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Runs perfect!!.....heat soak.....wonít stay running

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Runs perfect!!.....heat soak.....wonít stay running

Old 10-31-2018, 04:26 AM
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Heat soak!! Wonít start after sitting for 20 minutes!!

ďThrewĒ at truck so far coolant temp sensor and FPR. last 3 episodes. First: warmest day of the fall about a month ago it dies driving around town. Would start every time and just bog to a stal. 2nd. Had it idling for about 10 min on a cold day picking my daughter up from school. Got out for about 10min and then it did the same thing. 3rd: yesterday it got to 60 and sat in my driveway for a couple hours. Did the same thing. Last night I attempted duplicating scenario after doing some research by letting it idle for a while. Went back to start and it did it. Jumped fuel pump and it runs. Truck runs perfect when it wants to run. Before it was doing this heat soak in the summer only when it got to like 80 or warmer. And when it did it then it wouldnít even start up. It would just crank. I tried unplugging AFM and running on limp like ppl do but it didnít work for me. The truck still didnít start. The heat soak is getting worse. Last night I ohmed out the AFM and everything read fine. Either tonight or close to it I am going to check the OCR. From the signs of it. It has to be heat soak related so Iím saying something under the hood. How do I check the AFM fuel switch by itself. Iím thinking I have to duplicate the problem again and do my tests. I canít see the OCR getting heat soaked? Any ideas?

Last edited by bensyota; 01-17-2019 at 04:43 PM. Reason: Diangnosing issue further
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Old 11-02-2018, 03:45 PM
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So I got to the OCR and did the ohm test. With no power supplied. First reading is coming out 27 and some change. Second reading is coming out 136 and some change. Does 2 ohms over make a difference? I mean Iím out of the specified range. Can anybody chime in on this please? And thank you
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Old 11-03-2018, 09:07 AM
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Okay so I just did the 2 voltage applied tests to the relay. It tested good. I also did the solenoid unplugged and tested hearing the click of the relay. It clicked every time I turned the key to start. Showing pump is getting voltage for initial start. But when I fully open the flap on the AFM with the key to ON, I canít hear the relay click at all. But how is that possible if I can instantly plug the solenoid back in, start the truck and it runs fine? Iím getting full voltage to pump as well. I was hoping this is where something would pop up and make my troubles easy haha. Should I try duplicating the problem again and then test. But my question is still with the above mystery for now. Again! Can anybody chime in please
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Old 11-03-2018, 09:34 AM
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Intermittent issues are hard to track down at the best of times (when the issue is showing up), and some times almost impossible at the worst of times (when they aren't manifesting). You will need to repeat the testing until you get a consistent answer "this part is bad". There are several parts under the hood that are susceptible to heat problems mostly along the ignition system, but all electrical connections also can act up if they are loose/wet due to heat or vibration.

There is no such thing as a limp mode for the VAFM, you are confusing this with the TPS (throttle sensor).
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Old 11-03-2018, 09:44 AM
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Originally Posted by bensyota View Post
So I got to the OCR and did the ohm test. With no power supplied. First reading is coming out 27 and some change. Second reading is coming out 136 and some change. Does 2 ohms over make a difference? I mean Iím out of the specified range. Can anybody chime in on this please? And thank you
Optical Character Recognition? I'm going out on a limb here, and guessing you're working on the Circuit Opening Relay. Do you think that every person who might read your post has memorized the entire FSM, and knows what the "ohm test" is? Okay, I took the time to look up the manual on the COR http://web.archive.org/web/201003261...96circuito.pdf , and I don't see any test that involves an ohm reading. So I can't figure out what you are doing.

Originally Posted by bensyota View Post
Okay so I just did the 2 voltage applied tests to the relay. It tested good. I also did the solenoid unplugged and tested hearing the click of the relay. It clicked every time I turned the key to start. Showing pump is getting voltage for initial start. But when I fully open the flap on the AFM with the key to ON, I canít hear the relay click at all. But how is that possible if I can instantly plug the solenoid back in, start the truck and it runs fine? Iím getting full voltage to pump as well. I was hoping this is where something would pop up and make my troubles easy haha. Should I try duplicating the problem again and then test. But my question is still with the above mystery for now. Again! Can anybody chime in please
I assume "solenoid" refers to the starter solenoid, and you're unplugging it so you can hear the COR when you turn the key to STArt. If not, I don't know. From your description, it sounds like you have an intermittent problem, that may (but I'm thinking not) have something to do with heat-soak. My guess is a loose connection somewhere, possibly in the VAF-COR circuit.

