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87 Suburban with surging issue

When mine used to do this, it kept throwing the EGR lean burn code, even after i installed a new one, then occasionally a TPS sensor and sa few others, but ultimately it was my fuel pump not pumping enough pressure to do it's job right, not enough fuel. Changed it out and haven't had any issues regarding this since.
 
Same thing happened to me as well like i said above. Maybe soon he will replace the fuel pump and solve his problem. /forums/images/graemlins/ignore.gif
 
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Same thing happened to me as well like i said above. Maybe soon he will replace the fuel pump and solve his problem. /forums/images/graemlins/ignore.gif

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Today, I took a better look at everything, and it seems the distributor was faulty. It had a ton of side play, so I replaced that, and did the cap and rotor again (they were a little fubared) and about 95% of the surging went away.

Tomorrow will be more diagnosing the rest of the problem. It may end up being the fuel pump, or something else fuel related. Hell, at $30 and a couple hour's work, it's probably worth it to do it anyhow. I just hate throwing parts at a vehicle before knowing for sure that it's my problem.

Thanks again for all the info guys, if it seems like I was ignoring the fuel system, I wasn't. I was trying to get as much info as possible before tackling the problem.
 
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You can disconnect the knock sensor and it shouldn't pull any codes.

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Sure it does, it throws a code 42. Happens when you unplug it to set the timing. Timing won't advance if it's unplugged either.
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The kock sensors job is to report any pinging to the ECM so that the ECM can correct ignition timing accordingly. If the knock sensor is disconnected the ECM would never know since it only relies on an electrical signal that is given if there is knocking occurring.

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After some reading, I've found that the opposite is the case. Normally, the sensor sends an 8-10 volt signal to the PCM. When the sensor detects knock, it grounds the signal, sending no voltage to the PCM.
 
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You can disconnect the knock sensor and it shouldn't pull any codes.

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Sure it does, it throws a code 42. Happens when you unplug it to set the timing. Timing won't advance if it's unplugged either.
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The kock sensors job is to report any pinging to the ECM so that the ECM can correct ignition timing accordingly. If the knock sensor is disconnected the ECM would never know since it only relies on an electrical signal that is given if there is knocking occurring.

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After some reading, I've found that the opposite is the case. Normally, the sensor sends an 8-10 volt signal to the PCM. When the sensor detects knock, it grounds the signal, sending no voltage to the PCM.

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The knock sensor WILL NOT pull a code 42, that code is EST (electronic spark timing). The knock sensor also only generates a voltage signal when the engine vibrations or (knock) as we call it are between 6 to 8 Hz. You can disconnect the knock sensor and it WILL NOT bring up any codes. The only time it will bring a code is if the sensor sends a signal to the ECM that is out of its range, or if it keeps trying to retard timing for long periods of time, then it will pull a code 43 for knock sensor signal.
 
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You can disconnect the knock sensor and it WILL NOT bring up any codes.

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Someone with a 1988 truck service manual pull it out and confirm that the below is the same for a truck code 43.

And I quote from the 1988 Camaro Service Manual, VIN "E" (5L TBI):

"To perform this test the ECM will advance the spark when coolant is above 95*C and at a high load condition (near WOT). The ECM then checks the signal at "B7" to see if a knock is detected. The functional test is performed once at startup and if knock is detected when coolant is below 95*C the test has passed and the functional check will not be run. If the functional check fails, the "Service Engine Soon" light willl remain "ON" until ignition is turned "OFF" or until a knock signal is detected.

(B7 is the ESC signal wire to the ECM.)

Not even sure if the TBI trucks use the "external" ESC module like the '88 cars did.
 
I was incorrect about the code, 4X4 HIGH, 43 is for the knock sensor, as you said. 42 is the code that's tripped when you unplug the connector to set base timing. Sorry 'bout that!

However, from the Haynes manual, 67-87 trucks:

"The ESC knock sensor, which is located on the lower right side of the engine block, sends a voltage signal of 8 to 10-volts to the ECM when no spark knock is occuring and the ECM provides normal advance. When the knock sensor detects abnormal vibration (spark knock), the ESC module turns off the circuit to the ECM. The ECM then retards the EST distributor until spark knock is eliminated."

and:

"Failure of the ESC knock sensor signal or loss of ground at the ESC module will cause the signal to the ECM to remain high. This condition will result in the ECM controlling the EST as if no spark knock is occuring. Therefore, no retard will occur and spark knock may become severe under heavy engine load conditions. At this point, the ECM will set a code 43.

