fastpat
Full Access Member
I filled up with 93 octane, alcohol free gas a couple of days ago. Expensive, but worth it in my opinion. 24+ gallons. I need to put preservative in it now.
Getting rid of spark knock
- Thread starter 85lsxMCSS
- Start date
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iamdub
Full Access Member
IAC Code 35: "A shorted ISC control circuit will set a code 35 in the computer's memory. This code can also be triggered on some models by a shorted “nose” switch. A “false” code 35 can sometimes be set by a misadjusted or sticking throttle position sensor (TPS)"
Yup- see if someone monkeyed with the idle screw or otherwise on the TB.
EST Code 42: "
CODE 42 - Electronic Spark Timing or Bypass Fault
Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.
During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.
An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.
The conditions for setting this code are:
- System in BYPASS mode but the ignition module is still controlling timing
- or - - Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.
Typical causes for this code include:
1) BYPASS line is open or grounded
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM"
Well the truck never has stalled out or left me stranded. It just has had a rough idle (down to 300 rpm it so in gear ) and while driving having a spsrk knock that sounded like a machine gun .
I got a new IAC valve and a new ESC module for it . We will check the wiring to make sure it's ran away from the spark plug wires as I read that could be a issue having the plug wires and esc wires too closely ran near each other
Well found out that my blazer doesn't have a ESC module and it's in the ECM. Wasted money buying it.
We checked firing order and that is good. Checking timing again here in a few to make sure it's at 0 TDC. Replaced the IAC valve and idle still is horrible.
Cap and rotor look good as well .
Connections on the ECM looked good .If mine still runs and drives would that eliminate the ecmbeing faulty? If so with not having the module wouldn't that eliminate alot of the ESC module possible faults listed aboge?
We checked firing order and that is good. Checking timing again here in a few to make sure it's at 0 TDC. Replaced the IAC valve and idle still is horrible.
Cap and rotor look good as well .
Connections on the ECM looked good .If mine still runs and drives would that eliminate the ecmbeing faulty? If so with not having the module wouldn't that eliminate alot of the ESC module possible faults listed aboge?
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I would check foran intake manifold gasket leak, they are common on the old tbis. Sounds like you might have a leak which raises the idle rpm and gives the iac code because the engine cant control the rpm so it thinks the iac is faulty.
As for the spark knock, it could be coming from one or more cylinders being lean from the air leak.
If you are at 900 rpm at idl, try unlugging the iac and running it. If its still idling high then you are getting after iac air introduced that is raising the rpms.
When the truck goes into gear, there is an increased demand put on the iac. In the tune it will show i higher duty cycle on the iac. If there is a leak at idle in neautral, the iac might be completely closed trying to bring the idle down, then when you put it in gear, the rpms drop a bunch because the valve is closed, trying to reduce the rpms.
As for the spark knock, it could be coming from one or more cylinders being lean from the air leak.
If you are at 900 rpm at idl, try unlugging the iac and running it. If its still idling high then you are getting after iac air introduced that is raising the rpms.
When the truck goes into gear, there is an increased demand put on the iac. In the tune it will show i higher duty cycle on the iac. If there is a leak at idle in neautral, the iac might be completely closed trying to bring the idle down, then when you put it in gear, the rpms drop a bunch because the valve is closed, trying to reduce the rpms.
Especially check the TBI base gasket for vacuum leak.
I really don't think it's a intake leak. I'll see next time I'm down there and see if I can trace something. I'm going to run some GM top end cleaner flush the system and start over. I just hope it's not wiring. I hate wiring .
So this is not my truck but this is exactly what mines doing .doesn't make sense noise til you do a quick rev or constant cruising it sounds like a1930s gangster shooting a machine gun.
I was told maybe if the distributor has some play it could throw things out of wack .I also haven't replaced the following yet
Distributor cap and rotor
Ignition module
I was told maybe if the distributor has some play it could throw things out of wack .I also haven't replaced the following yet
Distributor cap and rotor
Ignition module
bigfootchiro
Full Access Member
Sounds exactly what my Hoe is doing, but haven’t had time to fix it lately. Could be a rod bearing. That’s what I’m checking next
