92 4.0 Ranger high HC at idle (failed smog)

Hey all, I have a 92 4x4 Ford Ranger 4.0 that this year is having issues passing smog. I replaced plugs (oem autolite), wires(duralast crap), idle air valve(also duralast crap), cleaned MAF and throttle body, PCV valve isnt stuck and rattles fine, recently replaced the intake manifold gasket as coolant was leaking out of one corner as well as the plenum gasket, sprayed around for vac leaks with no noticeable jump in rpm, and I am still having trouble passing smog.

I do have a Solus Pro that I got a few months ago and am very new to so I don't quite understand the data I am seeing. I saved a movie file at idle (warmed up) and at 2,500 rpm but I don't know what or where to ask for help to figure out what area I need to look at. I am failing HC at idle, the rest of the tests are a pass, there is just to much unburned fuel. Truck idles a little rough but not like a miss. I ran different fuel system cleaners as well as the "guarantee to pass" stuff but no luck. My truck has always passed smog with flying colors but this year something is not letting it pass. Smog guy said the cat is operating fine, as I thought maybe the cat could be bad. Fuel pressure I checked and was in spec. No codes were present before this smog test or are now. I just replaced the plug and wires because the first time I went to smog the truck the guy did a pretest and the HC numbers were way high even at 2500 rpm so he didn't even run it and suggested plugs and wires which I did and changed things significantly. I bought it back and he pretested it and it looked like it would pass which it did on every other test but not on the idle. Max was 120 and I am 135. I am still to high. Smog guy said check for vac leaks which I have done already with no idle change. Here are my smog results
Idle-773RPM %C02= 14.7.....%02=0.4.....HCPPM= 135 and MAX is 120..... C0%= 0.05 and MAX is 1.00

2383-RPM %C02=15.1.....%02=0.1.....HCPPM= 40 and MAX is 180...... C0%=0.14 and MAX is 1.00

I wish there was a code thrown so I could narrow it down, but such is my luck. My plan of attach is to get help understanding the data I saved and find out if anything jumps out as being out of spec and start testing. I have a Fluke 98 that is an oscilloscope and multi-meter in one, that can test just about anything on an electrical system but I need to know what to start looking at.

When I replaced the intake manifold gasket I checked the injectors and checked the spray pattern and they all looked fine. I believe I replaced the small brass filters inside and put new o rings on. I have other used injectors to try if need be. This truck has high mileage as most 92 trucks do, like I mentioned smog has never been an issue. I never did anything to "prepare" it in the past, just took it in and it always passed.

Truck has a flowmaster muffler, and K&N filter other then those 2 things and a small suspension/body lift its all stock. Runs fine, starts fine, power is normal, I drive it every day so its not like there are other issues I might not be seeing.

I tried to give as much info as possible, but sure I forgot something. Any and all suggestions are welcome. If someone has the shop stream program that understands the numbers/graphs I would really appreciate it if I could email it and hopefully find out if anything is out of wack. If there is someone that I can email it to, shoot me a message at diebog1 atgeemaledotcom

Thanks all for your help

Jeremy

From your description... sounds to me like you have an injector or two that just aren't sealing up causing a rich condition at idle. Would also explain the less then smooth idle you are describing.

What's the best way to go about finding a lazy injector? I have olm checked them and when I had them out I checked the spray pattern which was a nice fan spray. Unplugging each Injector won't really show which one it is, so is there a way to check and find which one? Or does most just buy all new Injectors and hope for the best?

Also forgot to mention the old plugs were on the white side but they were pretty old. I would think a vac leak but with an unstable idle it's hard to see if there is a difference. Some say use propane some say water, some carb cleaner, what's the best way to find a vac leak?

Also anyone have a link to a PDF for the service manual for a 92 Ranger with a 4.0? I always find them for my other cars (f250, nisssan frontier, ford escape) but I cant find one that isnt corrupted. Thanks

I'm really going back a long way in memory to remember my emission testing days. If I remember correctly a rich mixture will elevate HC levels and CO levels will be closer to normal. A lean condition (lean misfire) will raise both HC and CO levels.

Having said that.... a cylinder balance test would be the way to determine a cylinder that is causing the problem. A piece of test equipment would electrically disable each cylinder one at a time... then note the rpm loss during each of the individual cylinder tests. The cylinder with the least amount of rpm drop would most likely be the culprit.

If you don't have test equipment to perform that test (most DIY'ers don't) a handheld infrared temp gun is the next best thing. Point the gun at the exhaust manifold ports where they connect to the head. Look for a temperature difference across the individual cylinders. Find the one with the highest temperature differential and you again have found the culprit. Remember that cooler temperature would indicate a rich condition... hotter temperatures would be lean condition.

I have a snap on Solus pro but there isn't any option to do a cylinder balance test for this year/model. When I was diagnosing a missfire on my wife's 07 Nissan frontier I was able to do a cylinder balance test and shut off each cylinder. I guess I can do it the manual way and pull a wire. I hate getting shocked though it's not fun.

I have a fluke ir gun so I'll try that method. I never thought of doing that. Thanks for the suggestion!

@diebog

Do you know what pages you might need? I haven't started the digital conversion yet but I just recently acquired the service manual, electrical, vacuum, etc manuals from eBay.

Let me know and I should be able to do some scanning.

Just a thought. After many attempts to get my son's B2 to pass, (failed HC at idle) I checked the cat and discovered it was gutted. A new one brought the HC at idle from 200 to 6. The HC at idle was the only parameter that failed.

Any ideas to finding lazy injectors? This year truck doesn't have cylinder contribution tests available.

2trux said:

Just a thought. After many attempts to get my son's B2 to pass, (failed HC at idle) I checked the cat and discovered it was gutted. A new one brought the HC at idle from 200 to 6. The HC at idle was the only parameter that failed.

Click to expand...

Thanks for the sugg, the smog guy said the cats are working great, I don't know how he can tell though. Mine has 2 cats it looks like back to back, ive read about cleaning cats with dawn and a bucket of water or using lacquer thinner in the tank. I might look into one of these

No luck using the temp gun?

You may not see huge differences.

I tried but there were so many differences depending on where I aimed it. Its hard to reach one side so it was inconclusive. I have a nice Fluke gun so I am sure its not the gun being the issue. When you have done this test in the past what area are you measuring? For example if I checked the outer side of the exhaust manifold I start at one end and end where the header connects, the temp would get hotter and hotter the closer to the header I got. My guess is the combined heat from each cylinder made the metal hotter. So when checking the furthest one there was only one cylinder putting heat into it. As i move along to the second, now there is 2 cylinders adding heat. At least that's my theory.

My next test I tried to get as close as possible to where the engine and manifold met and I was getting more consistent temps but as I mentioned the passenger side with the AC box above the manifold its hard to get to. Driver side was super easy. But the numbers jump around when holding still on one port. How much difference would I be looking for? 5°F, 10°f? More? Also should this be checked at idle or 2,500 rpm?