To see if you're looking at the correct circuit, always carry your multimeter and a paper clip. If the truck dies, leave the key on and test for voltage on B+ to ground (diagnostic connector). If you have battery voltage (about 12.6v), use the paper clip to jumper B+ to FP. This bypasses the COR-VAF circuit and should force the fuel pump to run. If the truck starts, you've narrowed down the problem. If it still doesn't, it must be somewhere else.
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Old 11-03-2018, 10:05 AM
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Originally Posted by bensyota View Post
So I got to the OCR and did the ohm test. With no power supplied. First reading is coming out 27 and some change. Second reading is coming out 136 and some change. Does 2 ohms over make a difference? I mean Iím out of the specified range. Can anybody chime in on this please? And thank you
There are nearly 1.5 thousand pages in the service manual. You should not expect us to recall all of the specifications. Always try to include what the book says you should have for test results, at least provide a section and page number for the test you have undertaken.




So you have out of spec resistance between STA and E1. This means the COR won't be getting the current it needs/expects to close the contacts when the key is in the STArt position.

You have out of spec resistance between B+ and FC. This means the COR won't be getting the current it needs/expects to close the contacts when the VAFM switch is in the closed position.

Both of these mean you will likely see less than battery voltage on FP and not have the proper current capacity for the pump.

When it is not starting, or not continuing to run, what effect do you see by using the COR by-pass jumper (connecting FP to B+ in the diagnostics connector)?
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Old 11-03-2018, 10:12 AM
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Originally Posted by Co_94_PU View Post
There are nearly 1.5 thousand pages in the service manual. You should not expect us to recall all of the specifications. Always try to include what the book says you should have for test results, at least provide a section and page number for the test you have undertaken.




So you have out of spec resistance between STA and E1. This means the COR won't be getting the current it needs/expects to close the contacts when the key is in the STArt position.

You have out of spec resistance between B+ and FC. This means the COR won't be getting the current it needs/expects to close the contacts when the VAFM switch is in the closed position.

Both of these mean you will likely see less than battery voltage on FP and not have the proper current capacity for the pump.

When it is not starting, or not continuing to run, what effect do you see by using the COR by-pass jumper (connecting FP to B+ in the diagnostics connector)?
Yes i am sorry. COR circuit opening relay. Might have been my auto correct. So are you saying being only 2 ohms off, that will deflect proper voltage?

Last edited by bensyota; 11-03-2018 at 10:14 AM.
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Old 11-03-2018, 10:17 AM
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Originally Posted by scope103 View Post
Optical Character Recognition? I'm going out on a limb here, and guessing you're working on the Circuit Opening Relay. Do you think that every person who might read your post has memorized the entire FSM, and knows what the "ohm test" is? Okay, I took the time to look up the manual on the COR http://web.archive.org/web/201003261...96circuito.pdf , and I don't see any test that involves an ohm reading. So I can't figure out what you are doing.


I assume "solenoid" refers to the starter solenoid, and you're unplugging it so you can hear the COR when you turn the key to STArt. If not, I don't know. From your description, it sounds like you have an intermittent problem, that may (but I'm thinking not) have something to do with heat-soak. My guess is a loose connection somewhere, possibly in the VAF-COR circuit.

To see if you're looking at the correct circuit, always carry your multimeter and a paper clip. If the truck dies, leave the key on and test for voltage on B+ to ground (diagnostic connector). If you have battery voltage (about 12.6v), use the paper clip to jumper B+ to FP. This bypasses the COR-VAF circuit and should force the fuel pump to run. If the truck starts, you've narrowed down the problem. If it still doesn't, it must be somewhere else.
I am sorry for not getting all the details. I am just getting anxious while writing these posts with info flowing through my head and hoping not to forget it!!

the one questionable test I have was checking for a click of the COR when opening flap in AFM with ignition in ON position. I did not hear it click. But like I said. I could immediately start it up and it would run just fine.

I duplicated the problem the other day by letting it idle for 15 min. Shutting it off. Coming back after 10 min it would start, chug and then die after giving it gas. I did jump the fp and b+ terminals in the diagnostics terminal and it started and ran fine. What does this tell me?

Last edited by bensyota; 11-03-2018 at 10:25 AM.
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Old 11-03-2018, 10:36 AM
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Originally Posted by bensyota View Post


I am sorry for not getting all the details. I am just getting anxious while writing these posts with info flowing through my head and hoping not to forget it!!

the one questionable test I have was checking for a click of the COR when opening flap in AFM with ignition in ON position. I did not hear it click. But like I said. I could immediately start it up and it would run just fine.

