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bad sputtering and backfiring problems....

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Old 06-18-2008, 10:38 AM   #1
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Default bad sputtering and backfiring problems....

well my girl is gettin sick whenever i start her up she starts fine. then then rpms come down after the initial rev and flucuate from 600 rpm to about 900 rpm. when this is happening the oil pressure gauge jumps around randomly, but never goes below the red line at the bottom... now if i put my foot on the gas bringing the rpms up to about 1200 it will stay steady. if i dont warm it all the way up to normal running temp before i start driving it will backfire badly in second gear when im accelerating. it even backfired in 4th gear yesterday and even after it warmed up it backfired. im not sure whats going on, was wondering if anyone else has had this problem before. i put new plugs, wires, and distributor cap in it about a year ago. im guessing its not that. its frpp 9mm wires, oem plugs and msd cap. also im not sure if this is related but the other day i stoped suddenly and my car stalled, when it did the amp light and the check engine light came on. i restarted it and they both went off... anyways if anyone has any ideas what it could be im all ears... btw its an 88 gt with stock engine, either 330k miles or 230k, but the previous owner said it was rebuilt.... i dunno any help would be greatly appriciated... thank you
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Old 06-18-2008, 10:40 AM   #2
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Default RE: bad sputtering and backfiring problems....

I would check engine codes and do a cylinder balance test.
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Old 06-19-2008, 05:56 AM   #3
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Default RE: bad sputtering and backfiring problems....

the check engine light isnt on, so i dont know if any codes will pop up....
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Old 06-19-2008, 06:11 AM   #4
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Default RE: bad sputtering and backfiring problems....

I would clean the IAC first and check your TPS voltage
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Old 06-19-2008, 06:34 AM   #5
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Default RE: bad sputtering and backfiring problems....

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ORIGINAL: 8850gt

the check engine light isnt on, so i dont know if any codes will pop up....
The only way to find out is by running a DIY KOEO/KOER/Cylinder Balance Self-Test .... there are failure codes that will not cause the CEL to turn on, you should also verify the basic items...... fuel pressure, initial timing. Regarding the TPS..... if you don't have a TPS related failure, it's OK.... no need to adjust a non-adjustable sensor if the EEC sees it doesn't have a problem. LUK
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Old 06-19-2008, 11:19 AM   #6
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Default RE: bad sputtering and backfiring problems....

i guessing its a 1988

ther is no CEL on the 87 and 88s, there is no bulb in there from the factory...

run the KOEO KOER tests.
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Old 06-19-2008, 01:26 PM   #7
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Default RE: bad sputtering and backfiring problems....

88, speed density or converted to MAF? Mine was doing similar things and eventually found it to be vacuum related to the hose to the MAP being old and rotted. Mine was a pin hole leak and it made the car run like crap and misfire here and there and buck around. Replaced the hose and presto runs like a champ... well a ugly partially paint stripped, old rotted tires, ripped top champ anyway
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Old 06-19-2008, 01:38 PM   #8
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Default RE: bad sputtering and backfiring problems....

its converted to maf, how would i check for the vaccum leak? it only does it when i first start up, and it doesnt do it everytime. sometimes when i start it up, it runs fine... and sometimes its worse than other times...
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Old 06-19-2008, 01:45 PM   #9
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Default RE: bad sputtering and backfiring problems....

If its been converted clean IAC and MAF first, verify the spliced in pigtail wiring has not come loose. There are many ways to check a vac leak, everyone like something different. Professionals use smoke, some spray a shot of carb cleaner around suspected areas, I personally use a plumbers torch witha rubber hose.Iturn on the valve and move the end of the hose around the vacuum hoses and ports and listen for a change in the idle...
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Old 06-20-2008, 05:28 AM   #10
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Default RE: bad sputtering and backfiring problems....

ug, im not very good at doing this kind of troubleshooting think it would be a good idea to take it to my mechanic? just dont want him to give me alaundry list of stuff i dont really need to fix....
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Old 06-21-2008, 02:04 AM   #11
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Default RE: bad sputtering and backfiring problems....

