Exhaust popping - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Rod_Lei · 01-31-2011, 04:07 PM

So I've got a C2500 350 with 298,000 miles on it. When I start it up in the morning, it runs great, but when it gets warm, the exhaust starts popping and I get a SES light with code 45 for rich exhaust. If I give it some gas for a few seconds the pops reduce a bit and the light disappears. The truck stops doing it when I drive it, but every once in a while I'll stop at a light or park the truck and I'll hear it popping. Has anyone had this problem?

ChevyTech · 01-31-2011, 05:15 PM

If it has a code 45, it is an OBD1 system, so it must be a TBI truck.

Anytime TBI runs to rich test the coolant sensor that the ECM monitors.

Specs are in this thread:
http://67-72chevytrucks.com/vboard/s...d.php?t=379142

Rod_Lei · 02-02-2011, 10:09 AM

Yeah I tested the CTS and it's working well. The idle works fine too. No high idle:/
Posted via Mobile Device

ChevLoRay · 02-02-2011, 12:49 PM

I read somewhere that a worn camshaft can cause a popping in the exhaust. 298K miles may be a good reason for a worn camshaft.

ChevyTech · 02-02-2011, 12:55 PM

The next thing I would test is the fuel pressure.

If the fuel return is blocked so the fuel cannot return to the tank the pressure will be higher then it should. This will cause it to go rich.

scotts62 · 02-02-2011, 02:12 PM

^^ i never thought of checking that or that it would make it run rich.. wow learn something every day

Mine pops like that too but if you just sit there and listen to it about every min or so it will just pop about 3x real fast like a dead hole then back to a good idle for a few more minutes.. i dunno lol

Ok i wont jack the thread so back to you

ChevLoRay · 02-02-2011, 02:15 PM

Before cleaning my MAF sensor, mine was doing something...not a miss, not a pop, but reminded me of a condensor going bad in an old school distributor. Oh, damp weather was more of an issue, too. Dry/low humidity? No problems.

Rod_Lei · 02-02-2011, 04:51 PM

Well it doesn't happen all the time. Just in the morning. The SES light comes on for a bit, if I drive it the light goes away and never comes back. I'm gonna change the Knock Sensor and the Manifold Absolute Pressure Sensor soon, maybe it will go away...

Rod_Lei · 02-08-2011, 11:04 AM

Does anyone think it could be the Diverter Valve? That's the only thing that I'm pretty sure is broken, but I'm not all too sure what he does...

ChevyTech · 02-08-2011, 03:24 PM

Yes a problem with the Diverter Valve can have a big affect on the oxygen sensor readings, and can cause popping in the exhaust.

Exhaust leaks:
Air getting in the exhaust system can affect the o2 reading. In open loop operation (cold) the ECM ignores the o2 sensor reading, but in closed loop (warm) the ECM uses the o2 reading to determine if the engine is running lean or rich. If the exhaust system leaks ahead of the o2 sensor, (or just behind it), the pulses in the exhaust will draw in air and cause the o2 sensor to get an incorrect reading. A vehicle with an A.I.R. will have the same problem if the air management valve allows air to be injected in the exhaust manifolds during closed loop operation.

The A.I.R. pump, pumps air into the exhaust manifolds, in OPEN loop operation, when the system is not using data from the O2 sensor to calibrate the amount of fuel to be injected.

In closed loop operation when the O2 sensor is being monitored air is diverted so no air is inject ahead of the O2 sensor.

You should make sure no air is getting injected to the Manifolds after the truck has warm enough to get to close loop operation. I would pinch and clamp the A.I.R hoses to the manifolds for testing.

The A I R management valves also stop the injection of air under some conditions to prevent explosions in the exhaust system.

Rod_Lei · 02-09-2011, 10:10 AM

Snap. Well maybe time for a new Diverter Valve? I'm thinking I can't remove it, it looks very involved in the engine management system:/ So what hoses do I plug? There is one going back around to the Manifold and one going to the Air Cleaner.

You guys are really great! Thanks for all your answers!!

ChevyTech · 02-09-2011, 10:24 AM

Quote:

So what hoses do I plug? There is one going back around to the Manifold and one going to the Air Cleaner.

Only the early TBI trucks had A I R (Air Injection Reaction), and it has been many years since I have seen one.

For testing the affect on the oxygen sensor:
You want to stop air from getting injected to the exhaust manifolds and many of the vehicles had rubber hose that looked like heater hoses between the AIR pump and the exhaust manifolds. I would pinch the AIR hoses to the exhaust manifolds off to test it.

