Did some diagnostics on my 1988 F150 300/M5OD today after horribly failing NOx emissions yesterday.

<u><b>Item 1. Fuel MPG</b></u>
~270 miles on the front tank (~20gal) mixed stop-go/higway= 14mpg (AWFUL, but maybe I'm expecting too much)

<u><b>Item 2. Pull codes</b></u>
<UL>
<li>General Codes:
67- Neutral switch

<li>Continuous Memory Codes:
33- EGR Not Open/ Not Responding (EVP EVR PFE)
41- Running Lean (Fuel Control)
87- Fuel pump circuit fault (check inertia switch) / intermitten in primary circuit.
</UL>
<b>Item 3. Partial EGR vacuum test</b>
Disconnected the EGR vacuum line and hooked a vacuum gauge to the line wihle revving the engine. No vacuum. Zero.

The truck runs well; and has plenty of power. Never feels like it's starved for fuel, and the MPG proves it.

Codes 41 and 87 are probably due to a fuel filter somewhere.

What about Code 33?
<ul>
<li>I'm going to test the EGR valve itself tomorrow. Apply vacuum to it at idle, see if the engine chokes.
<li>EGR controller module?
<li>What about a larger vacuum problem?
<ul>
<li>Sometimes the engine doesn't behave real nice just off idle when cold, it bogs out a little bit.
<li>When I start the engine in the morning, the brake pedal drops an inch as vacuum builds.
</ul>
</ul>

Any advice/help/hints?

Thanks.

 

Update: Haynes manual said the EVR was defective; I disassembled the EVR to see if I could rebuild/refurb it. Turns out the Haynes manual is incorrect. The EVR couldn't physically do what the Haynes manual said it was supposed to. So, I concluded the EVR was good, Haynes made an oversight on the late model EFI emission systems, and went to the EGR. I'd tested the EVP earlier, and that was good. Turns out the EGR body had a dent in it where it mates to the EVP. Straightened the dent with pliers, plus some high-temp silicone, and it passed a quick vacuum test. Now it's reinstalled to cure overnight. Reconnect the vacuum and power when I get to the gas station, and it should pass.

I temporarily have the vacuum line to the EVR plugged; the truck runs soo much smoother without the constant vacuum leak.

The EVR can be disassembled by:
1. Remove the top cap.
2. Pull the prongs out with pliers (no real damage)
3. Unscrew the center pole (5mm socket worked)
4. Work the top metal piece out with pliers. Work it around at each end, and eventually it will come.
5. Tap the body upside-down against your hand, and the guts will fall out. Solenoid coil, steel disc, spring.

Will post the retest results tomorrow.

 

Failed again. Does the cat or pre-cat on an '88 handle NOx as well as HC and CO? Cat could be original.

 

Blue,

I'm with you on the Haynes manual. They can't cover 16 years in any detail, and always seem to omit mine!

I'm trying to ID a clattering noise & have looked at all sorts of forums. Don't know whether this applies to you, but apparently the in-tank fuel pumps are rather problematic - if one is failing, it affects them both (www.2carpros.com). Is your rear tank getting less mileage, or otherwise misbehaving?

I can probably scan the diagnostic procedure for your DTC #33 if you need it.

 

NOx is directly related to EGR function. The EGR should not open unless your above idle and below WOT, with vacuum applied to the valve. The valve requires exhaust back pressure and vacuum to open. If you pump away with you vacuum pump and hold the throttle a tad above idle, you should get an erratic idle each time you pump. It is not uncommon for the valve to fail opening when it should if it has years and miles of carbon built up inside it.