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91 suburban est code trouble

M

Mountain_man

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Aug 20, 2007
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Globe, AZ
Ok I have been having timing problems with my 350. I set the timing at 0 in closed loop with est wire unplugged. Shut down the engine and reconnect the plug (wire right next to brake booster) and restart the engine. The code will not clear. I've pulled the fuse and everything. I recheck the timing with the wire plugged in and it still shows same 0 timing! I've verified through this site that it's the correct wire to unplug yet the light keeps coming on with same code. I've also got a serious knock in the engine with the timing set this way. What else could I be looking at?
I'm getting code 42 btw.

I also just changed to the 3wire o2 sensor and it's working correctly. Has got to be a problem with computer seeing the advance from distributor once connected. Would really explain everything but I'm going crazy here.

I've done no real changes since this started happening however new cap/rotor/wires/plugs and I've verified the wire placement to be correct. I hope someone can help with this cause it's not drivable. Thanks
Josh
 
Well I have a new distributor on the way. From what I can see from all this information around ck5 the pickup coil could be the problem. I noticed quite a bit of shaft play so I'm hopeful. Any other ideas? Thanks.
 
Are you pulling the right fuse to reset the ECM? There are 2 of them. Marked ECMa ECMB or 1 or 2. I cant rember which one to pull. Might want to pull them both to make sure you got the right one.
either that or disconnect the battery for 5 minutes or so.
Code 42 will be set when the timing bypass wire is disconnnected. Sometimes you have to completely reset the ECM to get it to clear, and get the ECM to control the timing right.
With the bypass wire connected you should usually be running 16-20 degrees timing at idle.
 
Their is ECM A and B and I've tried both. usually just A used to work. I've plugged in the wire and unplugged and both shows the same timing mark. Doesn't move like it's supposed to. I'm so boggled.
 
Ok well I replaced the distributor with a brand new one and still no go. It worked perfect and functioned as it should for 3 or 4 restarts. Once I started it to take for a test drive that code came right back and it stopped advancing the timing again!

I really hope someone can help me with this as it's driving me crazy. It's also my primary transportation.

Josh
 
After you replaced the dist, have you checked trouble codes? Are you getting a code 12 at the begining of the trouble code check? Does your check engine light lite up when you turn the key on with out starting the engine,
 
Yes the check engine light is on when I turn key on and when I start. If I let it sit a sec it turns on about 2 seconds after starting it. Time to start replacing wiring. Guess that's the only other place to go without replacing things at random.
 
You may have some issues with the knock sensor circuit, it'll set code 42 if it is not functioning properly... The knock modules are pretty robust, but it is easy for the sensor in the block to fail. Check it's wiring is good before you replace anything though.
 
Ok if the knock sensor wire is touching the header and let's say grounding will that actually do anything? or will it just cause a corrupt reading of the knocks? I'm wondering cause the knock sensor is a peizo crystal so it creates the energy to travel right? Just trying to track this down it has gotten worse.
 
If the knock sensor wire is grounded, then you will set Codes 42 and 43. 42 is a general timing system failure, 43 is a knock sensor failure (shorted / non existent).

The knock sensor should always be producing some voltage due to the natural vibrations of the block, but will produce way more voltage when the engine is pinging. Having that wire grounded, or open, will cause the timing system to fail to operate properly. The ECM does a knock sensor test by advancing the timing enough to make the engine ping, then backs off. If that test fails, the ECM will not dynamically time the engine, but will simply follow pre-programmed tables which are very conservative to say the least.
 
Ok! I found a few wires coming off the starter that were also touching bare wire. I've adjusted and repaired the wires. It runs great except once it goes into closed loop (datamaster) it begins knocking a ton. I'm guessing this is a timing issue however it's set at 2 adv. and still doing this. Can the distributor I had in the vehicle have jumped a tooth and caused this to happen? I tried 0 timing and it seems to be the same as well.

I'm slowly tracking this down but could sure use some help or at least ideas.
 
What does the ECM set the timing to when it goes into closed loop and the engine begins to knock? What is your oil pressure like?

Does the engine have any kind of a tick or light bearing knock when it is running in open loop?
 
Timing sits at 16.9 or 17 on timing in closed loop through ecm readings. Oil pressure is good sits around 30ish on gauge. No noticable knock or anything in openloop perhaps a little tick? Hard to hear with the exhaust on there. Very few knock counts in open loop though.
 
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