73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Chevy3+3 on October 06, 2013, 10:15:30 pm
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Since the weather is turning cooler and overnight lows getting in to 40's my truck the last few mornings has been backfiring out the exhaust pipes. It only lasts about 30 seconds and then the truck runs great the rest of the day. It never backfires again. If the overnight temps stay warmer then it doesn't backfire on start up.
Could it be an EGR problem or a coolant temp sensor problem causing it to run lean?
I just don't see how the cooloant could warm up in a matter of 30 seconds?
Any thoughts? Thanks
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We got a couple of things here. First if its back firing, generally that's to much unburned getting down the exhaust pipe meaning a rich condition. Secondly if the computer is "Faked out" thinking its to lean and creating a rich condition the next step is to start trouble shooting o2 sensor coolant sensor etc. If you need help with that let us know. There are a couple TBI Guru's on the site.....I'm not one of them.
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I found a broken vacuum tube that went to the Air Injection Valve ao I fixed that. I made sure the EGR valve was working properly and not stuck. I also replaced the coolant temo sensor on the intake. I then fired the truck up and the backfiring remains but once again it stopped after after 30 seconds.
I then got some carb cleaner and started spraying the throttle body base gasket and spacer gasket. I found that when I sprayed it on the passenger side the engine bogged some and/or slowed down. So I clearly have a TBI gasket leak. I think that might be my problem.
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Keep us informed with what you find.
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Keep us informed with what you find.
x2 30 seconds may be all it takes for the gasket to expand from the heat enough to run fairly decent...
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Sounds good, be wary of buying and "throwing parts" at the problem. Keep your money in your pocket, there is a way to troubleshoot everything on your motor with enough patience you'll get to the bottom of the problem. There's a lot of smart people on this site. Good Luck!!
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Well I replaced the TBI gasket between the spacer and the intake manifold. Once I got it removed I could clearly see where it had been leaking. I put it back together and started the truck. It only backfired or popped about 4 times. Definately not as long as the previous mornings. I wonder if the TBI needed to retune since I got rid of the vacuum leak through the TBI base plate.
I hope it fixes it but I'm sure I cant be that lucky
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What other vacuum leaks might you have? Hoses all OK? Power steering booster diaphragm OK? No unused open vacuum ports?
Like you say, though, could just be that the ECM will have to re-learn the car.
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All those vacuum hoses appear to be hooked up and not leaking. I will know shortly if it going to backfire. Getting ready to go start it for the morning
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Well unfortunately my popping & backfire still remains. It backfired about 5-6 times this morning in a time frame of 20 seconds or so. Even after it stops popping if I get into the throttle it seems to stumble just a little like its clearing it throat. I checked exhaust when it was clearing out and it was a little black telling me its a little rich or had loaded up a little.
Could my timing being off a little off affect it only when its cold out? I'm almost sure it is something simple but hard to figure out the simple things sometimes
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Well, if the mixture is wrong on a TBI, it seems to me it is either the 1) sensors, 2) ecm, or 3) injector(s). The most likely remaining culprit here is probably the O2 sensor; you already changed the coolant temp sensor. Not sure how to troubleshoot the O2 sensor. Anybody know if the O2 sensor for this setup has a heater circuit? If that's out, the O2 sensor will read wrong until the exhaust gases bring it up to temp. How many wires does your O2 sensor have?
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Here are a few things to check:
- Does the SES light come on with ignition?
- Are there any codes?
- Check the fuel pressure.
- Remove the air cleaner and wipe off the tips of the injectors with a rag. Turn the ignition ON, but do not crank the engine. Do you hear the fuel pump run for about 20 seconds? Check the injector tips for fuel - they should be dry. Repeat this cycle 2 - 3 times. Injector tips should remain dry.
- Refer to the factory manual and check the operation of the Air Management Valve and air injection system - on a cold start it should inject air into the exhaust for about 30 seconds or so to heat the cat.
- Check the MAP and TPS functions.
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Here's something you might try. When you start the engine cold, turn the ignition on, but do not start it for 60 seconds. Put your seat belt on, check your mirrors, light a cigar, whatever. That'll let the fuel come up to full pressure and the O2 sensor heat up. Then start it and see if it acts the same. If that fixes it, you can then see how long you need to leave it on before you start it. Maybe it only needs thirty seconds to get itself ready.
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The truck only has 1 O2 sensor that I can find and it on the drivers side manifold. It only has 1 wire to it. The truck only shows the SES light when the switch is on and the truck not running.
