Engine surging

dbanks12 · 06-29-2009, 09:41 AM

Hi I have a 94 GMC Silverado with a 5.7 Litre in it. I was driving it last week and when I went up a hill I lost power. I pulled over and it was surging even at idle, my dreaded check engine light was on. I have a code reader and when I got it home found a 44 o2 sensor. I have since replaced the sensor and changed a fuel filter for good measure. Started it up and it ran at idle but when I put it in gear it dies and is surging again. I took my air cleaner and clearance ring off the throttle body and both injectors are spraying evenly even when it dies out. Now the o2 sensor code is back, I checked it over and it only has one o2 sensor in it. Any help would be appreciated

**octaneman** · 06-29-2009, 10:25 AM

Hi dbanks12

After you replaced the O2 sensor did you erase the codes ? When replacing a sensor it is always a good idea to erase the codes. To do this, disconnect the battery for 5 min. The problem with that sometimes is that the settings for transmission ( cars equiped with transmission ECM) also get lost causing drivability issues. To correct it, the car has to be driven for several kilometers in order to re-set the ECM.

dbanks12 · 06-30-2009, 10:04 AM

I did disconnect the battery after and cleared the code, not other codes present. My Chilton's book isn't much help on this problem, no trouble shooting chart. When I start it up it goes on high idle like it should and unless I step on the gas it just dies out and putting it in gear makes it die as well. I did check out the map sensor and I have the required voltage both with the key on and running so that doesn't seem to be the issue. When I unplug the vacuum hose from the map sensor it runs great but eventually dies when in gear. I'm stumped on this one completely. Wish I could switch it over to a carburetor...

**octaneman** · 06-30-2009, 11:05 AM

Check for vacuum leaks from the intake manifold and surrounding hoses including the brake booster, also be sure that the EGR valve is working properly and it isn't stuck open. If the car is equipped with a vacuum reservoir make sure that it isn't cracked or broken including the air filter housing and the intake pipe. Check the mass air flow sensor with DVOM using the frequency scale, the mass airflow sometimes does not set any codes but it's a major culprit that causes major problems such as rough idle, stalling, stumble, and other symptoms. A quick check to see if the mass air flow is working is by starting the engine and using a screwdriver tap on it and watch the engine's reaction. If its bad you will notice a change in engine behavior instantly.

post back your findings.

dbanks12 · 07-01-2009, 02:06 PM

Checked for vacuum leaks, everything good. Also took out the EGR valve and it is moving good, cleaned it just for good measure. There is a module between the lower throttle body vacuum and the EGR that I took out and cleaned as well, that's okay. The TBI throttle body's don't have a mass air flow sensor they have a air idle control module that screws into the throttle body just behind the throttle position sensor and sometimes get plugged or stuck. I took that out sprayed carb cleaner into the hole and it's clear as well as the sensor holding it vertical like the book says.

I checked voltage on the throttle position sensor and it's within range. I also checked for ohms on the idle air control module, the book asks for 2 measurements at the different posts and says they should be infinite, however I have a digital meter and one side was -10.5 and the other side was-105. Not to sure what they mean by infinite?

Still if I unplug the vacuum hose to the map sensor idle comes up to normal and it runs great until I put it in gear.I thought it may be a fuel pump because I ran it low and kicked the tank once to get it going but fuel is okay and pump is running. The vacuum hoses are in good shape, I didn't try taking the hose off of the brake booster but someone replaced all the hoses under the hood, like new.Any other thoughts?

**octaneman** · 07-01-2009, 03:53 PM

On the ohm meter when the readings are specified as infinity its as if the meter doesn't see anything, it should not read for example:0.00 It should have something to indicate infinity (check your manual for scale readings). 0 readings mean just that ..zero. but it is NOT infinity. The readings you posted leads me to believe that the positive and negative leads were reversed giving a negative reading. Please re-check :) There is also another test to do on the idle solenoid by using a 9v battery. Connect the battery to the soleniod and see if the solenoid motor works, if it works properly the plunger should extend outwards, then you reverse polarity and see if the plunger retracts. This will indicate if there any dead spots on the IAC motor. Here's a great link to show you how to test your sensors.

