While driving on highway at 70 mph with cruise on my 98 GMC Jimmy jerked and check engine light came on. I turned around and drove back home - around a 20 minute drive - cruise worked, Jimmy ran fine, but check engine light stayed on. Jimmy is a 2 wheel drive with about 105,000 miles. Any suggestions? Thanks
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Sounds like you have a cylinder misfire. Is check engine light on ?, Have you had the vehicle somewhere to get a code scan? My assumption is that you have an ignition problem that is causing the rough idle and jerk feeling while driving.
Take the vehicle to a shop and have them diagnose the driveability problem that you are having.
code p0320 refers to cam shaft position (CKP) sensor/engine speed (RPM) sensor--circuit malfunction=== causes --wiring--CKP/RPM sensor ---ECM
because the engine runs ok until it is on cruise control I would be investigating the RPM sensor for a fault
The cruise control takes its control from the RPM sensor and if that circuit is interminable the the cruise control doesn't know what rpms to maintain.
make a mixture 1 liter two table spoon of salt in bottle with spray engine idle spray your mixture not too much and see if you have spark on wire ,coil you won't see it if too much mixture and about spark plugs you could change it too you have a misfire
This is my drive cycle a generic drive cycle i have used many times over the years and it has never failed me most drive cycles are too specific and impossible to adhere to for most drivers follow these steps exactly 1. make sure all codes are cleared and no check engine light is on 2 make sure the fuel level is between 1/4 and 3/4 full (this is part of the enable criteria for the evap monitor to run ) 3 let vehicle set overnight 4 start engine and let idle until the temp gauge is in the middle (this cold start enables the evap monitor and runs the O2 sensor heater test )5 drive vehicle around town avoid the highway stay at below 50 mph and when stoping at lights remove your foot from the gas and coast from around 50 to about 10mph or less if possible this will run the EGR monitor after about 3 to five miles of this proceed to the highway or freeway and travel over 50 but under 70 mph for about 3 to 5 miles this will run the catalyst test provided the O2 monitors passed if they didnt you will have a check engine light on before this point also i do a coast down on exit ramps (no braking) they make great places to get that EGR to run ONCE YOU START THIS PROCEDURE DO NOT KILL THE ENGINE OR SOME OF THE TEST WILL FAIL TO RUN
Sounds like the transmission is not shifting into a higher gear. 2,500 to 3,000 rpm would be more realistic for a highway cruising speed. The higher rpm may not be a big deal as far as the engine is concerned but it will hit you pocket book pretty good when you loose the mpg that you should get.
I would personally either limit your driving until it can be checked or at least slow down so that the RPMs are in the range listed above.
Let me know what they find, my curiosity is peaked!
Your dealership should have seen any underlying codes. Most Cruise controls I've worked on are used on the vehicles vacuum. that is where i would start, because on a grade your engine uses more vacuum pressure thus taking from some where else.