After the truck is done popping then it runs great. Its gotta be fuel & air related I think
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Well I'm not sure what to try next. I think I have exhausted myslef looking for vacuum leaks. If I had a decent vacuum lesk I think I would see it run bad even when warm. But this still only remains on the first start up of the day when the outside air temp is cooler. So in my mind it has gotta be either the cool intake air, the coolant temp sensor (which I already replaced) or another sensor whos duties are involved with cold starts (choked starts for colder weather).
I will try and turn key on in morning and leave sit about 60 seconds before cranking and see if there is any change.
I forgot to mention that on a cold start. It starts and idles up like it should and then within 5-10 seconds is when the popping starts. It then only lasts about 20 seconds. The colder it is the longer it lasts.
Today after it was warmed up the RPMs were 1000 when idling and today was 75-80 degrees. Seemed a little high to me but may be normal.
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Well this morning I turned on the ignition and let it sit for about 60 seconds before cranking it. After it fired up I was waiting for the usual backfires to start but to my suprise......it never backfired. Last nights low temp was only 55 degrees so it may have not been cold enough and may be why it didn't backfire.
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So that may be it. Full pressure to the fuel rail and O2 sensor to temp.
Or it may have just been too warm overnight to have the problem.
Keep us posted.
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I am the guy that had the backfiring problem on an 88' Chevy Crew w/454 TBI 4x4 Dually only when the overnight low temps were in the 40's or below. Truck has 130k miles and doesnt use coolant and doesnt burn oil. Since then I have remedied several small issues and changed a few parts but I still have a problem. My fuel mileage is roughly 8-9 MPG normal driving and highway speeds of 55mph. At 55 my engine RPM is about 2400-2500. I have no Service Engine light on after the truck is started.
I believe I am running to rich when the overnight temps get in the 40's. I would get intermittent backfiring for about 20-30 seconds and then the truck would clear up and run smooth the rest of the day. When started the truck idles up to about 1200 RPMs when cold. When warm it idles about 1000 RPMs and about 700 RPM in gear when warm. These RPMs appear to be normal.
Here is a list of what I have done:
1. Replaced the Coolant Temp Sensor
2. Double checked that the EGR valve is working correctly
3. Found and fixed all the vacuum leaks (including replacing TBI baseplate gasket)
4. Checked timing (bypass wire unplugged) and found it was set at 0 BTDC
5. Set initial timing at 4-5 degrees BTDC (bypass wire unplugged)
6. Unhooked battery for a few minutes, plugged bypass wire back in and hooked battery back up.
When I started the truck this morning with a 45 degree outside temp the truck fired up and after about 5 seconds of ignition the truck started popping/backfiring a few times. It did not do it as long as usually. I walked back to the tail pipe and it smelled a VERY strong fuel odor. I almost think it might be running to rich.
I do have a cracked passenger side exhaust manifold. I have a new replacement and plan to install it within the next few days although I do not believe this to be the reason I am backfiring.
I believe something is telling my TBI to dump more fuel causing me to run rich when cold and potentially even when warm. Should I or would it be in my best interest to replace the O2 sensor? There is only one O2 sensor and it is located on the drivers side exhaust manifold and is hooked up with a single wire.
I have also thought about checking/resetting the valve clearance or preload making sure they are correct.
Any thoughts or advice would be greatly appreciated. Thanks
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have you check the ECM to see if its throwing any codes? I'm sure that would help alot..
maybe take it down to a local parts store and have them check for codes.
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What is...Cracked exhaust manifold for 500 Bob. I've seen where they cause lean condition in cold a weather
What's under the hood??? If you have to ask maybe we shouldn't race...
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have you check the ECM to see if its throwing any codes? I'm sure that would help alot..
maybe take it down to a local parts store and have them check for codes.
I was under the impression that as long as I didnt have any SES light on the dash then I wouldn't show any codes?
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What is...Cracked exhaust manifold for 500 Bob. I've seen where they cause lean condition in cold a weather
What's under the hood??? If you have to ask maybe we shouldn't race...
Can you elaborate? Are you saying that possibly the cracked manifold is showing the ECM a lean condition causing it to deliver more fuel than necessary?
Thanks
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have you check the ECM to see if its throwing any codes? I'm sure that would help alot..
maybe take it down to a local parts store and have them check for codes.
I was under the impression that as long as I didnt have any SES light on the dash then I wouldn't show any codes?
honestly, your guess is as good as mine lol. im not great when it comes to EFI or TBI. But since most places do it for free i figured why not.
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I was under the impression that as long as I didnt have any SES light on the dash then I wouldn't show any codes?
The SES light illuminates when a detectable problem occurs, then typically remains lit until the ignition is cycled Off. Any resulting trouble codes are stored in the ECM memory for subsequent retrieval. If the problem doesn't recur within a certain number of ignition On-Off cycles, the code is automatically purged from memory. So, if there has been any recent 'code' activity, a trouble code may be stored.
