My 2000 did. I'm guessing he meant the CEL light won't come on for one?

 

I talked to a friend of mine who is going to check it for me when I am not so busy at work. I was wondering the same thing about the CEL and the codes. Will it still read on the computer when he checks it even though it's not throwing a code? I drove it yesterday and really paid attention to the shifting and the shimmy. I am pretty positive it is not the tranny now just by the way it comes and goes in relation to the RPMs. I also can notice a slight miss at idle along with the tell tale smell of rich exhaust fumes.

 

You say it's not throwing codes. Just trying to understand, have you plugged in a scan tool and checked? Or just guessing because the light isn't on?

A misfire code will not set the CEL unless your truck is rated for California emissions.

 

Haven't scanned it yet, just set it up with my buddy who owns the scanner when I am off work next. I am currently working 6 days a week on midnights while the union is on strike at my plant. I drive my work car back and forth, it gets a lot better mpgs than the V10 would. He also has coil packs also, so if we do find the culprit we can correct it right away and plan on changing the rest out later.

 

Really? I wonder why it only applies to CA?
Learn something new everyday.
Tom
Is there some logic here to understand? Interested in why it wouldn't apply to all states, especially if it helps diagnose the issues?
Thanks.

 

California trucks have different ECM's.

 

As I understand it has to do with the requirements of OBD-I vs OBD-II. I read a document a couple years ago that detailed the differences between PCMs. In a nutshell, a misfire code on an OBD-II certified car or truck must set the CEL. The logic is that this is an emissions-related failure that should cause the car or truck to fail inspection for those states that don't use a sniffer for emissions.

Since this won't fail an OBD-I vehicle the light doesn't have to be on when this code exists. I started searching about this after I had one active and two pending misfire codes on my old Excursion but no CEL. Non-California trucks of this vintage may have the OBD-II plug, but they are OBD-I certified.

 

Many of the manufacturer DTCs will not cause the CEL to come on. The MIL or check engine light is NOT an engine diagnostic monitor. It IS an emissions monitor. Its purpose is to let you know when the engine emissions are outside of the parameters set for your vehicle. The emissions DTCs are sometimes helpful in locating the problem but do not necessarily pinpoint the cause of the failure. Other manufacturer specific DTCs are put there to be seen by a scanner tool to assist in locating various problems with the engine, transmission, ABS, etc. but they do not generally cause the CEL to come on unless the problem effects emissions. The CEL would have been more appropriately named the Emissions Malfunction Light.

A scanner capable of reading ALL of the DTCs, not just OBD DTCs, is usually the best first step in diagnosing any poor running engine. These scanners use the same port connecter to read the codes as the OBD-II scanners, but provide much more information and capability.

OBD-II scanners are made/used to assist in locating emissions related problems.

 

I have a 2000, F250, Crew Cab, V10, 4x4...... and had bad coils intermittently failing causing your exact issue. Low RPMS and high RPMS it was fine but it had a sweet spot that was bad. This will also not cause the check engine or any fault codes to be logged. Very annoying.

 

Great conversation here.
I would then ask, if it's a emissions monitor, why wouldn't a misfire, causing an emissions issue, not activate the CEL in vehicles 96 and newer using OBDll technology in any state?

On another note, when taking my wife's 2004, all wd Volvo in for testing, I wondered how the test shop would measure emissions when it can only spin two tires at a time?
I found out that newer vehicles, here in CA, don't emissions test with exhaust pipe monitors anymore.
The OBDll monitors so accurately, that if the CEL isn't on and it's passed its internal testing since clearing any codes, the state relies with the "on board" computer to communicate any emissions issues or lack thereof.

 

Vehicles over 8500 lb GVW were exempt from the full ODII requirements for a number of years.

Example My 2001 will not report a bad Catalyst and does not have a Oxygen sensor down stream of the CAT to check for a bad CAT. It only has the upstream sensors.

I think The socialist state of California required both sensors in 2001.

State inspection in Texas use the ODII codes for emission requiring tail pipe inspection for ODI vintage autos. Therefore I can get a inspection with a bad or empty CAT.

 

Update: Went to friends shop and scanned motor and #7 misfire came up. Replaced coil pack and she's like a new truck. shimmy went away and a considerable power jump. I wanted to thank everyone who gave info for my problem and look forward to chatting again.


Matt

 

That's great to hear Matt, thanks for posting up your solution!

 

That's Good news. Hope you have good luck like I had. I still love mine. Over 230,000 miles now.

One blown plug and a fuel pump. Still going strong.

 

That's what I am hoping for. Need it to last until the kids are a little older. May be able to invest in a new one after that. thanks again.