Took out a fuse in my 1991 Chev 3/4 ton 2 wheel drive ...

It seems that fuse is a gauge/idle fuse.Here is the wire diagram for your truck to help you trace any shorts.What was the fuse you incorrectly removed and replaced?I don't see where you could have done anything to cause the problem by switching fuse unless the truck was running or key on while you were doing that.I would inspect the fuse panel very closely on the back side.Here's the schematic. Images available only to Customers.

Edited by railman on October 16 2005 at 1:21am

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The fuse I took out was the ignition fuse and the truck was running and the truck died. I put it back in and I started the truck. That is when I noticed the tacometer bouncing iradicaly and that is when the check engine light came on. The engine was running real rough like it was missing. What did I do and how do I fix it.

The fuse I took out was the ignition fuse and the truck was running and the truck died. I put it back in and I started the truck. That is when I noticed the tacometer bouncing iradicaly and that is when the check engine light came on. The engine was running real rough like it was missing. What did I do and how do I fix it.

AHHHH,You did not mention the CEL was on before.The place to start is by retrieving the codes that the ECM has stored.I will show you how to get the codes and then you should post back with that info.I should be around most of today to guide you.Here are the procedures for code retieval on your truck.

Also post back with your transmission model e.g.,4L60-4L80

1988-95 MODELS

See Figures 1 and 2

Listings of the trouble for the various engine control system covered here are located in this section. Remember that a code only points to the faulty circuit NOT necessarily to a faulty component. Loose, damaged or corroded connections may contribute to a fault code on a circuit when the sensor or component is operating properly. Be sure that the components are faulty before replacing them, especially the expensive ones.

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Fig. 1: ALDL connector-1988-92 models

The Assembly Line Diagnostic Link (ALDL) connector or Data Link Connector (DLC) may be located under the dash and sometimes covered with a plastic cover labeled DIAGNOSTIC CONNECTOR.

1. The diagnostic trouble codes can be read by grounding test terminal B. The terminal is most easily grounded by connecting it to terminal A (internal ECM ground). This is the terminal to the right of terminal B on the top row of the ALDL connector.

2. Once the terminals have been connected, the ignition switch must be moved to the ON position with the engine not running.

3. The Service Engine Soon or Check Engine light should be flashing. If it isn't, turn the ignition OFF and remove the jumper wire. Turn the ignition ON and confirm that light is now on. If it is not, replace the bulb and try again. If the bulb still will not light, or if it does not flash with the test terminal grounded, the system should be diagnosed by an experienced driveability technician. If the light is OK, proceed as follows.

4. The code(s) stored in memory may be read through counting the flashes of the dashboard warning lamp. The dash warning lamp should begin to flash Code 12. The code will display as one flash, a pause and two flashes. Code 12 is not a fault code. It is used as a system acknowledgment or handshake code; its presence indicates that the ECM can communicate as requested. Code 12 is used to begin every diagnostic sequence. Some vehicles also use Code 12 after all diagnostic codes have been sent.

Edited by railman on October 16 2005 at 11:54am

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Hello, we jumpered a and b on the aldl and checked for code 12 and it flashed the 1 short, then 2 short as you said.

Also the tranny had 17 bolts and the label stamp on the passengers side read:

hydromatic
BA    P
serial    model      
91        163

We need to know what direction to go now.

Thanks.

You must leave it jumped and watch for the codes after code 12.The 12 is just telling you that the cycle has started.You need to keep watching for the codes that follow 12.When the cycle finishes code 12 will blink again.

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Ok, how long will the time be between the code given and the 12 code. It appeared to continue flashing the 12 code. Also, do I keep the A and B positions jumpered?

Thanks.

Yes keep it jumped.The codes should follow in a couple seconds if there are any.If you disconnected the battery there won't be any codes just 12.Or if there are no other codes it will just flash 12.If you disconnected the battery or otherwise erased the codes.Remove the jumper-start and run the truck until the Engine light lights and re test for codes.I'm guessing you may have spiked the EGR solenoid when changing the fuse but want to confirm it with the code.You can unplug the EGR solenoid or just the vacuum hose at the valve and tell mif it smooths right out too.

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Thanks, we did remove the battery post trying to reset something hopefully. My dad just went to Autozone and they tested it there and got a 68 code. Please reply asap as Autozone closes in 5 minutes.

Thanks.

code 68 is a Transmission overdrive code which shouldn't be affecting here.Better read again.long flash is tens and short flash is ones so 3long flash and 4 short flash is code 34.

Did you unplug the EGR valve as I suggested?

Edited by railman on October 16 2005 at 6:18pm

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Well, Autozone concurred with what you said, no 68 code in their book either. My dad said that it was 6 flashes and then 8 flashes over and over. He said that they all appeared short. Also, Autozone is open for another hour and a half, my mistake. Is there a possibility that there is a 68 code readable by the dealership or that it was 6 and 8 error codes(not listed on the other sheet you sent)?

