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 Post subject: Quote of the day: "Why are the headers glowing?"
PostPosted: Tue Jun 16, 2009 5:47 am 
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Location: Orange County, CA
That was what my wife asked me while we were driving the Astro tonight. Let me fill you in...

I have been trying to diagnose an off idle hesitation and general lack of power with my van for quite a long time. Tonight I connected a vacuum gauge to a manifold vacuum source and went for a drive. My wife had some errands to run so she hopped in the van and off we went. It's dark outside and we were driving with the doghouse removed (Isn't she great!) and after we had been on the freeway a while I notice she is staring at the floor. I asked what she was looking at and she says "Why are the headers glowing?". I looked over at the passenger side of the motor and sure enough the right exhaust manifold is glowing like an electric toaster!

Now here are my questions:
1) Why is the left manifold iron while the right side is steel?
2) Why is the steel manifold getting hot enough to glow?
3) Should I be very worried about this?

Here are answers to questions you all may have:
- We are dealing with the 4.3 V6.
- The engine does not overheat.
- It does not have headers, 100% stock exhaust.
- Catalytic converter is 1 year old.
- The engine is stock with the exception of an injector pod spacer and adjustable fuel pressure regulator.
- The fuel pressure is set at 14 psi.
- Spark timing is set to spec at 0 degrees with the timing connector disconnected.
- Spark plugs are the correct AC Delco application for this vehicle.
- Manifold vacuum is 19in at idle and less than 5in at 65mph in overdrive. (Good?)
- The needle on the vacuum gauge is steady at all times.
- The glow starts really anytime the engine is under load, and gets brighter as the load increases.
- I have no idea how long this has been going on.

I imagine that the exhaust temperature is the same on both sides of the motor, but it's probably just not hot enough for the iron manifold to glow. Do you agree?

Glowing exhaust is generally an indication of a lean fuel mix, right?

Has anyone else witnessed this with their vans? Or, would anyone else want to go for a drive at night with the cover off and see if their van does it? It keeps you nice and warm!!

Thanks in advance!

Edit: This might be more appropriate in the Exhaust forum. Rob, please feel free to move it if you see fit.

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Tue Jun 16, 2009 8:54 am 
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Why would one side have a cast iron manifold while the other is steel? I have iron on both sides of my 92.

As for the idle, do you have TBI or straight carb? If it is TBI, when was the last time the Idle Air Control was cleaned?

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Tue Jun 16, 2009 12:01 pm 
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One side iron,one side steel ......somethings not right!
Anyways(steel) headers are going to glow.Thinner material and prone to heat quicker than cast. End of story. Daylight you wouldn't see it, is all.
As for your idle ...?

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Tue Jun 16, 2009 2:28 pm 
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Location: British Columbia
For reasons unknown to me, that is the way they made some of the earlier vans - 1 cast iron manifold & 1 (poor quaility) stainless steel header. So don't worry about that ... normal, but curiosity is good.

The most obvious answer is the correct answer. Thinner material heats up faster. In addition, you would probably not notice the glow if you were driving during the day but at night, in the dark, it is a whole different game.

Jumping to your last question, there is different degrees of glowing so how bright is normal. Temperature. Compare left & right temperatures of the exhaust 'Y' pipe after driving, not the manifold.

As to your hesitation & general lack of power, have your disconnected your EGR valve?

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Wed Jun 17, 2009 3:47 am 
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Location: Orange County, CA
Quote:
As for the idle, do you have TBI or straight carb? If it is TBI, when was the last time the Idle Air Control was cleaned?

It is TBI. The throttle body was removed and cleaned and had new throttle shaft bushings installed within the last year. At that time the IAC passage in the TBI and the IAC itself were both cleaned.

Quote:
As to your hesitation & general lack of power, have your disconnected your EGR valve?

The EGR valve has been replaced with a new GM part, within the last two years. I have also driven with the EGR vacuum disconnected and plugged, it did not change the symptoms.

I am going to try and get a picture of the glow tonight, tomorrow I will remember to bring my IR temp gun home and check the temperatures of the Y pipe.

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Wed Jun 17, 2009 10:48 am 
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14psi is too high for TBI motors if it is all stock. 9-13psi max according to GM. Have you tried backing it down to say 11-12psi to see what happens?