However, a complication can occur that muddles efficient diagnosis if any monitored sensors have been unplugged while the ignition was switched On, setting false codes. Therefore, the best approach is to: 1) retrieve any existing codes and write them down, 2) clear the ECM memory by removing the ECM-B fuse or disconnecting the battery for 20+ seconds, then 3) drive the vehicle normally to see if any new codes occur.
Can you elaborate? Are you saying that possibly the cracked manifold is showing the ECM a lean condition causing it to deliver more fuel than necessary?
An exhaust leak can allow fresh air to be drawn into the exhaust stream. If the leak occurs ahead of the O2 sensor, the sensor will register the added air; the ECM will interpret the O2 signal as a lean condition and command extra fuel, causing the engine to run rich. However, an O2 sensor must be above a temperature threshold of ~600-650° F in order to function correctly. Hence, O2 sensor output is ignored by the ECM during cold startup, until the sensor is sufficiently heated by the exhaust flow. Later model 4-wire O2 sensors have special integrated heating elements that bring the sensors up to temperature rapidly, but your single-wire sensor doesn't have that attribute. So, the O2 sensor is not likely an issue for you.
First, fix the exhaust leak. Then you are back to a prior post...
- What does the fuel pressure measure?
- Are there any stored trouble codes?
- Remove the air cleaner and wipe off the tips of the injectors with a rag. Turn the ignition ON, but do not crank the engine. Do you hear the fuel pump run for about 20 seconds? Check the injector tips for fuel - they should be dry. Repeat this cycle 2 - 3 times. Injector tips should remain dry. This step determines whether the injectors are leaking fuel.
- Refer to the factory manual and check the operation of the Air Management (aka: Diverter) Valve and air injection system - on a cold start it should inject air into the exhaust for about 30 seconds or so to heat the cat.
- Check the MAP and TPS functions using a voltmeter. You'll need a voltage vs vacuum chart for the MAP. Regarding the TPS, you're mostly interested in the throttle closed voltage (~0.56 v) and a smooth voltage transition to full throttle (< 5 volts).
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Thanks BD! I couldn't respond in time
What's under the hood??? If you have to ask maybe we shouldn't race...
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Thanks BD. My exhaust manifold crack is after the O2 sensor. I drip tested the injectors and they appear to remain dry. They also spray an even cone pattern and I see no drips I from injector while running.
What's controls the fuel & air mixture when the ECM bypasses the O2 sensor? From what you said above it is almost as if once the O2 sensor get heated up then it stops backfiring.
I also wanted to ask what would happen if the Coolant temp sensor was unplugged? Would this cause an full time rich condition or lean condition.
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I just fixed my header collector gasket leak and all I can say us wow I was losing a lot of power. It also caused miss fires at idle and during driving.
What's under the hood??? If you have to ask maybe we shouldn't race...
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I just fixed my header collector gasket leak and all I can say us wow I was losing a lot of power. It also caused miss fires at idle and during driving.
What's under the hood??? If you have to ask maybe we shouldn't race...
Well tomorrow I will try and resolve all my exhaust leaks. I have exhaust manifold to replace and a flange gasket on the other manifold to replace
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Hope this helps you out.
What's under the hood??? If you have to ask maybe we shouldn't race...
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Thanks BD. My exhaust manifold crack is after the O2 sensor. I drip tested the injectors and they appear to remain dry. They also spray an even cone pattern and I see no drips I from injector while running.
What controls the fuel & air mixture when the ECM bypasses the O2 sensor? From what you said above it is almost as if once the O2 sensor get heated up then it stops backfiring.
I also wanted to ask what would happen if the Coolant temp sensor was unplugged? Would this cause an full time rich condition or lean condition.
The ECM applies a constant ~0.45 volt across the O2 sensor. The O2 sensor is designed to modify that ECM voltage. But, until the O2 sensor reaches >600° F, its effect is null and ECM O2 voltage remains constant at 0.45 volt - and the ECM operates in "Open Loop." Essentially, Open Loop is a program condition that simply excludes O2 sensor output, while monitoring CTS, MAP, TPS and Tach to adjust fuel and timing. However, once the O2 reaches >600° F, it modulates the fixed 0.45-v ECM signal between ~0.1 v (lean) and ~0.99 v (rich), causing the ECM to enter "Closed Loop." Closed Loop operation incorporates the O2 sensor output to tightly control fuel delivery for a 14.7:1 air-fuel mixture.
The CTS varies its resistance from 100,700 Ω (-40° F), to 13,500 Ω (20° F), to 7,500 Ω (40° F), to 185 Ω (210° F). In other words, very high resistance when cold. Unplugging the CTS would force fuel enrichment along with an illuminated SES lamp and code 15.
