Hey guys, thanks for all the input. My latest update is I noticed the idle does seem to be a little lower than it always was before. It is dropping to around 700 rpm which doesnt seem right. It was always right at 800- 850 rpm.
I checked all my vac lines and replaced a few and put clamps on the nipples just to be sure. The airb and aird solenoid plastic vac lines were replaced because they became hard and brittle.
I checked the secondary air injection system and it is working correctly- air bypassed at startup briefly and then gated to the head for a short while and then diverted to the cat for the duration of the run cycle.
The thermostat is the stock unit and the o2 sensor is a new bosch installed just before the inspection.
The egr system checks ok with and without the restrictor mod. I will definately look closer at the tps and map.
Ive pulled codes several times and all seems fine by the pcm. Code 111 system pass. This and the fact I can actually see what each sensor is sending to the pcm keeps me from wanting to shotgun all the sensors. The actron unit shows the entire data stream for every sensor with a reading for voltage applied to each and its output to the pcm. Coolant temp, Inlet air temp, map, iac position, tps position, starting fuel trim, ignition advance, system voltage, canister purge and a few others. Actron Elite autoscanner 9185. I picked this one because of its capability of interfacinig with OBD1 vehicles with the data stream instead of just reading and clearing codes.
Luckily, I have a bone stock 94 4.9 m5od to compare with. This one has a perfect idle and runs circles around my 95. Everything I have done to my 95 has not increased or even made it comparable to my stock 94. I checked the secondary air system, fuel pressure, ignition timing and advance,vacuum and compression on that and verified my 95 was ok. Even before I did the isky 256 and exhaust system, the 95 was still a totally different running setup than the 94. The 94 pulls instantly when you let off the clutch without giving it any throttle wheras my 95 had to have some throttle or it would stall. I figured surely a freeflowing exhaust and the 256 cam would have done something but it wasnt much. The 94 still has a rock solid 800 rpm idle and pulls excellent.
I even put in new injectors with the cam and exhaust mission. Didnt change a thing. Mechanically both years are identical. The head is the same for 94 and 95 as is the block, crank, rods,and pistons.
The datastream from the 94 looks damn close to the 95.
It may sound weird but I might have to try swapping the pcm from the 94 into the 95 to see what it will do. I compared both pcm pinouts and they are identical and they both have the same trans and rear ratios. The 95 never ran as smooth as the 94 from the beginning of this journey. I think I need to pull the pcm anyway just to see if there could be leaking dead capacitors on the pcm board causing this kaos.

 

FWIW, I have had bad luck with Bosch O2 sensors lately, I think they are not being built in either Germany or North America.

 

Atta' boy !!!!!

You've done a great job checking all the sensors and readings from them and determined the problem must lie within the computer (pcm).

What most folks don't seem to understand is how important it is to have a pcm that interpets correct input data, and outputs the correct data to the electronic components that allow our engines to run correctly ie. engine management.

A leaking and/or dead capacitor(s) in a circuit board will wreak havoc on how a piece of electronics will work (pcm input or output)......our nearly 20 year old pcms have endured thousands of hot and cold cycles and if I remember correctly, electrolitic capacitors do have a life expectancy.

Let us know what you find.

Bob

 

[quote=Truckin Bob;11608714]Atta' boy !!!!!


A leaking and/or dead capacitor(s) in a circuit board will wreak havoc on how a piece of electronics will work (pcm input or output)......our nearly 20 year old pcms have endured thousands of hot and cold cycles and if I remember correctly, electrolitic capacitors do have a life expectancy.

Not trying to hijack, but I just wanted to share that my son's 1984 4.9L [feedback system] original computer is still working and passes emmission testing! [28 years young] Amazing!

 

If you're close to passing already you might try running the tank low and watering down the gas with a few bottles of HEET fuel line deicer. It's methanol, and alcohol burns a lot cleaner than gasoline.

 

Gonna try the pcm swap this weekend if its not rainy. I thought about the Heet in the gas tank and probably will if It gets to that. I just wanted to try and fix the problem instead of masking it. There is also some stuff called "guaranteed to pass" to add to the fuel I saw at Advance. I might have to if all else fails and I get hammered for driving around too long on a rejected inspection sticker.

 

- then there's always the "register with a friend outside the idiot-area" method...?
Ohio has those useless laws in four or five of the major cities. I know a number of people who have simply "moved" for the day to another area and registered their vehicles there. And if anyone ever asks - then you've just "moved" to where you are for real not-too-long ago..

 

I've heard that a few ounces of acetone in the gas will help with passing emissions tests.

 

Excellent idea on the electrolytics. I don't trust them that old in my living room stereo, so I definately wouldn't trust them after 20 years of vehicle duty!

Even if the capacitance checks out on a meter, the ESR may have risen so much it no longer functions in circuit. Best bet is to shotgun replace them all.

 

Well, the saga continues. I went through the emissions inspection and failed again. This time I replaced the PCM, tps, throttle body gasket, pcv filter and ran a bottle of Guaranteed to Pass. My idle HC is down to 275 so I am getting closer to the required 220.
I think it is time to replace the cam and lifters with the stock unit and check my bearings while im in there. The Isky 256 cam passed inspection last time so I am a little confused and trying to get back to square one with this problem.
Since it is only low idle HC that are high, I am wondering if it could be a bum injector. Fuel pressure is fine.
I really dont trust any of the private inspection garages around here to work on my truck so I am going to keep digging....

 

Well, fourth time is a charm i guess. It finally passed the emissions test. I dont know what the actual reading was but it had to be below the 220 limit. This last time around I replaced the injectors and coolant temp sensor and ran two bottles of HEET to a quarter tank of gas. I figure it could have been the injectors because when I ran some cleaner through, it dropped the HC number even more but not enough to pass. I put the HEET in the gas as added insurance.
Thanks for all the input and I hope this helps someone else having issues with high HC emissions at idle.