I duplicated the problem the other day by letting it idle for 15 min. Shutting it off. Coming back after 10 min it would start, chug and then die after giving it gas. I did jump the fp and b+ terminals in the diagnostics terminal and it started and ran fine. What does this tell me?
Until you consistently get this result "every time it dies I can jumper the diagnostics and it runs", it tells you nothing. Once you do have consistency, you know it's an issue somewhere in that circuit, it could be as simple as a loose or dirty connector in one of the plugs, it could be an abraded/broke wire, it could be the out of spec relay.
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Old 11-03-2018, 10:41 AM
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Interesting. The '93 manual I cited to (and my '94 manual at home) DON'T have the COR coil resistances. But Co_94_PU's does (what year?). All the more reason to be clear about what test you are running, and where you got it from. We all want to help.

If it starts, runs for a few seconds to cut-off, then by jumpering it works fine, that tells me you have a problem in the VAF-COR Circuit. The STArt signal from the ignition key is closing the COR through its coil, but FC switch in the VAF is not holding the COR closed once air flow starts. You have continuity through the second coil in the COR, so it's probably not burned out. You could have a sticky FC switch in the VAF, so it's not closing with air flow. Or (more likely), it's a bad connection somewhere in between.

I DON'T think your 136 ohm reading shows the COR is bad; your instrument may not even be that accurate, and the resistance you get can vary by two ohms depending on how hard you push on the leads. Heck, the leads on my good multimeter are 0.7 ohms themselves.

You could hook up your multimeter "permanently" to the FC connection at the COR. With key-on, you should get battery voltage (through the coil), that drops to (near) zero (ground) when the air flow closes the FC switch in the VAF. If you start the truck and it doesn't drop, then you're getting close. You still don't know if the problem is in the VAF or the wiring, but you could move the multimeter connection to the VAF and test again.

Last edited by scope103; 11-03-2018 at 10:42 AM.
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Old 11-03-2018, 10:52 AM
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I checked voltage on wiring going into COR when truck was running. I get 12+volts between fp-b+ and fc-b+. Which I think shows nothing really besides battery giving off voltage.
I thought I should get a voltage between fc and fp but their isnít any voltage. Should their be a voltage their? I donít see it as a test anywhere.
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Old 11-03-2018, 10:54 AM
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Originally Posted by scope103 View Post
Interesting. The '93 manual I cited to (and my '94 manual at home) DON'T have the COR coil resistances. But Co_94_PU's does (what year?). All the more reason to be clear about what test you are running, and where you got it from. We all want to help.

If it starts, runs for a few seconds to cut-off, then by jumpering it works fine, that tells me you have a problem in the VAF-COR Circuit. The STArt signal from the ignition key is closing the COR through its coil, but FC switch in the VAF is not holding the COR closed once air flow starts. You have continuity through the second coil in the COR, so it's probably not burned out. You could have a sticky FC switch in the VAF, so it's not closing with air flow. Or (more likely), it's a bad connection somewhere in between.

I DON'T think your 136 ohm reading shows the COR is bad; your instrument may not even be that accurate, and the resistance you get can vary by two ohms depending on how hard you push on the leads. Heck, the leads on my good multimeter are 0.7 ohms themselves.

You could hook up your multimeter "permanently" to the FC connection at the COR. With key-on, you should get battery voltage (through the coil), that drops to (near) zero (ground) when the air flow closes the FC switch in the VAF. If you start the truck and it doesn't drop, then you're getting close. You still don't know if the problem is in the VAF or the wiring, but you could move the multimeter connection to the VAF and test again.
do i test this with a probe on the fc wire going into relay and the other probe grounded?
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Old 11-03-2018, 11:51 AM
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Originally Posted by bensyota View Post
do i test this with a probe on the fc wire going into relay and the other probe grounded?
By definition, voltages are always between two points. By convention, when the other point is not mentioned explicitly, it's to ground. (This actually doesn't work with complex circuits, which can have multiple "grounds." But automotive is always a single ground, which is (most of) the metal of the vehicle.)

Originally Posted by bensyota View Post
... but their isn’t any voltage. ...
Get out of the habit of saying (anything like) that. 0.00 volts IS a voltage, so say it. This is even more true when measuring resistance. When someone says "I put my ohmmeter on the circuit, but I got nothing," we have no idea at all what he is talking about. Short? Open?

