I have a 1988 E250 with a freshly rebuilt 5.8 engine in it. It has less than 1,000 miles on it but it was due for its smog test. The van runs strong and smooth, pulls like a big block and never had any problems, until I took it in for its smog test today. The technician came out after running the test and told me the van failed "miserably" and that the check engine light is inoperative. The smog readings were as follows: HC (PPM) 302 at 15mph and 303 at 25mph, CO was 5.12% at 15mph and 5.19% at 25mph (max. allowable is .56% and .59%) the NO was 321ppm at 15mph and 314ppm at 25mph with a maximum allowable of 694ppm and 596ppm. So, now I have a registered Gross Poluter. Problem that I have now is that the check engine light was operative right up until they ran the smog test as I had checked if for any trouble codes before I took it in this morning. Also, it never showed any sign of a rich mixture until they ran it on the dyno on their smog testing equipment. I was in the waiting room and saw the black smoke and went out to see what was going on. As I was paying my $80 bill, the technician told me it was probably the fuel pressure regulator as all Fords have this problem. I informed him that it was a new one as were the injectors and I didn't think that was the problem. When I got the van back home, I hooked up my scanner and it will not communicate with the van. Something is amiss here. So, I am open for suggestions. Anybody have any ideas that might be of help here?

 

You could try replacing the o2 sensors if they are old, they could be faulty, as for the code reader refusing to communicate, try disconnecting the battery for a few seconds. Perhaps they plugged a code reader up with the ignition on and caused a shock to it.

 

I did replace the O2 sensor but the problem turned out to be a blown fuse (fuse #18) that controls warning lights on the dash, making the check engine light inoperative, along with a broken plastic vacuum hose inside the black plastic covering that goes from the intake plenum to the EGR valve. I took it back to the smog station yesterday and it passed with flying colors. The CO went from 5.12 & 5.19 to .44 & .42. What a relief!! Thanks for the input though.

 

I have an '88 with the 5.8 as well. Engine was rebuilt 36K miles ago and runs well. I did replace the cat and O2 sensors later on. It failed a test once but the tech said that I may not have warmed up the cat enough. When I went for a retest I drove the van for about 20 miles including some highway miles. It passed with flying colors!

 

You may want to look into replacing all of the plastic vacuum lines in the future, they get brittle and crack with age.

 

Well, here I am, 2 years later but with the same problem, same van. This time the readings were worse! Vehicle has only 4,226 miles on it now with the completely rebuilt 351W. It runs strong, like always, smooth, no misfires or anything. But here are the readings from today: HC @ 15mph 178, @ 25mph 124. CO @ 15mph .43, @ 25mph .21. NO (PPM) @ 15mph 891, @ 25mph 942. So, I am totally puzzled and devastated. Don't even know where to start but am sure open to suggestions! Anyone??
Thanks in advance.

 

I just found out that there is a trouble code flashing, 54. Don't have a clue what it means though. Any help?
Thanks

 

54 - Intake Air Temperature/Air Charge Temperature Circuit Open Since the engine is speed density, it will not know how much fuel to inject or air to take in unless its running in closed loop mode.

 

Thanks for the reply. At least now we can look that up in the service manual and maybe find a circuit or part that is defective. The van runs great, just won't pass smog again here in California. I was thinking it might be something with the EGR valve.

 

In speed density, the IAT sensor is very important. Check to make sure its plugged in, then visually inspect the harness back to the ECU. If the IAT sensor isnt sending data, the engine will run rich or lean, and shoot HC and NOX out into lala land.

 

Hi! Thanks for all you input on my problem. Do you happen to know where that switch might be located on my 1988 E250 with 5.8 engine? I have the intake air sytem and filter off and cannot see anything that resembles what an IAT or CAT switch is supposed to look like in the air filter assembly or the intake manifold area. I appreciate your time with this, it's beginning to make me lose some sleep now as I need to resolve this before my van is registered as a "Polluter" here on the sunny west coast.

 

Its on the intake manifold. Its threaded and screws in. It kinda looks like a knock sensor or coolant sensor.

 

Got it!! Many thanks, I am off to the parts house to get a new replacement. This one is actually black and oily, might just be the problem!! I will let you know. Thanks again, you may haved saved my sanity!

 

Double check the wiring and harnesses to make sure nothing is melting/rubbing/broken as well. Its not always the sensor itself that is bad.

 

Hi!
I did check the wiring and harnesses and connectors for conductivity and all was well. Major noticeable was that the smog pump stopped pumping air into the air cleaner after I installed the new switch. I just came from the smog station and it failed again. Slightly better readings but way above the maximum allowable. The HC was 178 and is now 175, The NO was 891 and is now 753. CO and CO2 were relatively unchanged at 14.1% and 0%. Smog guy says its time for a new catalytic converter in his humble opinion. So, looks grim to me. Many thanks for your help. I'll let you know how it goes.