Can codes be present W/O engine light ON?

[99MERC]

Hi,I'm new to the forum and love this sight! I have a 99 MERC.Mount V8 and the other day it just wouldn't start.It was about 28*F out and I thought my fuel lines frozze.So I put it in the garage and heated it up with a turbo heater and still no luck .It acted like it wanted to fire ,like not enough fuel or something is what it acted like. so out of frustration I just held the gas pedal to the floor and it fired up rough and then cleaned up and still fires up no probs.No lights for the check engine or anything showed! Now my reliable Mountaineer is now labled NOT RELIABLE till I can find out what caused this? Can there be codes present that won't trigger a check engine light that can make problems? Is there a way to check W/O a OBDII tester? I'd Hate to drive it and get stranded with my 18 month old Daughter onboard! ANY IDEAS WELCOME! FYI, The truck is maintained very well and has 108,000 miles on it.Never has gave a problem since new! I paid $28,000+ for this BN 1999 NEW left over in 2000! It can't give out, I almost got it paid for!!

 

[Turdle]

You have a very sound and reliable vehicle. Don't worry
The most likely culprit( been seeing a lot lately) is the fuel pump relay, located in the power distribution panel under the hood.( owners manual will showw location, look up fuses in index)
Secondly, you might have had some condensation occur, especially if that was the first cool spell after a warm day( really reaching though)
It might be a fuel pump going out, but usually( not always) they just quit for good

I would get a new fuel filter and fuel pump relay, put them in yourself, and sleep good tonite

 

[99MERC]

Can the relay be intermiten like that or stick? I thought relays just go out kinda like a fuel pump...one second there,then gone kinda thing.I Had a fuel filter put in less than 5000 miles ago on routine matinence...Thanks for the advice!

Any thoughts about it being a TPS? I had one act up on a buddies blazer ,but it idled up and down then wouldn't stay running...

 

[Turdle]

Can the relay be intermiten like that or stick? I thought relays just go out kinda like a fuel pump...one second there,then gone kinda thing.I Had a fuel filter put in less than 5000 miles ago on routine matinence...Thanks for the advice!

Any thoughts about it being a TPS? I had one act up on a buddies blazer ,but it idled up and down then wouldn't stay running...

Yes the relay can , and will go out intermittently, the contacts seem to go bad
You mentioned a 18 month child. I recommended the replacement because I wouldn't want to waste priceless time troubleshooting a 15 dollar part

 

[dogfriend]

To answer your question in the title of the thread:

Yes, it is possible to have pending codes set without a Check Engine light. Some of the self tests require that the "problem" be present on more than one drive cycle before the Check Engine light is turned on.

 

[dogfriend]

Also, regarding your starting problem:

Because the engine started when you held the pedal to the floor, it is possible that the engine was flooded. Normally you shouldn't touch the pedal when starting the engine, but if you hold the pedal to the floor (WOT) you signal the PCM that you have a flooded engine and it will cut the fuel injector time on to help clear the flooding.

 

[99MERC]

Thanks for more replies, I drove it around town yesterday and it almost has a light stumble as it comes down to a idle in gear and recovers itself to a pur. No misses on the plugs, I idled it up very slowly to about 4000rpm and smooth as butter. Then I gave the 5.0 hell :fire: to see if I could starve the fuel pump and make it stumble and it held its own strong!!Plus I always got about 15-16 mpg out of it on HWY.Latley it went to 17-19 kinda weird???and now this little mishap...

I never touch the throttle pedal when starting the truck ,I know its fuel injected and so on. I know the probability of the truck being flooded at the time was less than 1 percent. I just smashed it down out of OLD SCHOOL take that if ya will on the sixth ingnition try! I didn't even expect it to fire up though....

 

[Runnin'OnEmpty]

Merc, I'd try cleaning the IAC (Idle Air Control). They tend to give trouble like you described in the last post. Carbon builds up in the IAC pintle, and reduces the idle quality. Do a search and you'll get lots of info on cleaning them. Basically two screws to remove, spray with brake cleaner, maybe dig out carbon with toothpick or small pick. Then give the mechanism a squirt of WD-40.

Nice ride.

ROE

 

[99MERC]

Thanks ROE, I'll look into the IAC. With 108,000+ miles I don't know if thats ever been replaced , checked or even cleaned for that matter (under normal servicing).I know I never did it but the trucks been in the service dept for various diagnostic checks before.Like I said, I'll check the IAC out plus I was thinking of the O2 sensors(replacing) but I'm sure they would throw a check engine light though....? With my weird MPG gain?? Funny thing is I used to get 15 mpg HWY now its 17+,I pulled my 12' trailer with two MX bikes and a quad over 2000lbs and get 14-16 mpg now!Before it was 10-12 mpg!

I may go to a local autozone or something and have them hook the OBDII up and see if any thing comes up...with their handheld.