For the popping you want to stop air injection downstream of the O2 sensor, which was often into the catalytic converter. I pinched off hoses for testing because it was quick.

If it has a separate belt for the A.I.R. pump you could remove the belt to test it.

Rod_Lei · 02-09-2011, 10:37 AM

Ok so do you think it would have an adverse effect if I pinched it off andkept it off?

I'm going to test it when the weather warms up.

ChevyTech · 02-09-2011, 10:53 AM

Only the early TBI trucks have the A.I.R. system so my guess is the trucks will run clean enough to meet pollution regulations without the pump.

I would not leave the pump on the truck with the hose pinched off. I would only do this to test it.

I have seen trucks with the system removed.

One advantage the A.I.R. system has is that the air pumped into the exhaust manifolds, in open loop, which burns the remaining fuel and helps warm up the oxygen sensor to get it into closed loop operation quicker.

Rod_Lei · 02-09-2011, 10:57 AM

I guess I can salvage it?

Rod_Lei · 02-13-2011, 09:01 PM

I think it's a one wire, not heated. But yeah I plugged up all the Diverter Valve hoses, much better!! Idles much lower and stronger, it's steady. But. It does kind of hesitate now. I mean it did before, but it ran so rich you couldn't tell. Now you can feel when you step on the gas it hesitates a bit. Could that be the timing advancing slowly?

ChevyTech · 02-14-2011, 11:42 AM

This is like playing 20 questions.

To give good guidance I need to know what you are working on.

So far I guess TBI because it has to be an OBD1 truck to have a code 45.

It must be a very early TBI truck to have A I R (Air Injection Reaction). 1988-1989?

The hesitation sounds like and EGR bog, or a low fuel pressure problem.

To discuss EGR I really need to know what you are working on because different gross vehicle weight trucks have different EGR systems. Let me know the transmission too.

You could try disconnecting and plugging the vacuum hose to the EGR valve and taking a test drive.

Rod_Lei · 02-14-2011, 03:51 PM

It is a 1988 2500 with the 5.7 350. I really don't know what transmission it has, I know it is auto with 4 gears. It does feel like EGR though, it has a new solenoid but I have to pull the valve and clean it. I have the hose from the throttle body to the solenoid plugged.

ChevyTech · 02-14-2011, 04:04 PM

Quote:

I have the hose from the throttle body to the solenoid plugged.

Did you just do this now for testing or was the vacuum hose disconnected & plugged when it was hesitating?

Rod_Lei · 02-14-2011, 04:23 PM

I plugged it when I removed the AIR hoses, it was plugged while I noticed the hesitation. I can still feel it.

ChevyTech · 02-14-2011, 06:41 PM

If it does not have the hesitation when it is cold before it gets to closed loop operation, then it could be the spark control retarding the timing because it has no EGR operation, and it is pinging when it gets in closed loop.

It would be a good idea to test the TPS.

Testing the fuel pressure would be a good idea but TBI trucks do not have a test port so it is more work, and takes more tools.

A worn distributor housing that lets the shaft wiggle sideways can cause problems on these trucks.

With all the popping, a bad cam lobe or two is a possibility.

When the head gasket fail between the center cylinders people have very different complaints, having trouble knowing just what is happening.

You may consider a compression test.

My first guess is that it has low fuel pressure.

Have you run it a bit and then checked for more trouble codes?

Rod_Lei · 02-15-2011, 08:55 AM

Hmmm yeah I've been driving it for a couple of days, no codes, not even the usual EGR failure code. I want to say it feels like a vacuum issue. I checked the distributor yesterday, no play in the shaft. I also took the TPS to Autozone, it is operating well. And the popping is now gone, so I hope it isn't an internal engine issue:P

Thanks a lot for your responses! Really it's guys like you all that make other peoples' lives easier.

ChevyTech · 02-15-2011, 12:03 PM

Thank you Rod Lei.

I think it is time to test the fuel pressure.

Rod_Lei · 02-15-2011, 12:11 PM

Ok. He's fixing to go to the shop sometime this month anyways, so I'll ask my friend to check the pressure and compression, I'm wondering if a headgasket is going, I've been adding water and can't find a leak...

Rod_Lei · 02-21-2011, 08:31 AM

Ok, checked the compression, all cylinders are doing good. The fuel pressure he said was right, put a new pump 3 years ago and a new filter last year. We worked on some vacuum hoses and now the truck no longer hesitates.

