I recently purchased a used and abused 1994 F-150 2wd Ext Cab 5.0 EFI 4r70w Tran MAF with 160k on it.

I am having problems passing emmision tests with it, (high NO).

I have done searches on this forum and have checked in Haynes manuals, but can't seem to find a definative answer as to the original exaust configuration this vehicle had.

It currently has an after market CAT with a 2 1/2 input/ 2 1/4 output followed by about three feet of straight pipe, ...... then a new Walker muffler and tailpipe I installed.

Walker makes reference to and I have read here about a double or two CAT's.

Did this truck originally come with a double or two CAT's? If so, is there a difference between the two CAT's ?

Thanks

 

Do you still have the emissions sticker under the hood? I believe it is located on the radiator suport. it should tell you what you are supposed to have.

 

Nope trucker, all labels seem to be intack. One under the hood shows emmissions hose routing ect, but no reference to CAT's.

I was hoping that someone that actually owned a new 94 5.0 could remember how it came from the factory originally.

 

factory setup would have been...

two dinky downpipes off the manifolds, about 2 inch's around. drivers side pipe crosses under the tranny to meet the passenger side pipe. Both pipes run side by side into the first cat, the bigger of the two. A single oddly shaped pipe, about 3 inch's around maybe a foot long, exits the first cat and enters the second cat. a single 2.25 inch pipe exits the second cat and runs to the huge canister muffler, and then out the tailpipe.

the only difference between the cats is the size, the second cat is about half the size of the first one. I've seen on other brand trucks there was a cat for each downpipe, on Fords both sides run through both cats. Not sure about F250s or 350s, but on 150s the exhaust was setup the same no matter what engine came in the truck.

 

Hhhmm. High No or nitrides of oxygen, right? NO is caused by high combustion temps. I don't think the cat does anything to NO.

What are your other numbers? Pass on HC? Pass on CO? The cat will help burn off some excess HC, and it's main job is to convert CO to CO2. So, if your numbers on those are OK, then go back to combustion temp. Timing may effect that, along with mixture. Check your specs for timing, and check for vacuum leaks that might lean out the mixture or otherwise effect it.

There are usually some better minds chiming in on this as well, and they may be able to steer you along. Post your other numbers if you have them.

My smog guy says some aftermarket cats are worthless, worse than a worn out stocker. But, yours might be ok if your CO and HC numbers are good.

 

Thanks Jimbo that helps me a lot,....... I might just add a second If my next test fails.

85E150, you answered a couple of questions that I asked in a thread a few days ago but got no response to.

I was getting 334 codes along with a 172.

I found the EGR to be jammed. I forced it loose than cleaned it out with some Blaster type stuff . I also sprayed some silicone into the plunger diaphram chamber and she seems to be working fine now. I also found the vacuum control valve for the EGR to have corroded connections.

I still get the check engine light coming on after about 1/2 mile to a mile after shutting off the engine and restarting. I havn't read the codes since. It might be the 172 code (oxygen sensor) causing that, that's why I am starting to focus on the exaust system now.

My HC was 25 ppm with the limit being 334
My CO was 0 % with the limit being 1.48 %
My NO was 2470.3 ppm with the limit being 1370

I don't know if an EGR could throw the NO off by that much.

Thanks for the responses

 

EGR is intended to reduce combustion temps, so I'd focus on that. Your cat is giving you 0% CO so it's doing something right, and probably isn't the problem.

Only some new made for diesel cats work on NO, so the EGR is, imo, the focus here.

 

Thanks again 85e150

 

Yeah, cats just convert HC and CO into H2O and CO2...nothing to do with NOX. Look into the EGR system first.

 

I have a 94 and opened up second unit on several of my trucks when removed . I can tell you its more of a muffler than any thing . I was told it is a resignator (S.P.) If you go order a oem replacement cat you will get one like the front unit. High NO wouldn't be effected by another cat. Just get a good high proformance cat to replace the one you have.If its the problem.
I checked with local (PA) inspections And they look for the first Cat that it is there not second .

 

Thanks Lost

 

UPDATE ...............................

I went checking to see If I could get the O2 sensor out and discovered that the wires had been cut. I guess the previous owner had changed the Y pipe with a junkyard used one, that contained an O2 sensor with clipped leads. I made some feeble attempts at removing the O2 sensor and failed. The leads from the connector were
long enough to reach the sensor clipped leads with plenty to spare, so I solder/spliced them with heat shrink over the splices.
I then erased the continous memory and took it for a ride. The check engine light has stopped coming on. I read the codes, and I no longer get the 172 running lean check O2 sensor code. I still however get the 334 code "EVR reading higher than expected while EGR is still closed"

This morning I tried cleaning my EGR better, but it seems to be OK, but I get a reading of .83 volts from the EVR with the engine on but not running. I believe I read some place that this reading should be around .5 volts or lower. So I installed an "O" ring between the EVR and EGR, about a .030 gap, which took the reading down to about .43.

Wal..La Erased memory and reread codes. 1-1-1 and 1-1-1

I have about 5 gallons of premium gas in it, gonna throw in a quart of denatured alcohol and get retested in the morning.

 

UPDATE II ...............................

I PASSED !!!,...............but just barely.

I failed to put in the quart of denatured alcohol, but thank God I was using 93 octane.

HC 120.9 limit 134.0
CO 0.57 limit 1.48
NO 1366.7 limit 1370.0

Thanks all that helped

 

my 95 300 had the dual cats, but when i bought replacement system it only had one cat. i guess newer technology since 95 allows you to get the same results with one instead of two.

 

Great glad you passed . You can use 2 can of "Heet" like a gas antifreeze/fuel injector cleaner. 2 can dose wonders for emissions.

Lost in 90's