YouTube - Auto Repair: Idle Speed Control - Testing and Replacing

YouTube - Auto Repair: M.A.P./Vacuum Sensors - Testing and Replacing (1 of 2)

YouTube - Auto Repair: Oxygen Sensors - Testing and Replacing (1 of 2)

Please post your readings of the MAP sensor ,IAC , Oxygen sensor.

please post back your readings.

dbanks12 · 07-02-2009, 11:25 AM

O2 sensor is new and the map sensor is as well, had a spare one. I tried the tests for the IAC and the tip is working. The gear is not moving at all, just feel a small tic but no movement, not going in or out. Guess that sums it up, wish they would put that simple test in a book. I will buy a new one today and install, will let you know the results.

dbanks12 · 07-04-2009, 04:44 PM

Bought a new IAC sensor and it runs and idles, took it for a drive at 40 k and the sensors reset just like the book said they would. It still wants to stall when I put it under load, in gear or accelerating but other than that runs good so I guess the fuel pump is on it's way out.

I looked at the diagram and there's only one wire to the tank so putting a pump on the rail is out of the question as it operates the sending unit as well. So it's off to the shop I can pick up a pump for $93.00 and they can install for $200.00. At least I know the O2 sensor is fixed and the IAC is as well. Can't think of anything else it could be and the fact that I kicked the tank once when draining it to low sure sounds like my last piece of the puzzle.

**octaneman** · 07-04-2009, 07:10 PM

Good job dbanks12

But before you decide to scrap the pump, hook up a fuel pressure gage and take the pressure readings in park and then again in drive while you hold down the brake pedal. Note the difference, then repeat the test by disconnecting the fuel pressure regulator and see if it wants to stall out under load, if the pressure goes up the engine should smooth out and the regulator works, if pressure remains the same or drops then the regulator is not functioning. If the regulator does pass the test and the pressure gage moves erratic or is not stable then the pump is on its last legs.

dbanks12 · 07-05-2009, 11:11 AM

I have a TBI throttle body on this truck and looking through the book I don't see any fuel regulator, If it was a CFSI it would be right behind the throttle body but all I have is a fuel line. Could it be anywhere else?

**octaneman** · 07-06-2009, 03:19 AM

The fuel regulator on the TBI is right on top of the TBI between the injector. It has a goldish color shaped like a cup. The regulator is adjustable and some mechanics are brave enough to mess with it, but I don't recommend it because it is set from factory. To check the fuel pump pressure, by putting the gage on a T fitting on the inlet side of the TBI and turning the key on. Now, the regulator should have 9-13 psi going into the injectors.

dbanks12 · 07-06-2009, 08:28 AM

I looked in my Chilton,s book and of course it only shows removal of injectors. I think your talking about the piece just under them. I don't have a fuel gauge but can pick one up and the T, I know I have two metal lines behind the throttle body, a small one and a big one. Which one do I put the T on.

I will buy the gauge and do the test, will send you the results. If it is low can I replace the regulator?

**octaneman** · 07-06-2009, 11:04 AM

The fuel inlet is the big one and the small one is the return, both inlet and outlet are on the same side facing the regulator. The outlet should be at an angle the inlet is straight in. Place the T on the inlet side. If the fuel pump pressure at the regulator fails the test, yes you can replace it, as long as fuel pressure is constant at the pump. Make sure you get the gasket kit for the TBI if you replace it.

dbanks12 · 07-06-2009, 08:00 PM

I'm going to pick up the tester tomorrow and I see the inlet no problem. According to Gm if I have 12 - 15 psi on the inlet with key on which is a little different than the 9 - 13 not sure which measurement to use. But if I take off return and block and pressure goes up it's the regulator if it doesn't it's the fuel pump, does that sound right or am I a little ahead of myself. Well if I didn't know TBI'S I sure do now and everything connected to it.

**octaneman** · 07-06-2009, 10:18 PM

Use Gm's specification from 12 - 15 psi, as for the procedure to set up your tester to check the pressure you got it dead on. Keep in mind that once you block the return, the pressure is EXPECTED to go up because the return is blocked and the excess fuel has nowhere to go. The regulator is bad if the pressure FLUCTUATES or if it remains BELOW regulator specs pressure. For example: Fuel pump specs say 30 psi at the line. With return blocked, spec sheet says 12 -15 at the regulator. Your reading shows 9, then the diagnosis is that the regulator is history. If the pressure goes exactly to specs 12 - 15 or slightly above, then the regulator is OK.

