Need help with pickup
07-04-2013, 09:57 AM
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Need help with pickup
Ok I have been pulling my hair out on this one. 1992 pickup 3.0. Truck was overrevved and the fan came apart. I replaced all damaged parts. Fan, dust cap and rotor, battery and repaired washer tank wiring. The vehicle will start run for a 10-20 sec then die. I have also swapped Maf, dist, coil, igniter, ECM with known good truck and no difference. So if I unplug the Maf and jump the fuel pump wires the truck will start and run great. If I plug the Maf back in it will not run. What could be causing it to shut down when the Maf is plugged in? I have also tried unplugging the coolant temp sensor, and tps. Btw this is not a ca truck.
07-04-2013, 11:58 AM
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The Circuit Opening Relay is actually two relays in one. One coil closes the contacts when it receives a start signal, the other coil keeps the contacts closed when it receives a signal from the Volume Airflow Meter.
I believe you said your replaced the VAF with a known good one and you still have the same problem. I would now suspect either the COR (possible bad coil that receives signal from VAF), or bad wiring between the COR and VAF.
Referencing the diagram in the link below, you can see that either a bad coil in the COR, or an open in the wire labeled "FC" will cause your vehicle to start, then shortly stall. It is likely that when your fan went, it severed the wire that connects the COR to the VAF. This wire is green with a yellow stripe. You could check for continuity in that wire from the COR to the VAF connector. Also check that wire labeled "E1" on the VAF connector has continuity to ground (this wire is brown). If this wire is severed, it would also prevent the circuit from operating.
http://personal.utulsa.edu/~nathan-b...87fuelpump.pdf
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I believe you said your replaced the VAF with a known good one and you still have the same problem. I would now suspect either the COR (possible bad coil that receives signal from VAF), or bad wiring between the COR and VAF.
Referencing the diagram in the link below, you can see that either a bad coil in the COR, or an open in the wire labeled "FC" will cause your vehicle to start, then shortly stall. It is likely that when your fan went, it severed the wire that connects the COR to the VAF. This wire is green with a yellow stripe. You could check for continuity in that wire from the COR to the VAF connector. Also check that wire labeled "E1" on the VAF connector has continuity to ground (this wire is brown). If this wire is severed, it would also prevent the circuit from operating.
http://personal.utulsa.edu/~nathan-b...87fuelpump.pdf
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Last edited by rustypigeon; 07-04-2013 at 12:19 PM.
07-04-2013, 01:00 PM
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rustypigeon is correct (and a good explanation, to boot).
But I don't have a lot of faith in "known good" parts removed from some other truck, so I would check that too. http://personal.utulsa.edu/~nathan-b...92volumeai.pdf (Note that the manual shows a different pin-out for 22re -- come to think of it, where did that "known good" VAF come from?)
But I don't have a lot of faith in "known good" parts removed from some other truck, so I would check that too. http://personal.utulsa.edu/~nathan-b...92volumeai.pdf (Note that the manual shows a different pin-out for 22re -- come to think of it, where did that "known good" VAF come from?)
07-04-2013, 02:16 PM
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Swapping parts at random is the slowest, least productive way to find an electrical problem. As rustypigeon suggested, you're most likely to have broken a wire in the engine compartment with all the wreckage flying around. The relay itself could be the problem, but not likely. But it is easy to tell.
Just so you know.
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07-05-2013, 08:01 PM
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You need to invest in a low cost but decent MULTIMETER. Electrical problems will kick your butt every time without them.
Please don't go buy some giant pile of crap from whatever random hardware store is near you either. You can't trust them, and if you can't trust a meter then why even have one?
