Miss firing - Team Camaro Tech
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post #1 of 16 (permalink) Old Jun 26th, 11, 02:25 PM Thread Starter
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Miss firing

I am looking for a bit of guidance to trouble shoot a 1998 RS with a 3800 auto.
The engine starts and runs with a miss in it. I have red that this engine is prone to some of this.
When I checked the coolant was very low and radiator had rust trace on the filler neck.
The missing is through the whole throtle range and check engine light is on as is the ABS light.
I will be getting the manual for this car this week but wanted to get a feel for what the commun problems are with this 3800.
I cant hear any noise coming fom the open radiator so i am assuming that no head gaskets are gone.
Thanks for the help.
Sarah
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post #2 of 16 (permalink) Old Jun 26th, 11, 06:04 PM
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Re: Miss firing

It could be anything from a broken coil pack, each pack ignites two cylinders, to a broken plug wire and to include a fouled spark plug. A cylinder not firing will give a rich fuel mixture and the O2 sensors are picking up this event and triggering the MIL light.

Advance Auto will let you borrow a code reader to plug into the diagnostic connector under the dash to pick out the diagnostic code for the fault(s).

Good point in getting a manual to show you how to troubleshoot the problem.

The rust traces at the filler neck could be from regular water being poured into the radiator. You won't hear noises, but, you would see bubbles if a head gasket was blown, maybe, not all the time. Check oil level dipstick to hopefully not see any water in the oil as evidence would show a milky solution and/or a higher level than normal of fluid.

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post #3 of 16 (permalink) Old Jun 27th, 11, 04:47 AM Thread Starter
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Re: Miss firing

Thank you everet,
I was thinking along the same lines as a plug or wire, I have never worked with the coil packs yet and did not know if they went bad.
As for the codes i will get the manual and see how to pull that as i did on my old truch with the lights, unless of course the 98 wont let you do that.
Then il have to look at what the ABS light being on might be.
I figure these Forums are a good place to start since there is sutch a vast experience base already here.
Thank you for your reply
Sarah
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post #4 of 16 (permalink) Old Jun 27th, 11, 05:58 AM
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Re: Miss firing

Your car is OBD2 compliant, use the code reader to start.
Coil packs do go bad. They are two coils in one package plugging into a board for input from the PCM.

ABS light is another circuit and could be something as simple as low fluid in reservior.

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post #5 of 16 (permalink) Old Jun 30th, 11, 11:18 PM
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Re: Miss firing

dist in front---water leaking from water pump onto dist --need to replace water pump and dist
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post #6 of 16 (permalink) Old Jul 3rd, 11, 10:54 AM Thread Starter
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Re: Miss firing

not a V8 so its not the dist.
its a 3800 and i do have a reader on the way to plug in.
should it fail il start pulling plug wires to see what cyl is missing
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post #7 of 16 (permalink) Old Jul 3rd, 11, 01:48 PM
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Re: Miss firing

Quote:
Originally Posted by sarah01 View Post
should it fail il start pulling plug wires to see what cyl is missing
No, it should not. Pull a plug and the cylinder not making a change in rpm is the faulty one.

You could do the same test with a timing light and check for spark; if light lights, good cylinder/coil for the cylinder tested.

You find the faulty cylinder, swap the coil pack with another and see if trouble follows the coil. If it does, bad coil. If it does not, bad ign module, the item the coils plug into.

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post #8 of 16 (permalink) Old Jul 5th, 11, 12:39 PM Thread Starter
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Re: Miss firing

The car will be in my driveway tomorrow so it will be easier to trouble shoot.
I did pull the codes from the OBD today, I got a 114, 144 and a 300.
The 300 is coverd as missfires in the manual (haynes) but the other 2 arnt.
closes one is the 114 and it relates to the coolant sencor, since the rad is very low it could be it.
the other indicates O2 sencor heater.
The last 2 are from the generic manual that came with the manual.
I start pulling plugs and moving parts tomorrow.
Thanks for any input any one has.

Sarah
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post #9 of 16 (permalink) Old Jul 5th, 11, 07:07 PM
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Re: Miss firing

Make sure of the first two characters of the DTC (diagnostic trouble code), ie, P(zero)XXX, meaning Powertrain(P), generic(0) followed by the definition.

P0114 would be IAT sensor 1 circuit intermittent = Intake air temperature sensor ckt could be a corroded connection or dirty sensor in the mass air flow sensor, if equipped with MAF or if Speed Density type EFI, a separate temp sensor in the air cleaner, or commonly placed in the intake manifold. Or a faulty sensor internally. Might even be a lack of reference voltage from the PCM, generally, +5 volts from the PCM and a reduced return voltage back to the PCM for monitoring.