Correct the exhaust leak then continue from there. Now, would also be a good time to check the spark plugs, cap, rotor, and plug wires, if you haven't done so already.
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Check the MAP sensor and the connections to it. Without the O2 sensor on-line, that will determine your mixture.
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i want to get on this post also. soooo, do you have your heat riser pipe still installed?
did you check timing?
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Heat riser pipe is still installed. Everything is bone stock under the hood. I need to fix exhaust leaks first and go from there I guess. I just set the initial timing to around 5 degrees BTDC.
The dizzy cap is an MSD and the plug wires are 8.5mm and appear to be new and high quality. I think the previous owner put them on trying to resolve the same backfiring problem. I just bought this truck and this morning backfiring is the only thing left to fix.
I greatpy appreciate all the help and wealth of knowledge some of you bring and share here. I am a very mechanical guy but sensors and electronics are a little out of my element.
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you "just" set the timing? when? not doubting your skills but you did connect the tan/black wire before setting timing at ot?
i know you siad you replaced the cts but if you have a used one in another truck i would swap them out or just replace yous again. heck i just bought a ckps from a dealer for $100 when i could buy autozones for $40. sometimes they are bad right out of the box
could try to test it also
212°f 177 ohms
194°f 241
176°f 332
158°f 467
140°f 667
122°f 973
113°f 1188
104°f 1459
95°f 1802
86°f 2238
77°f 2796
68°f 3520
59°f 4450
50°f 5670
41°f 7280
32°f 9420
23°f 12300
14°f 16180
5°f 21450
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Okay well a little update. I got the passenger side exhaust manifold replaced and the gasket was blown. Both flange gaskets were leaking also. The spark plugs were crap. Someone installed Bosch platinums and that was a bad choice. I replace the plugs with AC Delcos and replaced cap, rotor and wires also. After changing everything listed ablve I still have an exhaust leak. I hoped the drivers side manifold gasket wasn't blown but it apparently is.
Since I have a fuel mixfure issue and run a little rich at all timez I bet the drivers side gasket being blown is allowing aire to be drawn in before the O2 sensor causing a lean reading and therfore causing the TBI to dump excessige fuel.
As for the timing. I got thr truck to operating temp and then unplugged the brown wire with black stripe. After doing so the timing light showed the timing to be set at 0 degrees. A big block is to be set at 4 degrees BTDC. I set it on about 5 degrees BTDC. I then shut the truck off. Unhooked battery cable and plugged bypass wire back together. Then hooked up the battery and proceeded to start the truck. Let me say what a difference it made having the timing set properly. Itruns so much better now. The motor feels more responsive and smoother.
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Glad to hear all is going well. After that next gasket you'll be even more happy...
What's under the hood??? If you have to ask maybe we shouldn't race...
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Well I just finished replacing my drivers side exhaust manifold gasket. There wasn't a lot left of it. The truck is runningso much better. Who would have thought exhaust leaks could cause so many issues.
Now I need a cooler morning and see if she backfires on a cold start up.
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I believe the term its reversion. Cold air being drawn back into the cylinder causes it. I'm searching for some good header gaskets now. Mine keep telling me to shhh lol
What's under the hood??? If you have to ask maybe we shouldn't race...
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...Now I need a cooler morning and see if she backfires on a cold start up.
They'll be upon us soon enough....
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I believe the term its reversion. Cold air being drawn back into the cylinder causes it. I'm searching for some good header gaskets now. Mine keep telling me to shhh lol
What's under the hood??? If you have to ask maybe we shouldn't race...
I bought some years ago that were Mr. Gasket. They were around $18 for a set i think. They were black with some blue print on them. I used those with some good header bolts and never had another problem for many miles and several years.
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I'm gong to look into those thanks. Glad to hear its running better
What's under the hood??? If you have to ask maybe we shouldn't race...
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Well it was officially cold enough early this morning I got to try a cold start up. I was pretty nervous and hoped I had solved the backfiring issue. I cranked the key over and she fired up and ran smooth and no backfiring. No I can concentrate on other things. My 2.5" lift will be here today but probably won't have time to intall it until next week sometime. I also think I am gonna throw a Flowmaster Super 44 muffler on it. I don't drive it everyday and I am still young enough I don't mind hearing a little noise out the back.
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That's what I'm takin bout :-)
What's under the hood??? If you have to ask maybe we shouldn't race...
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>Chevy3+3
Rave congratulations on your success!!!
>454Man
You may want to look into the Felpro 1404 (http://www.summitracing.com/parts/fel-1404/overview/) for your exhaust, as well.
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Thanks bd.
What's under the hood??? If you have to ask maybe we shouldn't race...