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Sun Jun 21, 2009 4:19 am 
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Before I installed the adjustable regulator the fuel pressure was at 12psi. Unfortunately the van ran the same then as it does now.

I took some pictures but they did not come out well at all. Where I see a bright orange glow the camera sees a pale purple, or sometimes blue.

I brought my IR temp gun home but I forgot to use it. ](*,)
I'll go for a drive tomorrow and get some temperature readings.

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Wed Jun 24, 2009 5:41 am 
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I checked the temperatures tonight as v8famvan described. Both sides of the Y pipe are in the mid 500F range.
Does that sound right?

Also, regarding the driveability symptoms, another person has suggested that the distributor could be the cause because it may have become "magnetized".
He described how to check it:
With the timing connector disconnected, note the base timing setting with a timing light. At 2000 rpm the timing should advance 6-10 degrees, he says. If it retards, or does not advance at all the distributor is bad.

What do you guys think of this? Does it sound plausible? I plan to check it out anyway, just to see what it does. But, if it fails this test I would really like your opinions before I buy a distributor. I bet they're expensive!

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Thu Jun 25, 2009 3:55 am 
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Well, I did the distributor test and the timing advanced just as he said it should. However, because the problem is intermittent it may not have been acting up while I was testing it.
Any thoughts?

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Thu Jun 25, 2009 10:40 am 
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I just read your first post, again. It may be normal. I'm not sure what normal exhaust temps are but they could very well be that high. If I remember right combustion temps are around 1800. If everything else is OK then I wouldn't be too concerned. \:D/

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Fri Jun 26, 2009 3:30 am 
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I may just put a cast iron manifold on the right side just so it won't glow. Normal or not it doesn't feel right to me knowing that that's going on under there.

Are there any further thoughts on the magnetized distributor theory? I noticed while performing the test that the timing jumps up at right around 1500 rpm. I have also noticed that the hesitation happens right around 1500 rpm. My theory is that intermittently the timing is not advancing as it should.
How can I watch what the ecm is doing with the spark while I'm driving? Is there a wire at the ecm that I could monitor with a DVOM? Or it this something that I could use WinALDL for?

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Fri Jun 26, 2009 12:33 pm 
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I did some research on exhaust gas temperatures. There are about a bizzilion different conditions that affect EGT. However, 1800 degrees is in the range of normal when the EGT probe is reading the temp within 1 inch of the exhaust port. On the subject of the "magnetized" dist, I've never heard of that condition. That certainly doesn't mean that it doesn't exist. I'd ask the person that told you about it to give you some technical info on that condition. My '96 had a serious "random misfire" condition. It set that code several times. While doing a tuneup I found that I could move the dist rotor sideways about 1/4 inch. The top bushing was worn to the extreme. I changed the dist with a good one and it has not set that code since. Something you should check. \:D/

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Sun Jun 28, 2009 8:04 pm 
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Thanks for doing that research on EGT. I also did some googling on stainless steel, I found that it will glow bright orange at around 1800 degrees F. So, maybe I just shouldn't worry about it.
As for the distributor question, the guy that told me about it doesn't know anything more about it. He had heard it from someone else a long time ago.
I just went out and checked my distributor for wear in that top bushing. There is zero side to side movement in the rotor.

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Sun Jul 05, 2009 3:51 am 
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The test that guy was having you check has to do with the centrifugal weights in the dist. Yes, as the engine spins faster the weights will move out advancing your timing. If they rust or spring become weak it will throw off your timing.

Visually inspect your pick up coil in the distributor. I've seen them look like they are cracking. This is breaking down internally and will cause bad miss fires and stalling. My dad's suburban was so bad it actually looked burned. Also connect an ohmmeter to both pickup coil wire terminals. The reading should be steady at one value within 500-1500 ohms. Also check to ground, You should be open to ground.

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 Post subject: Re: Quote of the day: "Why are the headers glowing?"
PostPosted: Mon Jul 06, 2009 7:37 am 
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James,

Just a quick question for you. What PROM chip do you have in your ECM?

I ask because I had a '87 Astro before & changed my PROM to the latest one & was very suprised by how much better it ran, shifted & had better fuel economy.

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