I have a 1989 chev c3500 with a 454 tbi vin code n I am getting a knock singnal on my 4000e scanner and the timing is being retarded the full 20 degrees, their is no knock sensor or esc module or wiring on the truck any ideas?
snipped-for-privacy@new.rr.com
Is it carbeurated? If it is TBI like you say, you do have a KS, ESC and wiring.
Doc
no ks,esc or wiring. snipped-for-privacy@new.rr.com
Ok I need some history here. Did you just buy this truck? Was it running fine up until a few days back? Fill me in. If the ECM doesn't get a signal from the knock sensor (routed thru the ESC) it will retard the full amount to prevent engine damage as it no longer has the ability to control advance for spark knock.
Details, details, details, I need details.
Doc
This truck was purchased with a bad engine all intake pushrods were bent and acouple of valves
rebuilt same engine and put back in
their is no wire coming from the ecm for an esc module.
message
cant always trust the scan tools...Are you just trying to find something wrong with the truck? Did you check it with a timing light to see what is going on with the timing? I would bet a small amount of money that if you checked it with the light you would see it isnt really retarding it like you think. Seems kinda funny that the truck doesnt even have a knock sensor and your scan tool says it's knocking? Anyway, just some things to think about and check. GL
yes it is running wired checked timing with light and its being retarded 20 deg, when at operating temp. in gear the idle increases and engine will start to race when at stop, really bad when in neutral.
according to the Mitchell wiring diag. the 7.4l didn't use knock sensor or esc mod.
It seams you are barking up the wrong tree (timing) to me. It is usually a mistake to jump all over the computer first. Its been a while but I'm remembering something about scan tools screwing with timing . Does that scanner have a "road test" mode? It probably doesnt. Does it do the same thing without the scanner hooked up? You really should check out things like vacuum leaks, you know-basic stuff first especially since you dont even have a check engine light I assume? Check the base timing for sure, (since you had the dist out), ask "Doc" how to set it on that model. (Probably disconnect the four wire on the dist, I dont remember for sure on that year.)If it still has the sticker under the hood it will tell you. Then check for anything easy and basic like vacuum leaks, egr stuck open, vacuum hoses routed wrong/not connected. Also use that scanner to look at the idle control to see if the computer is trying to make it idle right. Im not positive on that year, or your scanner, but you should be able to see IAC postion. If it shows the computer trying to jack up the idle or slow it down but it aint happening could just be the IAC sticking/bad. Just for fun check the advance *without* the scanner on it. Im curious about the diff with and without it. Did you drive it and give it a chance to learn and get its idle straight? Did you mess with the minimum idle? (the idle stop screw on the TBI, I hope not :) ) GL
doesn't matter with or with out scanner hooked up does the same thing,
checked vac. 16in of vac in park in gear drops assuming because of the timing be so far out of whack
message
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.