Thanks.

sorry, they did unplug the egr valve and it ran the same.

Thanks.

Did you read my posts above ???68 is overdrive code.Not at issue here.Unplug the Vacuum hose at the EGR Valve,back right rear of engine behind air filter.Plug the vac hose.Does it smooth out?

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Ok, yes, they removed the hose and plugged back in. No change. I missed the 68 code post cause I was in a hurry. Well, now the truck is running very rough and doesn't want to idle. Aslo is smoking, white. They are suggesting fuel problems at Autozone. Any other suggestions?

Thanks.

the only other thing I can see is the possibility that the injector drivers in the ECM were damaged.You can look into the throttle body at the injectors to see if BOTH are squirting.If not the circuit can be checked with a noid light.Don't give up so easy.Your almost there.

Edited by railman on October 16 2005 at 6:53pm

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Ok, they said that both injectors are squirting and that they are probably going to take it to a shop. Thanks again and I will send you another payment for your speedy service. They may post again, but thanks for everything in case they don't.

Thanks. Todd

OK.You don't have to click ACCEPT all the time.Let me know how it goes by sending me a PM.Remember the injectors have to pulse and not pour into the throttle body.You may be able to just tap on the ECM behind the glove compartment if one or both is stuck on which would cause a flooding condition.I know you don't have a noid light to see if they are stuck on but you can see by the way the fuel comes out.It should be pulsing.You could also unplug one or the other running and see if it smooths out.

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Sorry, what do you want me to unplug? I will try that, need a little more specifics. I do belive it is flooding and my dad said that it wasn't pulsing, but seemed to be pouring the fuel into the carb.

Thanks. Todd

A guy that was at Autozone said that it might be the pickup coil in the distributor because the tach. was bouncing all over the place. Could this be related and or another simultaneous problem?

Thanks, Todd

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Ok, sorry about the o/p. I checked the codes again, because the truck wasn't here before and now is. They only mentioned the 68 code, but I'm now getting a 22 and 45 code also. I still have to check the ECM with the test light. (I will do so shortly) I will post back and then you can reply after that. I appreciate you help.

Thanks. Todd

Ok, I checked the injector leads and they are pulsing like you mentioned. I then tried unplugging the Electronic spark timing module, with no change. I was lead to believe by a local mechanic that the ignition coil might be the problem. Could that also cause the erratic tach. problem and is there any tell tail signs or just try replacing the ignition coil?

Very possible.Here is how to isolate bad ignition coil or Pick up coil.

Fuel Injected Engines

See Figure 1

1. Tag and disconnect the distributor lead and wiring from the coil.

2. Connect an ohmmeter as shown in Step 1 of the accompanying illustration. Place the ohmmeter on the high scale. The reading should be infinite.

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Fig. 1: Fuel injected engine ignition coil test

3. Connect an ohmmeter as shown in Step 2 of the same illustration. Place the ohmmeter on the low scale. The reading should be very low or zero. If not replace the coil.

4. Connect an ohmmeter as shown in Step 3 of the same illustration. Place the ohmmeter on the high scale. The meter should not read infinite. If it does replace the coil.

5. Connect the distributor lead and wiring.

PICK-UP COIL

See Figures 2, 3 and 4

1. To test the pick-up coil, first disconnect the white and green module leads. Set the ohmmeter on the high scale and connect it between a ground and either the white or green lead. Any resistance measurement less than infinity requires replacement of the pick-up coil.

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Fig. 2: The pick-up coil is located inside the distributor

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Fig. 3: Testing the pick-up coil-coil-in-cap

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Fig. 4: Testing the pick-up coil-separate coil

2. Pick-up coil continuity is tested by connecting the ohmmeter (on low range) between the white and green leads. Normal resistance is between 500 and 1500 ohms. Move the vacuum advance arm while performing this test. This will detect any break in coil continuity. Such a condition can cause intermittent misfiring. Replace the pick-up coil if the reading is outside the specified limits.

3. If no defects have been found at this time, and you still have a problem, then the module will have to be checked. If you do not have access to a module tester, the only possible alternative is a substitution test. If the module fails the substitution test, replace it.

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Edited by railman on October 17 2005 at 8:34pm

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"It is much wiser and cost efficient to ask a question than to stumble blindly through your auto repairs".Please Click Accept if my answer was helpful.

Will check the p/u coil as you wrote, but I have another problem. I went to change the distrib. cap and rotor and labeled the wires but didn't mark pos. 1 on the distrib. cap. Please help!! I hope I hear back tonight, but if not, thanks again for all your help, you're good!

Thanks, Todd