But now when you start the truck, the idle hunts, it can get pretty bad, but as soon as it warms up and goes into closed loop it runs perfectly, lot of power, quick response, and a rock solid idle.

Ha ha I'm beginning to wonder if my truck is just playing games with me...

01-31-2011, 04:07 PM	#1
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Exhaust popping So I've got a C2500 350 with 298,000 miles on it. When I start it up in the morning, it runs great, but when it gets warm, the exhaust starts popping and I get a SES light with code 45 for rich exhaust. If I give it some gas for a few seconds the pops reduce a bit and the light disappears. The truck stops doing it when I drive it, but every once in a while I'll stop at a light or park the truck and I'll hear it popping. Has anyone had this problem?

01-31-2011, 05:15 PM	#2
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Exhaust popping If it has a code 45, it is an OBD1 system, so it must be a TBI truck. Anytime TBI runs to rich test the coolant sensor that the ECM monitors. Specs are in this thread: http://67-72chevytrucks.com/vboard/s...d.php?t=379142 __________________ 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.

02-02-2011, 10:09 AM	#3
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Yeah I tested the CTS and it's working well. The idle works fine too. No high idle:/ Posted via Mobile Device

02-02-2011, 12:49 PM	#4
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Exhaust popping I read somewhere that a worn camshaft can cause a popping in the exhaust. 298K miles may be a good reason for a worn camshaft. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

02-02-2011, 12:55 PM	#5
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Exhaust popping The next thing I would test is the fuel pressure. If the fuel return is blocked so the fuel cannot return to the tank the pressure will be higher then it should. This will cause it to go rich. __________________ 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.

02-02-2011, 02:12 PM	#6
scotts62 One day... Join Date: Apr 2008 Location: Tuttle, Ok Posts: 9,243	Re: Exhaust popping ^^ i never thought of checking that or that it would make it run rich.. wow learn something every day Mine pops like that too but if you just sit there and listen to it about every min or so it will just pop about 3x real fast like a dead hole then back to a good idle for a few more minutes.. i dunno lol Ok i wont jack the thread so back to you __________________ Scott 93 crew cab build Project 62

02-02-2011, 02:15 PM	#7
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Exhaust popping Before cleaning my MAF sensor, mine was doing something...not a miss, not a pop, but reminded me of a condensor going bad in an old school distributor. Oh, damp weather was more of an issue, too. Dry/low humidity? No problems. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

02-02-2011, 04:51 PM	#8
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Well it doesn't happen all the time. Just in the morning. The SES light comes on for a bit, if I drive it the light goes away and never comes back. I'm gonna change the Knock Sensor and the Manifold Absolute Pressure Sensor soon, maybe it will go away...

02-08-2011, 11:04 AM	#9
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Does anyone think it could be the Diverter Valve? That's the only thing that I'm pretty sure is broken, but I'm not all too sure what he does...

02-08-2011, 03:24 PM	#10
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Exhaust popping Yes a problem with the Diverter Valve can have a big affect on the oxygen sensor readings, and can cause popping in the exhaust. Exhaust leaks: Air getting in the exhaust system can affect the o2 reading. In open loop operation (cold) the ECM ignores the o2 sensor reading, but in closed loop (warm) the ECM uses the o2 reading to determine if the engine is running lean or rich. If the exhaust system leaks ahead of the o2 sensor, (or just behind it), the pulses in the exhaust will draw in air and cause the o2 sensor to get an incorrect reading. A vehicle with an A.I.R. will have the same problem if the air management valve allows air to be injected in the exhaust manifolds during closed loop operation. The A.I.R. pump, pumps air into the exhaust manifolds, in OPEN loop operation, when the system is not using data from the O2 sensor to calibrate the amount of fuel to be injected. In closed loop operation when the O2 sensor is being monitored air is diverted so no air is inject ahead of the O2 sensor. You should make sure no air is getting injected to the Manifolds after the truck has warm enough to get to close loop operation. I would pinch and clamp the A.I.R hoses to the manifolds for testing. The A I R management valves also stop the injection of air under some conditions to prevent explosions in the exhaust system. __________________ 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.

02-09-2011, 10:10 AM	#11
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Snap. Well maybe time for a new Diverter Valve? I'm thinking I can't remove it, it looks very involved in the engine management system:/ So what hoses do I plug? There is one going back around to the Manifold and one going to the Air Cleaner. You guys are really great! Thanks for all your answers!!