For the fuel pump to be bad, you reconnect the return line to the TBI body. Connect the gas line inlet pipe DIRECTLY TO THE GAGE, turn the key on and the line will pressurize, and the gage will read the pump's maximum pressure output. Should the pressure be BELOW your spec sheet then you can say bye-bye to the pump.

dbanks12 · 07-15-2009, 07:34 PM

Tested the pump pressure by taking the line off and hooking the gauge directly to the line. The gauge was only registering about 3 psi, turned it off bled the line and tried it again 9 psi. but after I opened the bleed valve and closed it on the gauge it dropped back down to 2 psi and didn't climb back up. I opened up the end of the hose and put it in a bucket and had gas flowing slowly, very slowly didn't seem anything close to 12 - 15 psi like the book says so I guess it's the pump, I can hear the pump making noise and the hum seems louder than it use to.

**octaneman** · 07-15-2009, 08:29 PM

Congrats ! dbanks12

You nailed it ! Once your pump is replaced the truck should be purring like a kitten.

dbanks12 · 07-16-2009, 07:54 AM

Octaneman, I would just like to say thanks for all your help. Although I have rebuilt more than my share of motors & cars in my time this is the first TBI equipped vehicle I have ever dealt with. Thanks to people like you and a good repair book even an old timer like me can figure things out so way to go yourself. Will advise next Wednesday when it's in, can't wait to hit the highway again.

dbanks12 · 07-22-2009, 08:06 AM

Octaneman, took off the box cleaned the top of the tank off and replaced the pump and screen. It runs perfect. I opened up the old pump just to take a look the brushes were worn right out and amazingly the impeller was still okay. Thanks again for all your help, the book was good to have but having someone guiding you was priceless.

**octaneman** · 07-23-2009, 01:23 AM

Your welcome anytime dbanks12, glad I can help you out.

06-29-2009, 09:41 AM	#1 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Engine surging Hi I have a 94 GMC Silverado with a 5.7 Litre in it. I was driving it last week and when I went up a hill I lost power. I pulled over and it was surging even at idle, my dreaded check engine light was on. I have a code reader and when I got it home found a 44 o2 sensor. I have since replaced the sensor and changed a fuel filter for good measure. Started it up and it ran at idle but when I put it in gear it dies and is surging again. I took my air cleaner and clearance ring off the throttle body and both injectors are spraying evenly even when it dies out. Now the o2 sensor code is back, I checked it over and it only has one o2 sensor in it. Any help would be appreciated

06-29-2009, 10:25 AM	#2 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging Hi dbanks12 After you replaced the O2 sensor did you erase the codes ? When replacing a sensor it is always a good idea to erase the codes. To do this, disconnect the battery for 5 min. The problem with that sometimes is that the settings for transmission ( cars equiped with transmission ECM) also get lost causing drivability issues. To correct it, the car has to be driven for several kilometers in order to re-set the ECM.

06-30-2009, 10:04 AM	#3 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging I did disconnect the battery after and cleared the code, not other codes present. My Chilton's book isn't much help on this problem, no trouble shooting chart. When I start it up it goes on high idle like it should and unless I step on the gas it just dies out and putting it in gear makes it die as well. I did check out the map sensor and I have the required voltage both with the key on and running so that doesn't seem to be the issue. When I unplug the vacuum hose from the map sensor it runs great but eventually dies when in gear. I'm stumped on this one completely. Wish I could switch it over to a carburetor...

06-30-2009, 11:05 AM	#4 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging Check for vacuum leaks from the intake manifold and surrounding hoses including the brake booster, also be sure that the EGR valve is working properly and it isn't stuck open. If the car is equipped with a vacuum reservoir make sure that it isn't cracked or broken including the air filter housing and the intake pipe. Check the mass air flow sensor with DVOM using the frequency scale, the mass airflow sometimes does not set any codes but it's a major culprit that causes major problems such as rough idle, stalling, stumble, and other symptoms. A quick check to see if the mass air flow is working is by starting the engine and using a screwdriver tap on it and watch the engine's reaction. If its bad you will notice a change in engine behavior instantly. post back your findings.

