2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

something stuck? Bad Backfire

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Old Jun 25, 2011 | 10:17 AM
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amondchristopher's Avatar
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From: indianapolis
something stuck? Bad Backfire

Gettin ready for a move , my 7 is fn up ..


is starts up fine gets to normal op. temp thin idel goes to crap adjusted tps to 1 volt no change to runabilty .
took out for a spin ran ok but under de-accel backfire BAD backfire like shootin a spud gun i thought my muff blown up . throttle it out and thin **** started happenin sounded like lawn mower if i hit gas it would sputter not increase rpm. i could hold rpm and it sounded ok engage clutch back to mowing lawns lol..... this would come and go like something was stuck but i dont know. i barely made it home. thought i blown motor but i go so start next day it fires up ok runs like normal sounds like normal WTF. dont want this to happen again. i have not done compression check but removed lower plugs cranked motor and it sounded like 3 even woosh on both rotors .
emissions are removed btw hard to start back up when motor is warmed up


here is sone things i have checked
TPS = 1volt whan warmed up
BAC made some clicking noises is that normal
Broke a air bypass valve see pic below and where can i find 1 ??
new injectors new gaskets for intake
idel still sucks *** but have not messed with
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Old Jun 25, 2011 | 10:19 AM
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pic of part i broke wires off
Attached Thumbnails something stuck? Bad Backfire-downsize.jpg  
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Old Jun 25, 2011 | 10:33 AM
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I may be wrong but i think that part has to do with the accelerated warmup system. I THINK I had one that was broken in the same exact spot. I cant remember if it affected how the car ran though.
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Old Jun 25, 2011 | 10:53 AM
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The part w/the frayed wire is the Air Bypass Valve as previously noted. Its job is to create the high rev warm up on a cold engine. Other than that it doesn't really serve much purpose. Are you driving the car w/the component removed from the engine and if so what did you do w/the open ended hoses which connected to it?
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Old Jun 25, 2011 | 11:48 AM
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Wow i read OP post wrong, i thought he was asking what it was not where to find it. I believe i found mine on ebay for like 10 bucks.
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Old Jun 25, 2011 | 02:38 PM
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the Air Bypass Valve is still in the car w/ the 2 hoses hooked up. question is why so difficult to start when motor is warmed and how can i can i solve the bad backfire probelms. and why it was stalling under throttle and NOT sounding Right (exhaust) and let me describe sound i have duel Greddy exhaust its LOUD!! this sounded like a lawn mower. still could hold rev but could not accel.
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Old Jun 25, 2011 | 03:19 PM
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Originally Posted by amondchristopher
the Air Bypass Valve is still in the car w/ the 2 hoses hooked up. question is why so difficult to start when motor is warmed and how can i can i solve the bad backfire probelms. and why it was stalling under throttle and NOT sounding Right (exhaust) and let me describe sound i have duel Greddy exhaust its LOUD!! this sounded like a lawn mower. still could hold rev but could not accel.
The high rev cold start enacted by the car doesn't come into play concerning warm engines so the Air Bypass is not your problem. Even if the bypass valve was disconnected and the car was started cold the high rev start would still occur because the BAC is involved. Problems related to a warm start "could" be related to the Water Thermosensor which helps to govern the necessary fuel needed to start the car. Colder car more gas, warm car less gas, but if not working properly you could have too much gas injected upon startup basically only if the Thermosensor had a low voltage reading being sent to the ECU. If the pin at the ECU for the sensor read high then either the car would see a warm engine and not try to flood it or the ECU would default to a warm engine scenario and do the same thing such as inject little fuel and not a bunch which occurs on a cold start.

Sometimes a lawnmower sound is cause by the engine running on "one rotor" among other things.

As stated earlier, the car conking out could be a ground problem. For example, the Main Relay has a ground. If that ground is poor it could cause the relay to shut off which would then cut power to the coils, injectors, ECU, etc....
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Old Jun 25, 2011 | 09:30 PM
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I'd start with the water temp sensor and check your grounds.
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Old Jun 26, 2011 | 10:45 AM
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water thermo sens. is new just replaced like a week ago . Grounds.... i have cleaned up the grounds under intake .. the 4 or so by the driver side shock tower andgrounded the boost sensor .... BUT thin again before i added the ground to boost senor i grounded the ref wire (wrong wire) rookie mistake that may messsed something else up .

a BAC question this thing should not make a buzzing noise (like stuck) tryed to clean thin noticed it making noise ... open and closed that is the operation of the componet correct ?? checked res. a while ago it was in spec.

BTW no codes are flashing from ecu
Thanks again for ever1s help
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Old Jun 26, 2011 | 11:11 AM
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Originally Posted by amondchristopher
water thermo sens. is new just replaced like a week ago . Grounds.... i have cleaned up the grounds under intake .. the 4 or so by the driver side shock tower andgrounded the boost sensor .... BUT thin again before i added the ground to boost senor i grounded the ref wire (wrong wire) rookie mistake that may messsed something else up .

a BAC question this thing should not make a buzzing noise (like stuck) tryed to clean thin noticed it making noise ... open and closed that is the operation of the componet correct ?? checked res. a while ago it was in spec.

BTW no codes are flashing from ecu
Thanks again for ever1s help
Problematic Thermosensors are usually a product of "faulty wiring" and not the component itself such that you will not know if the sensor and its wiring is doing its job "unless" you check the readings at the ECU pin related to the sensor which is pin 2I, Green/White wire. As the neverending story goes, 1 to 3 volts w/key to on with a cold engine, and .4 volts with the engine at its warmest.

As far as the BAC goes I believe you need to be careful as far as which terminal on the BAC receives voltage and which receives ground for mixing them up can damage it. If the terminals were wired correctly for testing purposes the solenoid will click. In this case the positive terminal is the one in which the B/W wire was connected to before disconnection of the plug. When mounted on the car after driving the car it should vibrate for a while before turning off.
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