What OBDII wont show?

[JackLikesTrucks]

What kinds of things can cause an engine to stall while driving that won't show on an OBDII?

My truck is a 2002 2.3L and stalls while trucking on down the road.

New fuel everything.

No CEL (yes the bulb's good). No codes.

What would shut down an engine yet NOT throw a code?

 

[john112deere]

I don't believe the OBD2 system can sense fuel pressure.

I know I lost the fuel pump in a 2000 Focus and it never threw a light, or any codes.

 

[Jason]

It could be anything. OBDII doesn't store codes instantly. If something just plain went, with no warning, leaving the engine disabled OBDII wouldn't know it.

 

[adsm08]

You are both right to a point. Not every system can sense fuel pressure, but not of them, including his truck can.

OBDII won't set a code off right away. It SHOULD show in the pending codes.

I'd start with a fuel filter and then test the coil.

 

[JackLikesTrucks]

Thanks so far. Rreading this made me think of the OBDII codes in the book show 3 codes for 3 levels of fuel rail pressure problems. But then it does not mean the Ranger has the sensors for it....

It has new filter, pump, and relay without any difference.

Only thing iI've noticed...when she goes dead, I pull over and if the fuel pump doesnt whirrr on restart, she doesn't start. After several tries, she'll whirr and restart.

So maybe bad fuel management part of the computer? Someone said its integrated into the firewall computer.

 

[zukirider21]

you're definitely on to something with the whirring of the pump. my 89 was that way. if you didnt clearly hear the pump make noise for a few seconds before startup, it was a no-start for sure. but if you brought the key back to off, and then back to on, let the fuel pump do its thing for a few seconds, it would fire up instantly.

maybe the fuel pump controlling system is on its way out...

 

[pimtool]

OBDII is mainly for emissions, if its its a problem that doesnt cause excess pollution no codes.

 

[snake]

I know you said you replaced the relay- but this problem sure sounds like a bad one. Try wiggling the wires underneath the relay box next time it does it and see what happens. We've had a few posters on here in the past that found faulty connections at the FP relay where the connectors were crimped to the wires. look for any corrosion, or a "wide" connector that needs to be crimped tighter, ect.

 

[Jason]

OBDII is mainly for emissions, if its its a problem that doesnt cause excess pollution no codes.

Wrong. A lean condition won't cause excessive pollution but will surely set a code.

 

[JackLikesTrucks]

Well, free tests first.

AutoBone fuel pressure tester to the Schrader valve, drive around, and see if there is pressure at the time of stall. No pressure = bad fuel system, Pressure = bad something else. At least I can rule out fuel for free. Otherwise, I'm pulling a used pcm for $75.

 

[adsm08]

Wrong. A lean condition won't cause excessive pollution but will surely set a code.

+1 on the wrong.
-1 on the lean causing no extra pollution.

OBDII watchs for anything that could cause excess pollution, indicate a situation that may cause it soon, or a situation that could cause damaged to the vehicle by continuing normal operation. It also serves as a diagnostic aid for things like RKE, door ajar switches, anything electrical or electronic. Those can be run and tested with the OBDII system.

A lean condition can cause extra pollution. Contrary to what you might thing a lean running engine runs hotter. The primary toxic pollutant from the engine is NOx, and its only produced at engine temps above 2500*F. The leaner an engine is, the hotter it is, the more NOx it makes.

That is one of the functions of EGR, to cool the cylinder to keep it below 2500 and reduce the NOx output. The Cat is supposed to clean up the rest, but if you are blowing out too much it can't get it and react it all before it blows out the back.

 

[mentalbreakdown00]

have you replaced the main ecm relay, it powers the fuel pump relay

 

[pimtool]

Wrong. A lean condition won't cause excessive pollution but will surely set a code.

A lean condition leads to misfire, misfire leads to catalyst damage, no cat leads to polution.

 

[Jason]

A lean condition leads to misfire, misfire leads to catalyst damage, no cat leads to polution.

A slightly lean condition will not necessarily lead to misfire. For example, a small vacuum leak will not cause the engine to run poorly, change mileage or even change combustion temps enough to matter, but will still trigger a code.

 

[pimtool]

A slightly lean condition will not necessarily lead to misfire. For example, a small vacuum leak will not cause the engine to run poorly, change mileage or even change combustion temps enough to matter, but will still trigger a code.

Dont really wanna argue, but it wont trip a code until the fuel trim numbers or air flow numbers or some other pre set caculations are out of range. Which means you may not be able to tell the engine is running poorly bt the computer has specs and if the numbers are not within specs you get CEL.