07-01-2009, 02:06 PM	#5 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging Checked for vacuum leaks, everything good. Also took out the EGR valve and it is moving good, cleaned it just for good measure. There is a module between the lower throttle body vacuum and the EGR that I took out and cleaned as well, that's okay. The TBI throttle body's don't have a mass air flow sensor they have a air idle control module that screws into the throttle body just behind the throttle position sensor and sometimes get plugged or stuck. I took that out sprayed carb cleaner into the hole and it's clear as well as the sensor holding it vertical like the book says. I checked voltage on the throttle position sensor and it's within range. I also checked for ohms on the idle air control module, the book asks for 2 measurements at the different posts and says they should be infinite, however I have a digital meter and one side was -10.5 and the other side was-105. Not to sure what they mean by infinite? Still if I unplug the vacuum hose to the map sensor idle comes up to normal and it runs great until I put it in gear.I thought it may be a fuel pump because I ran it low and kicked the tank once to get it going but fuel is okay and pump is running. The vacuum hoses are in good shape, I didn't try taking the hose off of the brake booster but someone replaced all the hoses under the hood, like new.Any other thoughts?

07-01-2009, 03:53 PM	#6 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging On the ohm meter when the readings are specified as infinity its as if the meter doesn't see anything, it should not read for example:0.00 It should have something to indicate infinity (check your manual for scale readings). 0 readings mean just that ..zero. but it is NOT infinity. The readings you posted leads me to believe that the positive and negative leads were reversed giving a negative reading. Please re-check :) There is also another test to do on the idle solenoid by using a 9v battery. Connect the battery to the soleniod and see if the solenoid motor works, if it works properly the plunger should extend outwards, then you reverse polarity and see if the plunger retracts. This will indicate if there any dead spots on the IAC motor. Here's a great link to show you how to test your sensors. YouTube - Auto Repair: Idle Speed Control - Testing and Replacing YouTube - Auto Repair: M.A.P./Vacuum Sensors - Testing and Replacing (1 of 2) YouTube - Auto Repair: Oxygen Sensors - Testing and Replacing (1 of 2) Please post your readings of the MAP sensor ,IAC , Oxygen sensor. please post back your readings. Last edited by octaneman; 07-01-2009 at 04:03 PM.

07-02-2009, 11:25 AM	#7 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging O2 sensor is new and the map sensor is as well, had a spare one. I tried the tests for the IAC and the tip is working. The gear is not moving at all, just feel a small tic but no movement, not going in or out. Guess that sums it up, wish they would put that simple test in a book. I will buy a new one today and install, will let you know the results.

07-04-2009, 04:44 PM	#8 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging Bought a new IAC sensor and it runs and idles, took it for a drive at 40 k and the sensors reset just like the book said they would. It still wants to stall when I put it under load, in gear or accelerating but other than that runs good so I guess the fuel pump is on it's way out. I looked at the diagram and there's only one wire to the tank so putting a pump on the rail is out of the question as it operates the sending unit as well. So it's off to the shop I can pick up a pump for $93.00 and they can install for $200.00. At least I know the O2 sensor is fixed and the IAC is as well. Can't think of anything else it could be and the fact that I kicked the tank once when draining it to low sure sounds like my last piece of the puzzle.

07-04-2009, 07:10 PM	#9 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging Good job dbanks12 But before you decide to scrap the pump, hook up a fuel pressure gage and take the pressure readings in park and then again in drive while you hold down the brake pedal. Note the difference, then repeat the test by disconnecting the fuel pressure regulator and see if it wants to stall out under load, if the pressure goes up the engine should smooth out and the regulator works, if pressure remains the same or drops then the regulator is not functioning. If the regulator does pass the test and the pressure gage moves erratic or is not stable then the pump is on its last legs.

07-05-2009, 11:11 AM	#10 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging I have a TBI throttle body on this truck and looking through the book I don't see any fuel regulator, If it was a CFSI it would be right behind the throttle body but all I have is a fuel line. Could it be anywhere else?

07-06-2009, 03:19 AM	#11 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging The fuel regulator on the TBI is right on top of the TBI between the injector. It has a goldish color shaped like a cup. The regulator is adjustable and some mechanics are brave enough to mess with it, but I don't recommend it because it is set from factory. To check the fuel pump pressure, by putting the gage on a T fitting on the inlet side of the TBI and turning the key on. Now, the regulator should have 9-13 psi going into the injectors.

