95 Tahoe Fuel pressure regulator question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dwntwn · 01-02-2013, 09:05 PM

Fixing this car for a friend, its a '95 TBI with 197,000 miles and she has been having intermittent stalling problems.

A local shop replaced her fuel pump, I checked the pressure, its almost 13 lbs, pinched the return line like ChevyTech outlined in the FAQ and the pressure surged, idle dropped substantially so I assumed it was the regulator spring.

Ordered a Borg Warner kit (P/N BWD 21732P $44.16) before I took the regulator apart, only to find the spring is intact.

The spring diaphragm doesn't have any holes, but is really thin and has some wrinkles. All the other gaskets in the throttle body are brittle, I am thinking I should go ahead and replace them anyway, but my question is, besides the spring, what else can go wrong with the regulator?

Is there anything besides the regulator that could cause the fuel pressure to spike when the return line is pinched off?

ChevyTech · 01-02-2013, 10:04 PM

The fuel pressure should spike when the fuel return line is pinched.

If the pressure is in the 11-13 PSI range with the engine running there is no need to restrict the fuel in the return line, to do any more testing.

If the fuel pressure is below specification, and restricting the return line raises the pressure, then the regulator spring could be broken.

If the pressure is around 9 PSI which is the bottom of the specification, you should test it at different engine speeds & loads. I have found if everything is in good condition the fuel pressure will not be at the bottom of the allowable range.

dwntwn · 01-02-2013, 10:31 PM

Thanks for the reply!

If the vehicle shows no trouble codes, but is having an intermittent stalling problem and the fuel pressure is in spec, can I assume the issue is caused by something else?

ChevyTech · 01-02-2013, 11:23 PM

You're welcome!

Does is stall only when the engine is warmed up?

Does it stall only at idle?

Have you had the distributor module tested?

dwntwn · 01-03-2013, 12:52 AM

It only stalls when warm, usually when coming to a stop or at idle. It will sometimes stumble at idle. (This is what she has told me...I drove the truck and it didn't stall for me)
I have not tested the distributor module but I can do that

ChevyTech · 01-03-2013, 11:38 AM

Heat could be causing the ignition module in the distributor to break down. Many stores like NAPA in my area will test the distributor module for free if you bring it in.

The test results from these stores are not always accurate, and some times the will say the module is good when it is not, but for a free test that may find the problem it is worth a try.

Make sure when you install or reinstall the distributor module that you use heat sink compound under it. The compound helps dissipate heat from the module. Without it, the module will fail.

Also check for a poor connection where the wires plug onto the distributor module.

Check for distributor wear:
http://67-72chevytrucks.com/vboard/s...9&postcount=48

The post above is from this thread on page two. This is a long thread with many of the TBI problems covered.
http://67-72chevytrucks.com/vboard/s...d.php?t=348308

dwntwn · 01-04-2013, 09:44 AM

Since I had taken the regulator off, I ordered a kit and cleaned and re-gasketed the throttle body before I put it back on... the throttle body was dirty and the gaskets were crusty. I also checked the TPS and IAC, (TPS was replaced in April) both checked out.
Then I pulled the distributor module and had it checked at ORielly's. It came up as being bad (I guess they test 16 things, it failed 6 of them) so I replaced that last night.
Waiting to drive it, I'll post how it goes. Thanks again for helping me figure this out, CT!

ChevyTech · 01-04-2013, 11:38 AM

You're welcome!

I will be watching for another reply to see if you say the problem is gone.

dwntwn · 01-07-2013, 01:01 AM

I had the battery disconnected and when I reconnected it, the alarm went off the other night. Unfortunately, it took me until today to get the details how to over-ride it.

I don't think it is related to the battery or alarm, but the truck will not start now.

I removed the #1 spark plug and cranked the motor, there is no spark. I even put the old distributor module on and tried that, no luck.

The only thing I did to the distributor was remove the cap, disconnect the plugs to the module and removed the rotor to inspect it. I put everything back together right and made sure everything was connected tight. It all seems ok

ChevyTech · 01-07-2013, 11:56 AM

The alarm could be preventing spark. Trace the wiring and look for relays.

Customers often would have us remove aftermarket alarms at the dealership once they had a problem with them.

Bad connections at the terminals of the distributor module are also common. A little bump of a wire can break the connection.

dwntwn · 01-07-2013, 01:22 PM

I'll check all the connections.

I did take a look under the dash and found this...does it look like the relay to you?

dwntwn · 01-07-2013, 03:25 PM

I'm not sure what did it, but I disconnected the battery and reset the alarm, then confirmed I had 12 volts at the coil, then reconnected everything with the new module and the truck starts and runs again. I think it was the plug that connects to the module that is under the cap that wasn't on tight. (the clip that holds it is gone)

ChevyTech · 01-07-2013, 05:10 PM

Quote:

I did take a look under the dash and found this...does it look like the relay to you?

That is not a relay, but it does look like the alarm box.

Quote:

I think it was the plug that connects to the module that is under the cap that wasn't on tight.

