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baptistbusman
Advanced Member
USA
301 Posts |
 Posted - 04/14/2007 : 5:00:24 PM
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Man, one of my new CV200s is really causeing me some headaches. 94 GMC 366 engine.
I noticed on one of my first trips with it, when I come to a stop and the bus idles down, it will idle so low that the oil pressure warning will go off. Also the idle will surge, like rev up and then rev down and it will just sit and do this with the bus in gear at a stop. Now the bus has a "high idle" button, and when the engine is surging like this the high idle button will not work.
I was messing around yesterday and found a corroded connector on the pig tail that hooks into the oil pressure sender. I put some electric type grease on the sender pins and plugged it back in, high idle worked then, and the engine no longer surged down low enough for the oil pressure warning to go off.
A little later i got back in the bus, started it up, and the high idle wouldnt' come on again, and the bus surged at an idle and the warning came back on.
Now, my question is, does the oil pressure sender have something to do with the engine idling or am i going in the wrong direction with my diagnoses? Is there an actual sensor that controls the high idle on the throttle body? |
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ModMech
Top Member
USA
948 Posts |
Posted - 04/14/2007 : 5:39:54 PM
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As I recall, and please forgive me it's been a while, the EOP switch also feeds the fuel pump. So, the fuel pump does not work unless you have oil pressure. Sort of a safety feature that they should not have (actually IF it's wired this way it violates FMVSS for School Busses as they CANNOT have any form of engine shut down system).
But, I don't have an wiring diagrams to look at. I just recall not getting any power to the fuel pump unless the Low Oil Switch was connected and working. |
If you want customer service, you NEED an International! |
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NWCROWN
Advanced Member
USA
461 Posts |
Posted - 04/14/2007 : 10:32:33 PM
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I want to say that several GM front-wheel-drive cars are designed that way, where the sending unit affects operation of the fuel pump.
I recently went through something similar involving a coolant temp sensor on my 1984 Oldsmobile. It was corroded, so I cleaned the connection, it worked temporarily, but was affecting idle mixture. I replaced the sensor, which utilized a redesigned connector, and it cured the problem.
I have found that if a connector is corroded, a lot of times the sensor is corroded internally as well. I occasionally would disassemble a sensor, usually coolant, to find corrosion that migrated from the connector end. This was the case with my Olds, I have encountered this with GM oil pressure sending units also. |
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baptistbusman
Advanced Member
USA
301 Posts |
Posted - 04/15/2007 : 11:49:19 AM
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i changed the sender, fixed the problem with the pressure dropping, however the high idle will not work. Is there just a specific switch that operates the high idle?
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1 Timothy 1:15 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief. |
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JC Theriault
Top Member
Canada
1326 Posts |
Posted - 04/15/2007 : 6:33:37 PM
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I haven't been around GMC school buses in years and was just wondering why you'd want the high idle used on a gasoline engine like the 366. Anyone I've worked for would complain if drivers ran gas engines at high idle. Thye heat up fine at idle engine speed unlike a diesel and the oil pressure should stay up in the safe area without the added RPMs.
JC |
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baptistbusman
Advanced Member
USA
301 Posts |
Posted - 04/16/2007 : 05:39:13 AM
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| Well, there is a switch there, and I really like all of the options working, plus, it seems this high idle switch is tied into something else. |
1 Timothy 1:15 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief. |
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torque
Advanced Member
Canada
358 Posts |
Posted - 04/16/2007 : 11:05:29 AM
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[quote]Originally posted by JC Theriault
I haven't been around GMC school buses in years and was just wondering why you'd want the high idle used on a gasoline engine like the 366. Anyone I've worked for would complain if drivers ran gas engines at high idle. Thye heat up fine at idle engine speed unlike a diesel and the oil pressure should stay up in the safe area without the added RPMs.
It's not good for *any* engine to idle, combustion chamber temps drop and you do not get complete combustion of fuel. Raw fuel, gas in this case wash away oil on the cylinders, enters the cat and raises it's temperature. Raw fuel also gets past the rings and dilutes the oil.
Other reasons, alternator works better, keeps up better with demand from heaters.
I wish I could help with the high idle switch, we only had one of those and it's gone now so I can't even go and see how it works. |
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International-9.0
Advanced Member
USA
459 Posts |
Posted - 04/16/2007 : 4:28:46 PM
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| I agree 100% with Glen. Extended low idling is not good for any engine. A bus that has lots of lights and heaters going will need more electricity than the alternator can produce at idle. All buses should have a throttle control. I really wish that my car had one for warming up on cold mornings. |
Edited by - International-9.0 on 04/16/2007 4:30:25 PM |
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Wolf0r
Top Member
USA
2181 Posts |
Posted - 04/18/2007 : 12:37:10 PM
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| Hey Baptist man check your brake lamp switch. The oil pressure switch does NOT kill the engine. Check your exhaust manifolds, when they leak the engine idles crappy. |
“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson |
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Cody
Top Member
United States
1630 Posts |
Posted - 04/18/2007 : 2:09:02 PM
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I got a 1991 Chevy and it has a cable operated throttle control. I've been around so many newer GMs where the high idle switch has broken, so I feel the cable operated one is a little more reliable
And Rob is correct, check your exhaust manifolds, mine leak like crazy and the bus is slowly starting to idle like crap, but once revved up its fine. |
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baptistbusman
Advanced Member
USA
301 Posts |
Posted - 04/18/2007 : 7:23:05 PM
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Yeah, have had to change many exhaust manifolds in the last 8 years on the 366's. Usually what has happened is that when a school district replaces them after they crack, they reinstall them with the manifold gaskets, which gm doesn't suggest. After I just install them with no gasket, they never fail.
The engine has never died or anything because of this, i fixed the problem wiht oil pressure going down, but my main problem is trying to figure out what controls the high idle on the bus. Is there a switch on the throttle body for this??? My main problem is figuring out why the high idle works sometimes and why it doesn't sometimes. When high idle switch will work, the engine will not surge, but when the high idle switch wont work, the engine surges. |
1 Timothy 1:15 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief. |
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baptistbusman
Advanced Member
USA
301 Posts |
Posted - 04/19/2007 : 05:31:40 AM
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| Hey Wolf0r, I tried to reply to the email you sent me, however it was returned undeliverable. Go ahead and send what you have over when you get some free time, thanks |
1 Timothy 1:15 This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief. |
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Oil Sender/High Idle
