake will come on everytime you release throttle, but some of the time it's full power, some times it's low,and some times it hit/miss. i've looked at the connections, changed the toggle switch on the shifter thinking that was bad,because it seemed that if i wiggled the switch it worked more often than not. i put a 20 amp switch on it maybe that's not enough? ive looked at the wires, the ground, as best as i can tell in the tangled mess of wire is solid and to the side of the head, could that be the cause of it, should the ground be to the frame instead. i'd like to put it back to original and get it working good, the hard part is every wire except the tangled splice mess is grey so that's really helpful,lol . the only thing that got better was after i changed the shifter switch is,when it's on it always comes on when you release the throttle, but it's a 50/50 shot whether it'll be on high. if one the solenoids was bad,how would you determine if it is? i can power them directly and they come on, also,when you have it on you can leave the toggle switch on, it will cut off at about 1100/1000 rpm,and idle normally. the only part i haven't looked at yet is behind the dash, could it be that simple,that the darn dash switch is bad,and causing the interference? i've been hesitant to pull dash out because after the tangled mess by the pump, i'm worried there'll be a rat's nest there too.

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