understanding what the engine is doing.

[drewkimble48]

Hey there!
So I have begun using Tunerpro RT to diagnose my completely stock 93 gmc c1500 350 4l60e and figure out why I am getting a rough idle in gear and after checking vacuum, it intermittently drops 1-2" when the rpms drop.
I understand what like the sensors should be (except the map sensor because I thought if it has 18" in vacuum, it would have about 60 kpa which it registers around 30 to 40 at idle. also I just checked to see if it held a vacuum and it did).
Anyways, is there anything that i should look at closely when the engine hesitates on the datalog and explain to me what the engine should do to run perfectly via the engine senors, blm , intergrator so on and so forth.
looking at all these inputs the ecu is giving me is all new and alittle more complicated since I am so used to using carburetors.
thanks guys

[dave w]

Maybe you can post a data log (.xdl) file. Please attach the .adx you used to record the data log.

dave w

[drewkimble48]

Hey Dave, I'm actually glad that you replied back to this thread. You posted up some spread sheets of my engine about a week ago under the GM EFI SYSTEMS part of the forum under "tunerpro up and running. time to decipher my readings."

I am still kind of lost as to what's going on exactly. I have been looking at them for some time and I'm still kind of lost as to what I am seeing. If I am reading them right though, it appears I am running rich at idle. Haven't been sure though with the numbers running at around 110-125. also the knock counts is still puzzling me to.

[dave w]

BLM numbers below 128 are rich. BLM numbers above 128 are lean. The acceptable range rich / lean is +/- 5, so BLM's above 123 and below 133 are acceptable. Add or subtract fuel in the VE table to correct rich / lean.

Knock is common, excessive knock is a problem. Knock counts of 10 or less are usually not a problem. Knock counts over 50 is a serious problem. Usually subtracting 1 ~ 3 degrees in the spark table will reduce knock. Sometimes there are mechanical problems causing excessive knock, like aftermarket lifters, aftermarket rocker arms, loose bolts on the torque converter and list goes on.

dave w

[dave w]

I've attached a Tech Library document (.pdf) that has tuning information. Most of the "Theory of Tuning" applies to factory computers.

dave w

[drewkimble48]

looking at your spread sheet on knock counts v. map v. rpm, I don't have knock counts in every cell but the very few cells that do, I am seeing upwards to 40 knock counts sometimes. This may be a dumb question but, the way I see it, I have something knocking internally, would you say I should take those readings into consideration that my engine is finally going out or that I'm overlooking it?
I mean it does have 319,000 miles on it now and I have never dropped the pan , change head gaskets nor pulled the motor. It just blows my mind that the truck starts up and runs fine up until it warms up, then it develops the distinct-able miss while I am at a stop light idling.

[dave w]

I'm thinking some of the knock counts you are seeing are from worn valve train parts, (cam, lifters, rocker arms & valve springs). It's common for a ultra high mileage SBC's engines to have worn camshaft lobes possibly causing a miss.

dave w

[drewkimble48]

Yeah that's what I have been speculating a lot since last week. Might as well get a new long block and swap it out. Why spend more money to fix it for a while only to pull the engine for worn rings eventually plus if I am to get a new job in Florida, better have a good engine before I get there and not have anywhere to work on it.