07-06-2009, 08:28 AM	#12 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging I looked in my Chilton,s book and of course it only shows removal of injectors. I think your talking about the piece just under them. I don't have a fuel gauge but can pick one up and the T, I know I have two metal lines behind the throttle body, a small one and a big one. Which one do I put the T on. I will buy the gauge and do the test, will send you the results. If it is low can I replace the regulator?

07-06-2009, 11:04 AM	#13 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging The fuel inlet is the big one and the small one is the return, both inlet and outlet are on the same side facing the regulator. The outlet should be at an angle the inlet is straight in. Place the T on the inlet side. If the fuel pump pressure at the regulator fails the test, yes you can replace it, as long as fuel pressure is constant at the pump. Make sure you get the gasket kit for the TBI if you replace it. Last edited by octaneman; 07-06-2009 at 11:13 AM.

07-06-2009, 08:00 PM	#14 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging I'm going to pick up the tester tomorrow and I see the inlet no problem. According to Gm if I have 12 - 15 psi on the inlet with key on which is a little different than the 9 - 13 not sure which measurement to use. But if I take off return and block and pressure goes up it's the regulator if it doesn't it's the fuel pump, does that sound right or am I a little ahead of myself. Well if I didn't know TBI'S I sure do now and everything connected to it. Last edited by dbanks12; 07-06-2009 at 08:02 PM.

07-06-2009, 10:18 PM	#15 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging Use Gm's specification from 12 - 15 psi, as for the procedure to set up your tester to check the pressure you got it dead on. Keep in mind that once you block the return, the pressure is EXPECTED to go up because the return is blocked and the excess fuel has nowhere to go. The regulator is bad if the pressure FLUCTUATES or if it remains BELOW regulator specs pressure. For example: Fuel pump specs say 30 psi at the line. With return blocked, spec sheet says 12 -15 at the regulator. Your reading shows 9, then the diagnosis is that the regulator is history. If the pressure goes exactly to specs 12 - 15 or slightly above, then the regulator is OK. For the fuel pump to be bad, you reconnect the return line to the TBI body. Connect the gas line inlet pipe DIRECTLY TO THE GAGE, turn the key on and the line will pressurize, and the gage will read the pump's maximum pressure output. Should the pressure be BELOW your spec sheet then you can say bye-bye to the pump. Last edited by octaneman; 07-06-2009 at 10:29 PM.

07-15-2009, 07:34 PM	#16 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging Tested the pump pressure by taking the line off and hooking the gauge directly to the line. The gauge was only registering about 3 psi, turned it off bled the line and tried it again 9 psi. but after I opened the bleed valve and closed it on the gauge it dropped back down to 2 psi and didn't climb back up. I opened up the end of the hose and put it in a bucket and had gas flowing slowly, very slowly didn't seem anything close to 12 - 15 psi like the book says so I guess it's the pump, I can hear the pump making noise and the hum seems louder than it use to.

07-15-2009, 08:29 PM	#17 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging Congrats ! dbanks12 You nailed it ! Once your pump is replaced the truck should be purring like a kitten.

07-16-2009, 07:54 AM	#18 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging Octaneman, I would just like to say thanks for all your help. Although I have rebuilt more than my share of motors & cars in my time this is the first TBI equipped vehicle I have ever dealt with. Thanks to people like you and a good repair book even an old timer like me can figure things out so way to go yourself. Will advise next Wednesday when it's in, can't wait to hit the highway again.

07-22-2009, 08:06 AM	#19 (permalink)
dbanks12 Registered User Join Date: Jun 2009 Posts: 11 OS: xp professional sp3	Re: Engine surging Octaneman, took off the box cleaned the top of the tank off and replaced the pump and screen. It runs perfect. I opened up the old pump just to take a look the brushes were worn right out and amazingly the impeller was still okay. Thanks again for all your help, the book was good to have but having someone guiding you was priceless.

07-23-2009, 01:23 AM	#20 (permalink)
octaneman Mentor Home Support, Gearhead Automotive Center Join Date: May 2009 Posts: 543 OS: WINXP	Re: Engine surging Your welcome anytime dbanks12, glad I can help you out. Last edited by octaneman; 07-23-2009 at 01:47 AM.