Sounds like a bad IAT or coolant temp sensor to me if it's only doing it when cold.

The surging you're feeling when driving sounds to me like lean surging & generally what causes it when cold is either of those two sensors not working. If one isn't working the computer will read it like it's getting normal warm air in the engine. When the engines cold it will dump in more fuel to compensate for the air being more dense. Gasoline engines generally start surging around 16.6:1 a/f ratio.

as you know there's more air getting in your engine when it's cooler than when it's warmer, obviously the eec must tell the injectors to put more fuel in otherwise it will cause it to run lean.
Both can cause an eratic idle. If the bad idle persists after that, try cleaning the IAC.

As for location. The IAT is on the drivers side in the (i believe) #5 runner (the front driver side one) on the lower intake. Should have two wires coming out of it.
The coolant temp sensor for the EEC is on the passenger side. I believe the top tube of the two black tubes that go to the heater core. It'll be more toward the front of the engine.

Just to let you know there are two coolant temp sensors. The one on the passenger side like i described above is for the EEC only. The one wire one on the drivers side is for the gauge only & has nothing to do with the eec so don't worry about checking that one.

You can check both if you have a volt/olm meter. Here's an image to help you out.

Click the image to open in full size.

BTW, you can check both sensors when the engine is cold & not been running. As long as they have the correct cold reading. With the key off both should read around 20-30 ohms if the engine is cold (obviously this will vary depending on the outside temp, check the table above for reference)
Or you can check the voltage reading with the key in the on position.

Both sensors are very important for spark & fuel curves so either one could do it.

Hope this helps.
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Old 06-23-2008, 12:11 PM   #12
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Default RE: bad sputtering and backfiring problems....

well i took it to my mech. he looked under the hood and saw the vaccum hose from my maf to the sensor wasnt connected. it actually had a bolt in the end of the hose blocking it.... anyhow, once i took it for a test drive it ran great, not problems at all. so i head home, im turning my car off and nottice my check engine light is on now... but the car is running better than it did when it wasnt on... im supposed to take it back tom, to have them run codes on it. is there anyway i can run codes on it without the machine? any help would be appriciated ty
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Old 06-23-2008, 12:46 PM   #13
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Default RE: bad sputtering and backfiring problems....

Yeah you can run codes. You need to go back up to the top and actually read the link Joel5.0 posted. Its very easy to run the codes urself.
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Old 06-23-2008, 08:39 PM   #14
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Default RE: bad sputtering and backfiring problems....

i have no clue what he is talking about.... thats why i asked again
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Old 06-23-2008, 09:24 PM   #15
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Default RE: bad sputtering and backfiring problems....

http://myshifter.com/joel50/EECTEST.html

What part are you having trouble with?
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Old 06-24-2008, 06:36 AM   #16
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Default RE: bad sputtering and backfiring problems....

didnt realize it was a link, my bad
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Old 07-02-2008, 07:13 AM   #17
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Default RE: bad sputtering and backfiring problems....

ok so i took it too my mech, the codes returned a bad maf sensor, part number e7ef-9f479-a2a. i did a google search and couldnt find anything relevant.. its the peice that the hose plugs into, its on the firewall. anyways the guy told me to get a new one and see what happened. i havent had time to look for this part, was wondering if anyone knew the name of it so i could find it easier. also my car is running worse than ever on start up. also was wondering what IAC stood for. and what my tps voltage should be at. thanks for the help guys, i am greatly indebt to ya'll
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Old 07-08-2008, 08:34 AM   #18
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Default RE: bad sputtering and backfiring problems....

anyone able to help with the post above??? ty
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Old 10-17-2008, 06:32 AM   #19
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i think you mean map sensor not maf...
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Old 10-17-2008, 07:29 AM   #20
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Originally Posted by GT87Stang View Post
i think you mean map sensor not maf...
i second the opinion, there is no vac line to the maf, and also if the vac line to the map sensor was plug, it is because your converted to maf. its suppose to be this way, when you convert, you plug the map sensor vac line and leave the map sesor open so it can read the air temp of outside or something like that
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Old 10-17-2008, 07:29 AM
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