Loss of the ESC signal to the ECM will cause the ECM to constantly retard timing. This will result in sluggish performance and cause the ECM to set a Code 43."

That said, I'm not trying to argue, just stating the facts as I read them. Maybe Haynes is incorrect, or later years operated differently, but that's what's in the manual.
 
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You can disconnect the knock sensor and it WILL NOT bring up any codes.

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Someone with a 1988 truck service manual pull it out and confirm that the below is the same for a truck code 43.

And I quote from the 1988 Camaro Service Manual, VIN "E" (5L TBI):

"To perform this test the ECM will advance the spark when coolant is above 95*C and at a high load condition (near WOT). The ECM then checks the signal at "B7" to see if a knock is detected. The functional test is performed once at startup and if knock is detected when coolant is below 95*C the test has passed and the functional check will not be run. If the functional check fails, the "Service Engine Soon" light willl remain "ON" until ignition is turned "OFF" or until a knock signal is detected.

(B7 is the ESC signal wire to the ECM.)

Not even sure if the TBI trucks use the "external" ESC module like the '88 cars did.

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The only manual I have is up to 87 (came with the truck, so it may be applicable to later years as well). It's a Haynes manual, I know it's not the greatest, but here's what it says for 43:

"Check the wires from the ESC module to the ECM. Check the wires from the ESC knock sensor to the ESC module. Check for a loose connection. Replace the knock sensorand/or ESC module."

Kinda leaves you hanging on how to test either of those components though. On my 87, the ESC module is mounted to a bracket on the passenger side valve cover. The same bracket holds the EGR control solenoid as well.
 
Right out of the '88 Camaro manual (again) one of the tests in the flow chart is to tap the block near the knock sensor and watch the scan tool for knock counts.

The rest of the tests require some sort of scanner (GM no doubt) that you can set to "knock" to look for a knock signal, I'm assuming it looks for it on B7. Not sure how it goes about getting that signal though, since the test starts when the engine is idling, (after the functional test I guess, doesn't say, just says engine idling) as I read it, meaning that somehow the GM scanner can induce something that will generate a knock signal to the ECM.

However, tapping the block will prove the knock sensor works or not.
 
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Right out of the '88 Camaro manual (again) one of the tests in the flow chart is to tap the block near the knock sensor and watch the scan tool for knock counts.

The rest of the tests require some sort of scanner (GM no doubt) that you can set to "knock" to look for a knock signal, I'm assuming it looks for it on B7. Not sure how it goes about getting that signal though, since the test starts when the engine is idling, (after the functional test I guess, doesn't say, just says engine idling) as I read it, meaning that somehow the GM scanner can induce something that will generate a knock signal to the ECM.

However, tapping the block will prove the knock sensor works or not.

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I gotta get a scan tool, all I'm doing now is grounding the ALDL. I would think though, that if a signal is sent to the ECM, checking that B7 wire with a voltmeter would tell you the same thing when knocking on the block. No signal, sensor's working. /forums/images/graemlins/thumb.gif

For now though, it's time to enjoy the 4th! Almost beer-30! /forums/images/graemlins/peace.gif
 
In all my years doing diagnostic work I've found one thing to be true, get BACK TO BASICS, plugs, wires, and cap&rotor, then I would definatly spend some time looking at that EGR valve/and solinoid(sp)Is it possible that it's vacumm line is missrouted? Is it's return spring weak, sop the exhaust pressure can push it open? Also clean the throttle bore around the butterfly plates, use carb cleaner and a toothbrush, is thr IAC port plugged or obstructed? it's probably just something stupid /forums/images/graemlins/thinking.gif
 
I agree totally, I think we kind of got off topic going into the theory of operation of the other stuff.

If everything holds true, it will be something totally unrelated to anything we have thought of or talked about. /forums/images/graemlins/smile.gif
 
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If everything holds true, it will be something totally unrelated to anything we have thought of or talked about. /forums/images/graemlins/smile.gif

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We did get waaaay off topic. Ah well, good discussion is always helpful!

Now that it has a new cap, rotor, plugs and wires, I'll be taking off the EGR to clean and/or replace if needed, and check all the lines, etc. It's running a lot better now, I actually towed a car from Long Island to Rhode Island yesterday, and the truck did fine.
 
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