Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
I am sorry for the long wait
at this point with NO codes at all and to NOT throw parts at this truck is a scan tool needs to be connected to this truck and monitoring current misfires on the live data list when it is missing and see if it registers a specific one or two cylinders misfiring
its a little odd on a 1999 truck to have a misfire and it not trigger at least a PO300 code
we have seen issues with the fuel injector spider cause this type of issue to sticking valves in valve guides case this type of issue
but at this point we need to see if it is a specific cylinder or not misfiring when it is acting up
it will still show misfires if your scan tool will show live data of the current misfires in the misfire data list or one of the data lists
you usually find out which cylinder is misfiring then connect a fuel pressure gauge and perform a fuel injector pressure drop while firing each injector with a scan tool seeing if all 6 injectors drop the same amount of fuel pressure
see if someone has a scan tool that can see any current or history misfires in a misfire data list or any of the live data lists
if you can not get to see a misfire and it has a new cap and rotor and it is not setting a P0300 code try an injector pressure cleaning if it still acts up try a new GM crank sensor if by chance it still acts up then it is either the spider injection or possibly a valve binding in a valve guide which is very time consuming to find which valves are binding
again i am surprised its not triggering a P0300 code these systems will usually pick up a misfire and set a code very quick when misfiring
the problem you have is not being able to test when it is misfiring as the truck needs to be driven down the road and it becomes almost next to impossible to test it when it is acting up
it is just so hard to tell without knowing what cylinder is possibly misfiring
yes if the poppet was restricted or spraying the fuel in a NON mist straight direction due to it being dirty and when it can not mist the fuel raw fuel can not burn as good as atomized misted fuel being sprayed in a nice misting cone pattern out of a fuel injector
yes if it does it in 3rd the transmission is not in lock up so it is not the transmission
a vacuum leak would set codes and case a rough or bad idle and not usually this kind of issue
going over some of my notes lets try 2 simple things
remove the MAF and clean it out good with carb cleaner or MAF spray cleaner if it still acts up unplug the electrical connector to the EGR valve and drive it and see if it still does this
ok clean the MAF if it still acts up then have the injectors pressure cleaned and see if that helps
it works @ 50 % of the time
hi there, New expert here. I am Cam. Have you tried disconnecting the map sensor to see if that makes a change in how it runs? How about the crank sensor wiring, have you inspected that for signs of chafing and such along the side of the block?
OK unplug map and drive it.
Yes if the MAP does not change it, then peel back wiring loom and inspect. Also you replaced the distributor completely? including the cam sensor inside of it?
OK, lets see what the map unplugged does and check that wiring.
Shoot. So then we need to see more live data, what that MAP reading, MAF reading is, Engine coolant temp reading. Intake air temp reading, knock sensor reading to see if any are erratic or out of spec.
If the Mass Air Flow sensor (MAF) was unplugged, did it happen still?
Let me think on this a bit and see.
Ok thanks .COuple questions. First what was the fuel pressure. Second, does the vacuum stay that high when driving and it acts up?
I would please.