Originally Posted by bensyota View Post
I checked voltage on wiring going into COR when truck was running. I get 12+volts between fp-b+ and fc-b+. ...
Huh? That's 3 (4?) points. Voltage is between two points. If you measured between Fc and Fp, you should get 12v with the fuel pump running. Fc is a switch to ground, when the engine is running and the Fc switch is closed, that contact is at ground. Fp is direct to the fuel pump. When the COR is closed, it is connected to battery (~12v). Those two aren't on the same circuit, but there is a voltage between them.

If, instead, you measured between FP and B+, you should get 0v, as both of those are 12v to ground when running (so there is no voltage between them). Fc to B+ should give 12v, as Fc (when the switch is closed) is at ground.

Last edited by scope103; 11-03-2018 at 11:53 AM.
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Old 11-04-2018, 07:41 AM
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Originally Posted by scope103 View Post
Huh? That's 3 (4?) points. Voltage is between two points. If you measured between Fc and Fp, you should get 12v with the fuel pump running. Fc is a switch to ground, when the engine is running and the Fc switch is closed, that contact is at ground. Fp is direct to the fuel pump. When the COR is closed, it is connected to battery (~12v). Those two aren't on the same circuit, but there is a voltage between them.

If, instead, you measured between FP and B+, you should get 0v, as both of those are 12v to ground when running (so there is no voltage between them). Fc to B+ should give 12v, as Fc (when the switch is closed) is at ground.
all this checks out currently. I am currently letting it idle to try and duplicate the problem. I will check voltages again and then jump to the AFM and check resistances if it acts up. I see me having to act quick if it is a heat soak. It is cooler right now and shouldnít have to much time with the hood up to diagnosis it
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Old 11-04-2018, 01:16 PM
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Trying to figure out how to post pics from my phone
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Old 11-04-2018, 01:45 PM
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OKAY GUYS!!! This might show fault here! So with the truck cold, ign to ON and testing leads going into relay. Leads are reading 11vdc off of b+ to ground and 11vdc off of Fp to ground. With truck running itís reading 13vdc b+ To ground and 13vdc Fp to ground.

Now!!! I duplicated the issue. Started it while bogging and getting ready to die. The read was b+ 12vdc to ground and 12vdc Fc to ground!

The funny thing was that I pulled the COR off to test the resistances and they checked fine. Then I was going to go to the AFM and check resistance when running. But when I plugged the COR back in and started truck. You heard the contact close in the relay, the idle go to normal and the truck ran fine.

I am giving you guys these readings to please help me. Is this sign that the AFM Is closing the fuel switch but the contact is not closing in the relay? I checked the resistance on the AFM and they all read good. THA and E2 itís reading 1.35k ohms which is around 100 degrees Fahrenheit reading. The truck idled for a while and ran across town so im
guessing thatís normal. I held probes to contacts and ohms were slowly increasing so it seems okay

I am am going to try duplicating it again and see if I pull the relay and put back in, if it trips it again. Please help and thank you guys so much!!!!

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Old 11-04-2018, 03:32 PM
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What did the battery voltage read? At the posts, at the cable lugs, at the distribution block, at the efi main relay... Much lower than 11 and the ECU shuts off.
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Old 11-04-2018, 03:39 PM
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Originally Posted by Co_94_PU View Post
What did the battery voltage read? At the posts, at the cable lugs, at the distribution block, at the efi main relay... Much lower than 11 and the ECU shuts off.
you will have to explain this better to me Iím sorry. I am capable of doing all of it. But I have to understand what to do before I do it. Iím no expert but Iím willing to learn
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Old 11-04-2018, 05:41 PM
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Originally Posted by bensyota View Post

you will have to explain this better to me Iím sorry. I am capable of doing all of it. But I have to understand what to do before I do it. Iím no expert but Iím willing to learn
it is just a voltage test, looking for bad connections..

Keep the black probe on the negative battery post, touch the red probe to the other locations. They should all be very close to what you get with the res probe lead on the battery post.
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Old 11-04-2018, 09:18 PM
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Originally Posted by Co_94_PU View Post
it is just a voltage test, looking for bad connections..

Keep the black probe on the negative battery post, touch the red probe to the other locations. They should all be very close to what you get with the res probe lead on the battery post.
okay I got this and will test tomorow. But does the reading I got above not have a tell sign of anything? I mean when itís in problem mode Iím still reading 12vdc coming off Fc and not transferring to fuel pump?
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