The explanation given here, that the 2nd coil in the COR isn't getting energized, seems mostly likely. That coil is only driven by the fuel pump switch in the VAFM. This simple sequence of operations will give you a pass/fail of that component:
1. Jump +B to FP through the diag connector (or whatever method you're already using to do this).
2. Start the truck, wait 20 seconds because that's how long it would normally take to die.
3. AT THE VAFM, disconnect the cable and measure continuity from pins FC to E1 on the VAFM itself. The FSM article on the VAFM gives you the pinout of the connector. Your meter should beep (remember to put it in continuity mode). If this doesn't happen, VAFM is bad.
4. AT THE COR, measure voltage from FC to E1. It should read B+ volts, 13-15 volts. Plug the VAFM connector back in, measure across the same pins. It should read around 0V. If it doesn't, you have bad wiring.
Two simple measurements diagnose this component and you don't have to rewire anything. Saves massive time and money.
Please don't go buy some giant pile of crap from whatever random hardware store is near you either. You can't trust them, and if you can't trust a meter then why even have one?
The explanation given here, that the 2nd coil in the COR isn't getting energized, seems mostly likely. That coil is only driven by the fuel pump switch in the VAFM. This simple sequence of operations will give you a pass/fail of that component:
1. Jump +B to FP through the diag connector (or whatever method you're already using to do this).
2. Start the truck, wait 20 seconds because that's how long it would normally take to die.
3. AT THE VAFM, disconnect the cable and measure continuity from pins FC to E1 on the VAFM itself. The FSM article on the VAFM gives you the pinout of the connector. Your meter should beep (remember to put it in continuity mode). If this doesn't happen, VAFM is bad.
4. AT THE COR, measure voltage from FC to E1. It should read B+ volts, 13-15 volts. Plug the VAFM connector back in, measure across the same pins. It should read around 0V. If it doesn't, you have bad wiring.
Two simple measurements diagnose this component and you don't have to rewire anything. Saves massive time and money.
07-05-2013, 08:30 PM
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Did the fan damage the part of the SRS that is mounted to the lower left of the airfilter?
If this part is leaking it will prevent the AFM from getting full draw and cause low idle or even the FP to no stay on.
Also scary is if any plastic peaces loose in the air intake area.
If this part is leaking it will prevent the AFM from getting full draw and cause low idle or even the FP to no stay on.
Also scary is if any plastic peaces loose in the air intake area.
07-05-2013, 09:00 PM
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Maybe I'm not understanding it or you guys are not. If i the jump the fuel pump switch at the Maf the engine starts and runs as long as the Maf is unplugged. I have cut the two fuel pump wires off the Maf for testing. They are jumped together now. If I disconnect the green and black wire the truck will run. This wire runs to the ECM and tps according to my info. I have ran a new wire from the Maf to the ECM replacing the green with black wire.
07-05-2013, 09:40 PM
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Based on your careful diagnostics, I think we're 99% sure that your COR is not closing when there is air flow through the VAF. You say that the engine runs if you "jump the fuel pump switch at the Maf ... [with] the Maf unplugged." I assume that means you connect pin 1 (FC) to pin 2 (E2) on the engine-side of the VAF connector.
Doesn't that tell you that the reed switch inside the VAF is not closing when the vane moves? Why don't you pull the connector from the VAF, put your ohmmeter on pins 1/2 of the VAF, and see what happens when you push the vane with your finger. If it doesn't go from open to short as soon as the vane moves, there's your problem.
For what it's worth, my schematics show FC as Green-Yellow, and E2 as Brown. But I have very little faith in wire color from schematics. If that's an issue, you already understand the circuitry well enough that you could trace out each wire with your meter.
Doesn't that tell you that the reed switch inside the VAF is not closing when the vane moves? Why don't you pull the connector from the VAF, put your ohmmeter on pins 1/2 of the VAF, and see what happens when you push the vane with your finger. If it doesn't go from open to short as soon as the vane moves, there's your problem.
For what it's worth, my schematics show FC as Green-Yellow, and E2 as Brown. But I have very little faith in wire color from schematics. If that's an issue, you already understand the circuitry well enough that you could trace out each wire with your meter.
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