Well, It looks like my 95 m5od didnt make the idle emissions cut today. I think I have to dig a little deeper into why. Idle and high idle HC emissions for my vehicle are supposed to be under 220ppm according to the great state of NJ. My idle was 816 and high idle was 90. I changed the spark plugs, cap, rotor, wires, air filter, oil and filter and o2 sensor and ran it through again. This time my idle number was 475 and high idle was 90. I am kind of at a loss as to what else can be causing just the idle HC to be higher than the high idle HC number.
All mechanical issues seem to check out ok. Compression is good(160), fuel pressure is good (55), timing looks good at 10 with the spout disconnected. New Isky 256 cam, lifters, pushrods and hi flow cat in 05 and passed the same inspection then so I think I can rule out the cam and cat.
All sensors are giving good info to the computer according to my actron datastream display. I can see what every sensors voltage and output is.
Any help out there?
Thanks.

 

The Cat on a '95 could be worn out/plugged. Three-way high-flow Cats can probably be had for less than $100.00

 

Appears she is running on the rich side. Check EGR and EGR tubes for blockage. Check vacuum lines for cracks and leaks. If you have a MAF, clean its air flow sensors. Make sure all sensor electrical connections are clean as corroded conectors can send bad signals to the ECU (computer). Make sure the throttle body, butterfly valve and intake plenum are clean. Hope this helps.

 

Couple more ideas. Do you have a air injector emmission system that injects fresh air (O2) into the cats? Lack of injected air will increase HC. Check all vacuum lines including brake booster vac line.

 

The cat was replaced in 05 with a hi flow unit on a walker down pipe into a gibson cat back system. It does seem to be rich but only at idle though which is a little confusing. The high idle emissions are way below the 220 ppm limit. I didnt think there was supposed to be any egr flow at idle but Im going to check the vac lines again.
How do you check to see if the fresh air pump is working? I can feel a suction on the intake hose when I throttle up.

 

Since you have sucksion on the air pump inlet it would appear that it is working but I would try to test it at the check valve on the outlet side. So, slow idle is rich but fast is ok. Spray carb cleaner into the throttle body to make sure the butterfly choke plate is not sticking and small air/vacuum holes are not clogged. Not sure of your exact configuration, but double check all adjustments for choke linkage and that may affect return spring tension/position. Are you sure you are seeing all of the sensors on your diagnostic tester? I failed NOx due to a bad knock sensor that did not show a problem/fail on my tester. It took the dealers more sophisticated tester to find reveal an intermittent warning code - that was a real pain in the rear.

 

Please tell us all how you adjust the "choke linkage" on a '95.

 

No egr flow at idle, but if you did have some, it would cause a rich condition. High idle us consistent and good, so closed-loop is running fine. I would test the map sensor and tps, then check for vacuum leaks.

 

The EGR valve introduces exhaust gases into the combustion chamber, this dilutes the air/fuel mixture and leans it out.

How is this going to cause a rich condition? It doesn't.

A stuck-open EGR valve generally manifests itself as an engine running like crap at idle, sometimes so badly that it dies.

First thing to do IMHO is pull codes from the computer, let it help you find the problem.

Fuel Injection Technical Library » How To Run a Self-Test
Ford Ranger/Bronco II EEC-IV Testing

 

Yep, I meant throttle body butterfly valve, not choke. Guess I've been spending too much time with my old 1966 F250. However, a dirty or sticking butterfly throttle valve usually will cause a rough idle but that was not noted. Still I would check adjustment of the throttle arm linkage and position sensor. It appears thread comments have covered all the likely candidates - vacuum leaks, dirty injector, bad sensors or connectors, fuel delivery, ignition, bad catalytic converter or air pump which usually cause both high HC and CO. If not, the computer may be running closed loop but getting erroneous data which it thinks is good.

 

His problem seems to be only at idle speed. At idle, isn't the FI system running open loop? If so, it will not be a problem with O2 sensor or MAF sensor. It could be a bad temp sensor making the computer think the engine is colder than it really is. Once the engine revs, the computer goes closed loop and the O2 sensor tells the computer to lean it out.

If the system runs open loop at idle (and I don't know for certain if it does) then look for a temp sensor problem or some other non-EFI problems mentioned above, like low air flow from the air pump into the exhaust/cat.

One more thought just came to me: Are you still using a 195 degree thermostat? If you have changed to a cooler thermostat, it might cause the EFI to run rich at idle.

 

Good point about open vs closed loop. If you are going to work on your computer controlled auto/truck at this level of detail you really need to get a Fleet Service Manual or equivalent. An FSM provides detailed descriptions of all the truck's systems including emissions systems, diagnostic proceedures as well as the logic used by the computer to control engine operation. Just a thought, but the forum should set up a library of FSMs or equivalent manuals for all of the trucks discussed. It would support forum discussions and might help the original poster answer thier own question if we had a library of manuals we could all go to for reference.

 

Great thought, and I wish we could do it.

Clear the copyright stuff with FoMoCo's lawyers and maybe something will happen. Maybe... we're all volunteers here, and this sounds like a lot of work....

 

No maf on a 95.

Egr displaces oxygen. If egr is introduced when not expected, you get less oxygen and a richer mix. No egr when expected gives a leaner mix.

Your eec4 computer is open-loop enriched idle and uses map, tps and iat sensors.

Check your smog pump solenoud valves and make sure they are sending air to the cat at idle.

The Haynes manual for these trucks has one of the best map and tps sensor checking procedures I have seen.

If there a teeny leak at the map sensor, it will only show at high vacuum (idle), and be swamped by the open throttle plate at all other conditions. The abnormally high map reading at idle would cause a rich condition.

 

M5OD is manual trans, so whatever engine it will be MAP sensor bank fired. One of the things another group I'm on (my sig may give a hint) found a fresh oil change will help idle emissions. The system should be in closed loop at idle with a warm engine. EGR should not open till part throttle.

Did you by any chance change to a lower temperature thermostat? You said you installed a new cat in 05, how about the O2 sensor? Recommendation is bite the bullet and get a Motorcraft one. Check your PCV system, it pulls a bit of air through at idle, that's why a fresh oil change helps. Good luck with it, I'm glad I don't have those here, my 86 would probably give them a fit.