P0144 would be O2 Sensor circuit high voltage. A broken internal sensor or since engine is misfiring, a high voltage output due to a rich mixture detected. I would consider this a secondary DTC.

P0300 would be as you suggest, random/multiple cyl misfire. Could be anything for any reason, bad coil, plug wire, spark plug, faulty injector, etc.

If you believe O2 sensor heater circuit, find the O2 sensor in the engine diagram and follow backwards its heater power from the power distribution, generally from a relay generally controlled by the PCM and/or fusible link or fuse and check to see if sensor is getting heater voltage and make sure sensor body has a good ground for completing the circuit. If there is power and a return, but no heat still, you can check the resistance of the heater coil by unplugging the connector and checking resistance of the heater through the sensor harness, should be a few ohms, not an open.

The input sensors get a reference voltage from the PCM, as said, +5 volts, and the PCM reads the return voltage. Depending upon the return voltage amount, it tells the PCM the condition of the operating engine. Example: coolant sensor - ambient temp or colder, resistance within sensor is high, above 5000 ohms. PCM reads a small amount of voltage through the circuit, cross references to a cold engine, the PCM increases the injector pulse to richen the mixture - makes injector open longer, as in closing the choke plate on a carburetor. As coolant heats up, sensor resistance goes down, generally to below 200 ohms, more voltage returns, injector pulse shortens in time decreasing the volume of fuel. By Federal mandate, engine has to be at the federal emissions spec after 90 seconds - read 'choke open' or out of enrichment mode - thus, PCM reads the O2 sensor - has to be heated by now, above 600°F, and PCM goes into 'closed loop mode' reading sensor output. MAF circuit reads the current drawn, ie, heated sensor wire by the PCM. More air drawn across the single strand of wire, more current given to keep wire heated. Current amount increase meaning more air is used, more fuel needed, so on and so on.

The PCM workings, EFI, can take volumes to explain, but hopefully, the above explanation will give some insight to your problem. This in ONLY the very top of the iceberg, about the first foot at the peak. The Haynes manual does explain the sensors function, but due to print space, is vague. Haynes does print a EFI manual explaining all EFI configurations and the differences between them.

Good luck. Think before executing.

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post #10 of 16 (permalink) Old Jul 6th, 11, 06:01 AM Thread Starter
Sarah
 
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Thumbs up Re: Miss firing

Thank you so much.
It mirrors what i have red in the manual and makes sense.
The car will be home today and I will start taking readings tonight or tomorrow morning after work.
Good advise, think before executing, wish my techs would do that once in a while.
So an other fun project begins and who know what I will learn, expectations are a running RS for under 2 K.

I will keep you posted.

Thank you very much.
Sarah
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post #11 of 16 (permalink) Old Jul 11th, 11, 07:26 AM Thread Starter
Sarah
 
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Re: Miss firing

I got a bit of trouble shooting done.
The O2 fault never came back after i cleared it nor did the IAT one.
I am left with the P0300 code.
I have a HEI test plug coming as well as a compression gage.
I did a priliminary check of the ignition using a timing light on every cylinder and found that all cylinders are missing at some point, from start up to engine warm.
I did find a page that walks through the steps of checking the coils, ICM and crank position sensors.
As well as injectors.
I will pull the plugs today and at least get an idea of what they look like
So far i belive it is ignition related by using the timing light to confirm the intermitent spark.
Please correct me if i go in the wrong dirrection.
Thank you for the help.
Sarah
1979 Yamahe XS 650
1998 Camaro RS
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post #12 of 16 (permalink) Old Jul 11th, 11, 08:36 AM
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Re: Miss firing

Quote:
Originally Posted by sarah01 View Post
I did a priliminary check of the ignition using a timing light on every cylinder and found that all cylinders are missing at some point, from start up to engine warm.
I did find a page that walks through the steps of checking the coils, ICM and crank position sensors.
If ALL cylinders are misfiring, it would lead me to believe either the ign module, what the coils plug into, or the crank sensor is bad.

Good test using the timing light.

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post #13 of 16 (permalink) Old Jul 11th, 11, 08:40 PM
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Re: Miss firing

i agree with everett-
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post #14 of 16 (permalink) Old Jul 20th, 11, 07:28 AM Thread Starter
Sarah
 
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Re: Miss firing

Time to close this loop.
I did fing one coil pack that had the secondary windings open, an other that had 23K ohms through it and the last red the normal 5 to 6 K.
I got 3 MSD coil packs on it now and it rune like a kitten.
Next issue with this car is the ABS inop light on and brake in the dash.
Off i go to look for more info.
Thank you for all the leads on this trouble.

Sarah
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post #15 of 16 (permalink) Old Jul 20th, 11, 09:23 AM
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Re: Miss firing

Cool!

ABS & BRAKE light on could mean blown stop light fuse.

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