My guess is this was the problem.
Often the terminals no longer fit tight, and need to be tightened (bent) a little. It is a bigger problem with the connector terminals that plug on the outside connection of the distributor module.

dwntwn · 01-10-2013, 07:12 PM

Thanks again for all your help, CT!

ChevyTech · 01-10-2013, 09:42 PM

You're welcome!

A couple of days went by - no more questions, just a thank you - it must be fixed!

Excellent!

dwntwn · 01-17-2013, 08:24 AM

The truck runs a lot better, but the intermittent stalling has returned. It happens after the truck is warmed up with light throttle.
I was able to hold the throttle slightly open and noticed the EGR diaphragm was opening all the way (maybe 1000-1500 rpm) The EGR was checked it with a vacuum pump, seems seems ok.
Then I unplugged the EGR solenoid and the truck ran fine, thinking the solenoid wasn't doing its job. Plugged it back in and the EGR opened and the truck started to run lousy again. (Almost seems like its running on 4 cylinders—hard to describe)
So I replaced the $18 solenoid thinking it was bad, but it still hasn't solved the problem.
TBIs are still kind of new to me, but I'm guessing its the ECM that controls that solenoid, right? Is there anything else that could be causing the EGR to be at 100% with the throttle barely open?
Thanks again for you help, CT!

ChevyTech · 01-17-2013, 11:36 AM

You are making bad assumptions

Do not assume your truck has the same EGR without following the instrutions to see which EGR it has. Go read the WHOLE thread.

Quote:

On negative backpressure EGR systems the ECM powers the EGR solenoid when the engine might need EGR operation and it is the internal mechanism in the Negative backpressure EGR valve that modulates how much the EGR valve opens.

Here is a site with a good illustration of a negative backpressure EGR valve.
http://shbox.com/1/EGR_valve.jpg

The Negative backpressure EGR valve does the modulating and there is no great way to test it other then comparing the way it runs with a new EGR valve.

These TBI truck are very picky about the EGR valve operation.

I would suggest only using an OEM (Original equipment manufacturer) replacement EGR valve.

This quote is from post 58 on page 3 of the thread I posted a link to.
http://67-72chevytrucks.com/vboard/s...=348308&page=3

Quote:

Originally Posted by ChevyTech

The post above is from this thread on page two. This is a long thread with many of the TBI problems covered.
http://67-72chevytrucks.com/vboard/s...d.php?t=348308

This thread covers most of the common failures of the TBI trucks. Everything you have asked about is covered in the thread.

You can also use the search feature. I have discussed EGR operation many times.

dwntwn · 01-17-2013, 07:46 PM

Ok, I had no idea there were different styles of EGR. I don't have the truck here, but I know what to look for now
Thanks again for your help, CT!

dwntwn · 01-21-2013, 07:48 PM

I ordered a new Delco EGR, it will be here tomorrow, I'll post when I know if it fixed the problem

dwntwn · 01-23-2013, 04:53 PM

The EGR seems to have been the issue, the truck runs 100% better after having replaced it. Thanks again for your help, CT!

ChevyTech · 01-23-2013, 05:12 PM

You’re welcome, and thank you for letting us know what fixed it.

01-02-2013, 10:04 PM	#2
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: 95 Tahoe Fuel pressure regulator question The fuel pressure should spike when the fuel return line is pinched. If the pressure is in the 11-13 PSI range with the engine running there is no need to restrict the fuel in the return line, to do any more testing. If the fuel pressure is below specification, and restricting the return line raises the pressure, then the regulator spring could be broken. If the pressure is around 9 PSI which is the bottom of the specification, you should test it at different engine speeds & loads. I have found if everything is in good condition the fuel pressure will not be at the bottom of the allowable range. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

01-02-2013, 10:31 PM	#3
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question Thanks for the reply! If the vehicle shows no trouble codes, but is having an intermittent stalling problem and the fuel pressure is in spec, can I assume the issue is caused by something else? __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-02-2013, 11:23 PM	#4
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: 95 Tahoe Fuel pressure regulator question You're welcome! Does is stall only when the engine is warmed up? Does it stall only at idle? Have you had the distributor module tested? __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

01-03-2013, 12:52 AM	#5
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question It only stalls when warm, usually when coming to a stop or at idle. It will sometimes stumble at idle. (This is what she has told me...I drove the truck and it didn't stall for me) I have not tested the distributor module but I can do that __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-03-2013, 11:38 AM	#6
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: 95 Tahoe Fuel pressure regulator question Heat could be causing the ignition module in the distributor to break down. Many stores like NAPA in my area will test the distributor module for free if you bring it in. The test results from these stores are not always accurate, and some times the will say the module is good when it is not, but for a free test that may find the problem it is worth a try. Make sure when you install or reinstall the distributor module that you use heat sink compound under it. The compound helps dissipate heat from the module. Without it, the module will fail. Also check for a poor connection where the wires plug onto the distributor module. Check for distributor wear: http://67-72chevytrucks.com/vboard/s...9&postcount=48 The post above is from this thread on page two. This is a long thread with many of the TBI problems covered. http://67-72chevytrucks.com/vboard/s...d.php?t=348308 __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

