Truck was running decent for a while until the check engine light came on, it ran rough and rich with hesitation in the throttle. I just replaced my TPS and nothing changed, but I have replaced my other sensors about a year ago, MAF and o2, but it will run great after starting for 3 seconds, but after that it idles down to about 500 rpm and acting like it’s about to die, any thoughts? Spark plugs and wires replaced, same as distributor cap and rotor but timing is a little off, but it never threw a code, throttle body clean

 

Index page of System_Diagnosis-ALL.pdf shown above.
Index page of Diagnostic_Routines-ALL.pdf shown below, if you need just that.

Index page of Pinpoint_Test-ALL.pdf shown below.


If you don't have a scanner like Innova 3145 you can still retrieve the trouble codes by grounding the connector and count how many flash on the CEL, check "Reading and Clearing Diagnostic Trouble Codes" section.

 

How did you determine it was running rich ?

 

I’m sorry for the late response I’ve been reading the pdfs and going back and fourth. I knew it was running rich due to the rich smell and poor mpgs I was getting, and it’s running really rich, 1/8 of a tank to the river and back (roughly 18 miles round trip). But i got the code 98 thru the check engine flash and it told me a hard fault was present. I replaced all my sensors at this point. Someone told me that it could be my fuel pressure regulator? I haven’t read anything in the pdf about it

 

You are strongly urged to buy a Innova 3145 as it's so inexpensive and you will need it to run tests.
If you replaced all sensors and you think they are good you should run Berryman 2611, then followed by a cycle of Berryman 2616. It's much cheaper if you get the 12-pack at than individual cans at your local auto part stores.
Way better than keep throwing random parts at it.

 

Alright, I’ll get ahold of one soon. I greatly appreciate the help

 

You might want to read and learn as much as you can about engine fuel systems and operation because the best tool in the world will only tell you what is happening and you need to know what us supposed to happen along with why and how it is controlled.

Some offer conditions that cause the problem, but you still need to know unless you cover all the possibilities suggested.

 

I’m sorry for being really late but I’ve got my hands on the scanner, I hooked it up and gave me the code 98, a hard fault in the system, but I have replaced all of the sensors, replaced my icm and coil pack, my timing is off but I can’t see how that can throw a code though because it’s ran a bit off for over a year. I have also replaced my fuel pressure regulator. Am I missing something?

 

302 engines without a MAF sensor,code 98 tells us there is a problem with the Thermactor system.
That consists of an air pump a couple of electrically controlled solenoids,and vacuum controlled valves.
There is a Diverter valve and a Bypass valve. If one of the vacuum controlled valves is leaking air, that could contribute to rough running.

Try to do a little reading on the system and it will take the mystery out of troubleshooting the system.

 

I searched around and I found it unplugged and dry rotted, when I tried to reinsert the vacuum line it cracked and snapped. I’m thinking about redoing all the lines and hoses, should I replace the thermactor too while I’m there? I had the scanner hooked up and it won’t read the codes anymore either, I’ll be doing my research in the morning over this and find possible solutions. Cause at the moment it is undriveable, any kind of throttle will make it sputter and slowly rev up while it’s popping and shuttering, it smells rich and won’t keep an idle for more than 8 seconds