Smog Time again

Shal

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Smog time here in California.

15mph/25mph test - tester couldn’t maintain consistent RPM during 25mph under load test.

He said there’s a misfire.

While driving back home, coming to a stop the idle started dipping to zero and engine would shutoff.

Plugs changed with Champion copper plus 2 weeks ago, o2 sensors changed since they were to original. Wires, PCV valve changed 2 years ago. Coolant changed 2 years ago.

1994 RT/10 stock. 55k miles.

Please help.
 
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Shal

Shal

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No codes when checking with key on off routine. Just code 12 since the battery is new.
 

GTS Dean

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I'm thinking you might have an intake gasket leak, throttle cables out of synch, or IAC pintle may be sticky. How old are your plug wires?
 
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Shal

Shal

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Plug wires changed 2 years ago. Plugs changed again this month.

How do I test an intake gasket leak?

Thank you for your responses
 
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Shal

Shal

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Would K&N filters mess up the IAC?

I resynched the Throttle cables.

Wondering if it’s ignition coils.
 

daveg

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First thought for me was coil.
To test Intake leak, spray small amount of starter fluid where intake meets head (up and down on both sides), if the idle picks up, that's where your intake leak is. Look at all vacuum hoses as well. Could also be bad injector(s).

PS, if you can find someone with a proper ODBI Scan tool, that would help.
 
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Goggles Pizano

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Search the forums. This exact situation (I also think it was in CA too) was asked. We when into tire sizes and bunch of other things as rpm/mph was off.
 
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Shal

Shal

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Tried using a timing light with tachometer to see if I can spot a ignition misfire... interestingly every other cylinder registers twice the rpm. Is that normal for a wasted spark system ?
 

Siciliano15

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dam they make u do smog in california even if the car is 30 years old?? i knew it was bad out there but i thought they had to at least have some cutoff point. that is crazy. id just move the hell outta that communist state. how do they expect people with cars that old to be able to pass tests designed for new cars?
 

MoparMap

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How often do you drive the car? Wondering if it might just need a bit of an "Italian tune up" with some highway driving for extended periods to clean things out. Though if you need to pass to drive it that becomes a chicken and egg problem. My mom's 94 had a bad coil a while back that gave her a nasty misfire, so not out of the question. I was able to use my DRB III to individually fire the cylinders and watch for spark, though you could do it the old fashioned way of pulling a plug and holding it against something while cranking the engine over (preferably with the fuel pump fuse pulled or something so you don't flood it). Sounds like you have some amount of spark though if you're seeing hits with a timing light. Sticky injectors would probably be my second guess, but those are a bit harder to isolate and test shy of just removing them and sending them somewhere for a cleaning. A bottle of Techron and a nice drive to use up a tank of gas can sometimes fix that though.
 

GTSnake

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If it's new plugs and wires the only other components in the ignition is coil and engine management. Swap out the plugs and see if the misfire changes cylinders to rule out plugs. Then switch wires and do the same thing. Then you can narrow down the component.
 
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Shal

Shal

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Thank you to all of you.

Re-Sync’d throttle bodies again. Took it to my only trusted mechanic. He cleaned throttle bodies, injectors. And smog passed without issues.

Slowly learning that with all the regular work, I need to routinely attend to the beast.

Mechanic even fixed the reverse light and 3rd brake light that never worked in 20 years of ownership.

Great to have a good Mechanic. I wish it was the same with Dentists. (No offense to anyone who is a dentist).
 

Goggles Pizano

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so how does it work? is there any cutoff at all? what if you have a car from the 80s or even the 70s do all of those need to be emission tested too?
Age of car that is a cut off from testing and type of smog test is state dependent and was continuously revised through the years.

Some states started with dyno smoging then switched to just OBD2 when data showed the OBD2 was very good and enough as a dyno machine was over $100-200k to buy and the state and county set the testing fee around $50. Not a great ROI for the garage as you did not need to get the car fixed there.

The COx, NOx, HC, etc ppm limits are adjusted as the vehicle ages. The ppm limits for a 15 year old are not the same as a 9 year old even if they are exactly the same.
 

Siciliano15

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I was more just curious about CA i know the other states all have their different laws with many states having no checks at all. i was just wondering if in CA if there is any cutoff at all or if all cars have to be tested. seeing that the OP has a car thats 30 years old and still needs testing thats pretty crazy.
 

redtanrt10

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I was more just curious about CA i know the other states all have their different laws with many states having no checks at all. i was just wondering if in CA if there is any cutoff at all or if all cars have to be tested. seeing that the OP has a car thats 30 years old and still needs testing thats pretty crazy.


1975 model year or older is exempt. You either learn to deal with it or get your car registered out of state. If you car runs good, it will pass. My '94 RT/10 has headers, cat back, K&N and passes every 2 years. Only issue I have is having to keep the RPM's in a 50 RPM band for 15 seconds, the local tech I use knows how to get around the usual monitor grounding (which isn't exacting) and gets the signal from my plug wires directly.

2000 and new cars only use the OBD test, plus gas cap test and visual. So his and my '94 need to go on the rollers, OBD1 and exhaust monitor. Harder for the older cars then the newer ones
 

Siciliano15

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1975 model year or older is exempt. You either learn to deal with it or get your car registered out of state. If you car runs good, it will pass. My '94 RT/10 has headers, cat back, K&N and passes every 2 years. Only issue I have is having to keep the RPM's in a 50 RPM band for 15 seconds, the local tech I use knows how to get around the usual monitor grounding (which isn't exacting) and gets the signal from my plug wires directly.

2000 and new cars only use the OBD test, plus gas cap test and visual. So his and my '94 need to go on the rollers, OBD1 and exhaust monitor. Harder for the older cars then the newer ones
that must be tough with the 50 rpms but it sounds like you go to someone who knows what they're doing so thats good. the 1975 deal is pretty crazy thats almost 50 year old vehicles that need to be tested.
 

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