01-02-2013, 09:05 PM	#1
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	95 Tahoe Fuel pressure regulator question Fixing this car for a friend, its a '95 TBI with 197,000 miles and she has been having intermittent stalling problems. A local shop replaced her fuel pump, I checked the pressure, its almost 13 lbs, pinched the return line like ChevyTech outlined in the FAQ and the pressure surged, idle dropped substantially so I assumed it was the regulator spring. Ordered a Borg Warner kit (P/N BWD 21732P $44.16) before I took the regulator apart, only to find the spring is intact. The spring diaphragm doesn't have any holes, but is really thin and has some wrinkles. All the other gaskets in the throttle body are brittle, I am thinking I should go ahead and replace them anyway, but my question is, besides the spring, what else can go wrong with the regulator? Is there anything besides the regulator that could cause the fuel pressure to spike when the return line is pinched off? __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-04-2013, 09:44 AM	#7
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question Since I had taken the regulator off, I ordered a kit and cleaned and re-gasketed the throttle body before I put it back on... the throttle body was dirty and the gaskets were crusty. I also checked the TPS and IAC, (TPS was replaced in April) both checked out. Then I pulled the distributor module and had it checked at ORielly's. It came up as being bad (I guess they test 16 things, it failed 6 of them) so I replaced that last night. Waiting to drive it, I'll post how it goes. Thanks again for helping me figure this out, CT! __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-04-2013, 11:38 AM	#8
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: 95 Tahoe Fuel pressure regulator question You're welcome! I will be watching for another reply to see if you say the problem is gone. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

01-07-2013, 01:01 AM	#9
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question I had the battery disconnected and when I reconnected it, the alarm went off the other night. Unfortunately, it took me until today to get the details how to over-ride it. I don't think it is related to the battery or alarm, but the truck will not start now. I removed the #1 spark plug and cranked the motor, there is no spark. I even put the old distributor module on and tried that, no luck. The only thing I did to the distributor was remove the cap, disconnect the plugs to the module and removed the rotor to inspect it. I put everything back together right and made sure everything was connected tight. It all seems ok __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-07-2013, 11:56 AM	#10
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: 95 Tahoe Fuel pressure regulator question The alarm could be preventing spark. Trace the wiring and look for relays. Customers often would have us remove aftermarket alarms at the dealership once they had a problem with them. Bad connections at the terminals of the distributor module are also common. A little bump of a wire can break the connection. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

01-07-2013, 01:22 PM	#11
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question I'll check all the connections. I did take a look under the dash and found this...does it look like the relay to you? Attached Images __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-07-2013, 03:25 PM	#12
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question I'm not sure what did it, but I disconnected the battery and reset the alarm, then confirmed I had 12 volts at the coil, then reconnected everything with the new module and the truck starts and runs again. I think it was the plug that connects to the module that is under the cap that wasn't on tight. (the clip that holds it is gone) __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-10-2013, 07:12 PM	#14
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question Thanks again for all your help, CT! __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-10-2013, 09:42 PM	#15
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: 95 Tahoe Fuel pressure regulator question You're welcome! A couple of days went by - no more questions, just a thank you - it must be fixed! Excellent! __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

01-17-2013, 08:24 AM	#16
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question The truck runs a lot better, but the intermittent stalling has returned. It happens after the truck is warmed up with light throttle. I was able to hold the throttle slightly open and noticed the EGR diaphragm was opening all the way (maybe 1000-1500 rpm) The EGR was checked it with a vacuum pump, seems seems ok. Then I unplugged the EGR solenoid and the truck ran fine, thinking the solenoid wasn't doing its job. Plugged it back in and the EGR opened and the truck started to run lousy again. (Almost seems like its running on 4 cylinders—hard to describe) So I replaced the $18 solenoid thinking it was bad, but it still hasn't solved the problem. TBIs are still kind of new to me, but I'm guessing its the ECM that controls that solenoid, right? Is there anything else that could be causing the EGR to be at 100% with the throttle barely open? Thanks again for you help, CT! __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG



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01-17-2013, 07:46 PM	#18
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question Ok, I had no idea there were different styles of EGR. I don't have the truck here, but I know what to look for now Thanks again for your help, CT! __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-21-2013, 07:48 PM	#19
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question I ordered a new Delco EGR, it will be here tomorrow, I'll post when I know if it fixed the problem __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-23-2013, 04:53 PM	#20
dwntwn Registered User Join Date: Oct 2012 Location: Tucson, AZ Posts: 101	Re: 95 Tahoe Fuel pressure regulator question The EGR seems to have been the issue, the truck runs 100% better after having replaced it. Thanks again for your help, CT! __________________ _____________________________________________ 1966 c10, short fleet, 402ci 700r4 1988 r20 Suburban 454ci tbi, th400 (12v Cummins soon) 1980 shovelhead, hardtail, open primary 1998 FXDWG

01-23-2013, 05:12 PM	#21
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: 95 Tahoe Fuel pressure regulator question You’re welcome, and thank you for letting us know what fixed it. __________________ For those of you that are wondering why you are not getting replies to your thread: Did you give the model, year, engine, fuel system type, and transmission information? If it is modified from what came stock from the factory, let us know that too.

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