Hello, This is probably an uncommon question but my truck will absolutely not throw any codes or have the check engine light come on. First problem, tip cracked on #4 injector and it threw a code telling me miss fire on #4 cylinder, that was 2 years ago. Now this year i have had 3 coils go bad causing the truck to barley run under a load and the check engine light never come on nor did it give us any codes on the scanner. Fuel pump went out causing the truck to not go over 3000 rpm under any circumstance and hesitating its way up to 3k, it also did not throw any codes. About 3 month ago the #2 rod bearing went causing a horrible knock so i have just completed a full overhaul of my 5.4l engine now has about 2k on it and it seems that at about 2500 to 3500 there is sort of a dead spot or it seems like it just kind of is gutless. other times it is perfectly fine and especially when its cold it runs great. i don't think it has anything to do with my rebuild as i have great compression and the truck has plenty of power most of the time. im thinking its fuel related again but id really like to know if anyone has any idea why my truck will never give me any codes. Here is some info that might help on why my truck doesn't throw codes or why there would be a "dead spot" when warm

2000 f250 5.4l 2v
-295,000 miles did a full rebuild
-250,000 miles replaced instrument cluster because the old one burnt up due to a bad alternator(check engine light came on and threw codes since then but not anymore)
-replaced cam sensor, crank sensor, knock sensor and every other internal engine part besides cams and crank
-8 brand new coils
-new fuel pump 2000 miles ago
-obviously new plugs since rebuild
-motor is all stock beside being bored .20 over and having a "high" flow cat and a flowmaster super 10

I'm sorry for the long post, just wanting to make sure i gave you all the information i could.

Thanks for any help.

 

It's probably not supposed to. Read this thread in its entirety:

https://www.ford-trucks.com/forums/1...bd1-obdll.html

 

You seem to have the same misconception as many others, that the check engine light is supposed to come on whenever the engine malfunctions. That is simply NOT TRUE. The purpose of OBD I and OBD II is to monitor the EMISSIONS. When a malfunction occurs that causes the vehicle to exceed the EMISSIONS standards, the check engine light comes on. A lot of malfunctions can occur that DO NOT cause the check engine light to come on. The OBD codes in the computer can often help when there is a problem, but remember that OBD codes are ONLY EMISSIONS related. As the years have gone by, all manufacturers have improved the diagnostics data in the computer to include a lot of other very useful information for other malfunctions, but the check engine light is there to warn that the vehicle is outside of EMISSIONS standards. The other "vehicle manufacturer specific" codes are for diagnosing other problems and may or may not cause the check engine light to come on. Most of the lower priced scanners only read OBD codes, not the more advanced diagnostic codes.

 

I have no misconceptions regarding WHEN the MIL is supposed to come on.

That is incorrect. While MOST DTCs are emissions-related, not all are.

The OP asked WHY his MIL isn't coming on for misfires. The thread to which I pointed him explains it in detail.

 

ProjectSHO89

First my response was intended for the OP, not in response to your statements. Sorry that I did not make that clear. Second, I have read many of your posts and have great respect for your input. Third, if you re-read what I posted, I did not say that all DTCs are emission related. I said that all OBD codes are emissions related. That is totally correct. I clearly stated that other DTCs that are manufacturer specific are in addition to OBD codes. Sorry for any misunderstanding, but I stand by what I posted.

 

Thanks for the responses, and yes i definitely had the wrong idea about my check engine light. I always thought it was meant to telll me when anything was wrong misfires, emissions, or anything. but thanks alot for the responses

 

I would also note that many malfunctions do not immediately cause the MIL (check engine) light to come on. On many vehicles, the misfire count must reach about 20% before it triggers the MIL. Some EVAP problems must be on for several engine cycles before the MIL comes on. These "temporary" malfunctions are stored in the computer as "pending" codes until the count reaches the predetermined amount and triggers the MIL. This prevents a lot of "false/nuisance" MIL problems. The emissions testers are not concerned about issues your car might have, but only about if it meets emission standards. Did you ever hear " if the check engine light is on, it is an automatic failure"? Wonder why? Also worth mentioning is the blinking vs steady on MIL. On most vehicles, the blinking light means that the malfunction (such as a severe misfire) is serious enough to damage the catalytic converter(s) and the vehicle should not be driven except in a real emergency. Have you checked the price of catalytic converters lately?

 

Does the lamp light when your starting with the
rest of them during the lamp prove-out?
Could be a bad lamp if not.



Sean

 

I ran across this today on the motorist.org site. It seems to support my original comments.