1990 Suburban (350 TBI) knock problem

[TheApocalyptican]

I've had a pretty consistent problem with my Suburban since I bought it. But it seems to be getting worse. I have a problem with a bogging at lower rpms that is inconsistent. I have finally tracked it down to the timing. The computer is retarding the timing due to knock counts. Knock counts seem kinda high to me in winaldl, but don't know what "normal" is considered to be. According to the datalogs blm's, I have issues at low rpm with running rich. I thought lean is what caused knocks though? I "think" it is actually pinging, and not something else making a similar noise. Problem is, for the most part, whatever is making the noise is very faint, and thus hard to tell what it is.

I have doubts about the EGR valve as when I hooked up a vac source to it, the engine didn't seem to be effected. Thought I checked the map sensor, but am going to test it again. The tps tests as good. Don't know the fuel pressure, but I have a new delco fuel pump, new filter, and rebuilt tbi (including new fpr spring). Almost positive the exhaust isn't restricted at all. Cap, rotor, wires, and oe plugs are all fairly new. O2 sensor is fairly new as well, but only problem might be that it's a bosch.

Tried to give as much info as I could. Ideas?


Mods: I realize you moved this to the "correct" forum, but I posted it purposefully in the 88-98 section due to more people there having TBI's and experience fixing them.

[scotts62]

The cool temp sensor give these things fits too, they are pretty cheap just to throw one in and see if it helps.

[TheApocalyptican]

Originally Posted by scotts62

The cool temp sensor give these things fits too, they are pretty cheap just to throw one in and see if it helps.

I knew I would forgot to mention something that has been replaced....CTS was changed out just after I bought it. It ran eye wateringly rich at the time.

[Jonboy]

Make sure that the distributor is clocked correctly. I was having similar problems, and it ended up being the distributor clocking. The plugs on the side should be pointing at about 2 o'clock. Disconnect the SPOUT connector, and set initial timing at about 2 degrees advanced. See what that does.

[TheApocalyptican]

Originally Posted by Jonboy

Make sure that the distributor is clocked correctly. I was having similar problems, and it ended up being the distributor clocking. The plugs on the side should be pointing at about 2 o'clock. Disconnect the SPOUT connector, and set initial timing at about 2 degrees advanced. See what that does.

The plugs are at like 1 or 2. I had the timing set at 2, but it "knocks" less at 0. So right now it's at 0. Pretty sure something is funny with the MAP sensor, so I'm going to replace that, and go from there.

[MudDiGGer25]

I really didnt want to resurrect a really old thread but after weeks of google searching im coming up with nothing definitive, I must. I can describe my engine almost EXACTLY the same, all the same parts and more replaced, high knock counts when i rev it and around cruising speeds in town. I unplugged my knock sensor and the "bog" went away but so did alot of my power. fuel type used barely affects it. (87,88,89,91,93, with or without ethanol) my next thing is to double check my FP then replace the knock sensor. but there are so many threads like this one that never got a result posted, and that is frustrating lol

[Front Range]

This might help.

CODE 43

Trouble Code 43 indicates that there may be a malfunction in the Electronic Spark Control (ESC) circuit. ESC is used to sense spark knock (pinging) and retard the timing to eliminate it. The knock sensor is located at the rear of the engine block. The ECM will retard the timing by as much as 20 degrees in 1 degree increments. A loss of knock sensor signal or loss of ground at the ESC module will cause the signal at the ECM to remain high. The ECM will act as if no knock is present, and may possibly result in engine damage, due to detonation.

Code 43 is set when:
1. Voltage at Knock Sensor is above 4.8 volts or below .64 volts.
2. Either condition is met for about 10 seconds.

Possible causes:
1. Open or shorted knock sensor
2. Loose knock sensor
3. Excessive mechanical noise within engine
4. Improper or incorrectly installed MEM-CAL in the ECM or defective ECM
5. Intermittent open in the EST line to the ignition module

[MudDiGGer25]

Thanks forreplying. However shortly after i ressurected this thread i was doing some reasearch into the BLM & INT readings and noticed even though the cts. Is reading up to 208F it jas never entered.closed loop. And i am suspecting my minimal 02 reading are to blame, either its faulty or its too downstream. Thsnks, and sorry for resurrecting a dead thread.

[MudDiGGer25]

Just wanted to post my results even if this is an old thread, just in case it helps some one out down the road.

Here is a video of the data readouts this afternoon. I did let it warm up to the point where the needle just raised off the line on the gauge.

https://www.youtube.com/watch?v=IZn_...r#action=share

I still have some knock counts when i rev it quick but only then.

MY o2 seems to be operating properly even without the heater element hooked up yet. I was in closed loop already when I connected the scanner.

I have noticed more kick on the 1-2 shift at WOT anywhere from 3000-6000 (if i control it manually)