[AB91'coupe]

i took the car to the emissions last night and it failed instead of having .80 or below of hydrocarbons it had 1.75 the guy there said the fuel wasn't burning right. i need help any ideas just let me know.

 

[AB91'coupe]

i have a 4.9 cadillac coupe deville sorry for not being clear.

 

[kingphil69]

id check the EGR valve first, but that's just me. ive got an 88 4.5

 

[DFBonnett]

Any codes present? What is the maintenance history vis a vis tune up, etc?

 

[jamesmdx1]

High HC could be oil that needs changing if everything else it good (no codes) inc. the cat. converter
If EGR was bad it will increase the NOx emissions
try changing the oil and use a good fuel inj. cleaner and try premium gas before the next test
this worked for me, hope this helps

also take it to someone you know.. there are alot of scam artists out there that I feel deliberatly fail cars to offer services for you to purchase in order to make you car pass. I had experienced this a few times here in NY with PEP BOYS, where my vehicle failed and took it somewhere else and it passed
just my 2c

 

[adalla]

Use fuel injector cleaners ONLY with full tank of gas and try to empty it asap (long trips etc.) Fuel injector cleaners are hard on fuel pump's winding's insulation. Despite cleaning EGR passages (two tubes inside throttle body under the plates) never hurts, EGR is mostly responsible for NOx as it was mentioned.

 

[91TexasSeville]

Here are the most likely causes for your 1991 to fail emissions testing. Not necessarily in correct order

1) Leaking fuel pressure regulator (easy check, moderate replacement)
2) Bad oxygen sensors (should set a code, front easy, rear not so easy)
3) Catalytic converter (sounds like a marble in a coffee can upon cold startup, but goes away when engine warms up...muffler shop repair if you don't have the tools)
4) Dirty/Clogged EGR (very easy fix)
5) Leaking fuel injectors (moderate check, easy fix once you check)
6) Dirty internals, engine oil -and/or- wrong grade fuel. (easy fix)

I don't know what your local laws are but in my area, you are allowed only ten days from failure to retest (assuming an expired inspection sticker).

 

[KHE]

When you had the car tested, was it fully warmed up? Make sure you drive it for 10 miles or so to get it fully warmed up.

 

[ewill3rd]

Does the car run okay?
What kind of mileage are we talking about?
What kind of emissions test is it? I mean is it a two speed idle test or are they running it on a dyno? Does it fail for HC under load or at idle or both?

To clarify a few points, a catlyst can fail without rattling... the catalyst bed can become contaminated and just stop working. I have seen many broken cats that were still working. It's not uncommon for both things to be present, I just wanted to mention that they are not necessarily tied together.

EGR valves can cause high HC at idle if they are sticking open but the primary purpose of EGR is to reduce NOX. Did it pass for NOX?

Things like misfires, leaking injectors, bad O2 sensors or ISC problems could cause HC failures but I'd need to know more about the type of test you have in order to give you more info.

Changing the oil is a good idea but if the engine is running okay it shouldn't be much of a factor. Misfiring engines will get high HCs in the crankcase due to the quantity of unburned fuel getting into the oil.
You could have internal mechanical problems also, or bad ignition timing, worn plugs, bad wires... the list goes on and on.

A reputable shop should be able to do some sort of diagnosis to identify your problem. Taking a copy of the failed test should help them if they know what they are doing. Heck you could have a thermostat stuck open or a bad coolant temp sensor.

HTH

 

[Bill$torey94Deville]

i have a 94 sedan deville what you might need to do is run a bottle of fuel injector cleaner, test for spark cuz i had my plug wires replaced at 75k along with spark plugs as suggested in the owners manual but i always burned hightest in it. when i pulled out the plugs they looked like they just came out of the package! im not kiddin the plugs looked like new. Check your O2 sensor and the catalytic converter. if that still isnt helping any check your egr valve. i cleaned mine around 110k. also does your car have any strange noises? knocks pings? if so put a better higher octane rated fuel run it for a couple weeks on the higher rated octane (i burn 93+ and on some occasions i burn 110 racing gas) the engines are aluminum and i believe the heads are too so look for something that you can add to the fuel to help reduce carbon build up. but start off simple- fuel injector cleaner, higher octane rated gas, check air filter too, and so on.

 

[Bill$torey94Deville]

My car also has the 32 valve northstar 4.9

 

[adalla]

My car also has the 32 valve northstar 4.9

Northstar is 4.6 not 4.9

 

[ewill3rd]

The Northstar has a 4.6 liter displacement. The 4.9 is an older OHV motor with a single camshaft.
It's kind of confusing I know, just wanted to clarify.
All it takes is flipping that second number upside down