02-09-2011, 10:37 AM	#13
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Ok so do you think it would have an adverse effect if I pinched it off andkept it off? I'm going to test it when the weather warms up.

02-09-2011, 10:53 AM	#14
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Exhaust popping Only the early TBI trucks have the A.I.R. system so my guess is the trucks will run clean enough to meet pollution regulations without the pump. I would not leave the pump on the truck with the hose pinched off. I would only do this to test it. I have seen trucks with the system removed. One advantage the A.I.R. system has is that the air pumped into the exhaust manifolds, in open loop, which burns the remaining fuel and helps warm up the oxygen sensor to get it into closed loop operation quicker. __________________ 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.

02-09-2011, 10:57 AM	#15
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping I guess I can salvage it?

02-13-2011, 09:01 PM	#16
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping I think it's a one wire, not heated. But yeah I plugged up all the Diverter Valve hoses, much better!! Idles much lower and stronger, it's steady. But. It does kind of hesitate now. I mean it did before, but it ran so rich you couldn't tell. Now you can feel when you step on the gas it hesitates a bit. Could that be the timing advancing slowly?



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02-14-2011, 11:42 AM	#17
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Exhaust popping This is like playing 20 questions. To give good guidance I need to know what you are working on. So far I guess TBI because it has to be an OBD1 truck to have a code 45. It must be a very early TBI truck to have A I R (Air Injection Reaction). 1988-1989? The hesitation sounds like and EGR bog, or a low fuel pressure problem. To discuss EGR I really need to know what you are working on because different gross vehicle weight trucks have different EGR systems. Let me know the transmission too. You could try disconnecting and plugging the vacuum hose to the EGR valve and taking a test drive. __________________ 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.

02-14-2011, 03:51 PM	#18
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping It is a 1988 2500 with the 5.7 350. I really don't know what transmission it has, I know it is auto with 4 gears. It does feel like EGR though, it has a new solenoid but I have to pull the valve and clean it. I have the hose from the throttle body to the solenoid plugged.

02-14-2011, 04:23 PM	#20
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping I plugged it when I removed the AIR hoses, it was plugged while I noticed the hesitation. I can still feel it.

02-14-2011, 06:41 PM	#21
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Exhaust popping If it does not have the hesitation when it is cold before it gets to closed loop operation, then it could be the spark control retarding the timing because it has no EGR operation, and it is pinging when it gets in closed loop. It would be a good idea to test the TPS. Testing the fuel pressure would be a good idea but TBI trucks do not have a test port so it is more work, and takes more tools. A worn distributor housing that lets the shaft wiggle sideways can cause problems on these trucks. With all the popping, a bad cam lobe or two is a possibility. When the head gasket fail between the center cylinders people have very different complaints, having trouble knowing just what is happening. You may consider a compression test. My first guess is that it has low fuel pressure. Have you run it a bit and then checked for more trouble codes? __________________ 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. Last edited by ChevyTech; 02-14-2011 at 11:14 PM. Reason: Spelling & add more

02-15-2011, 08:55 AM	#22
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Hmmm yeah I've been driving it for a couple of days, no codes, not even the usual EGR failure code. I want to say it feels like a vacuum issue. I checked the distributor yesterday, no play in the shaft. I also took the TPS to Autozone, it is operating well. And the popping is now gone, so I hope it isn't an internal engine issue:P Thanks a lot for your responses! Really it's guys like you all that make other peoples' lives easier.

02-15-2011, 12:03 PM	#23
ChevyTech Registered User Join Date: May 2004 Location: Minnesota Posts: 4,621	Re: Exhaust popping Thank you Rod Lei. I think it is time to test the fuel pressure. __________________ 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.

02-15-2011, 12:11 PM	#24
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Ok. He's fixing to go to the shop sometime this month anyways, so I'll ask my friend to check the pressure and compression, I'm wondering if a headgasket is going, I've been adding water and can't find a leak...

02-21-2011, 08:31 AM	#25
Rod_Lei Registered User Join Date: Jul 2010 Location: Waco, Texas Posts: 161	Re: Exhaust popping Ok, checked the compression, all cylinders are doing good. The fuel pressure he said was right, put a new pump 3 years ago and a new filter last year. We worked on some vacuum hoses and now the truck no longer hesitates. But now when you start the truck, the idle hunts, it can get pretty bad, but as soon as it warms up and goes into closed loop it runs perfectly, lot of power, quick response, and a rock solid idle. Ha ha I'm beginning to wonder if my truck is just playing games with me...

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