Hi All, I posted a couple days ago with no responce. i really don't want to bring my truck into a mechanic or worse yet...the DEALER. This is my first Ford.

Truck is running really rich in idle, i can see gas vapour coming out the tailpipe and black smoke. really lumpy and does shut off occasionally. It started hesitating while i was driving on the highway at cruising speed and then started happening when sitting in idle.
I have changed the rotor,cap, wires, plugs (i'm changing the plugs again tonight to another brand), air filter, fuel filter. cleaned the IAC last night with no difference.
I am going to check for error codes tonight but i did leave the battery disconnected for a couple days.

questions:
-since the battery was disconected, do i need to drive around for a while then check for codes?
-what would be the next thing to change or check?
-can i adjust the timing on this thing?
-common causes of engine running rich with hesitation?

Any help is much appreciated.
thanks
1991 Ford F-150 5.0 (302)

 

one possibility is the Fuel Pressure Regulator.

I don't know exactly where it is, but there is a vacuum line attached to it. Pull the line off. If there is gas in it, you need a new one. If it's dry, on to the next possible culprit.

 

changed the plugs this morning, gapped correctly. checked fuel pressure regulator and it is dry. cleaned the IAC again and started her up. still hesitating on idle. i took her out for a drive to get the sensors warmed up so i can check the error codes. i noticed something. during acceleration there is no hesitation or bucking. hesitation only occures during deceleration, crusing, and definetly during idle. i counted the flashing engine light and i will decode the numbers later today. i am going to pick up an error code reader today and run the test again tonight to confirm numbers...but..are these symptms pointing to the IAC valve? comments?

 

Yeah, sounds like a timing issue. You should be abe to adjust the timing. You'd need a timing gun. Have you ever adjusted timing on other vehicles? If so, I won't go into the details. Haynes manual, or the like, would be good investment.

Also, timing could be off because your timing belt is stretched/worn. Might have to get a shop to replace. Normally not a thing for your average backyard mechanic.

Good luck,

Joey

 

Timing belt? On a 302?

 

Sorry, don't know much about those. Is it a chain, then? That's what my Toyota has. And they do wear/stretch, file teeth, etc.... Can necessitate the need to adjust timing.

Educate me, please.

 

Should be a gear with a chain on the 302, unless Ford made something I am not awate of.

 

not a belt. it is a chain. i will double check the timing tonight.

 

Does that engine have a CAM position sensor? I had one go bad on my 93 SHO and it ran exactly like that. But that would certainly set the MIL light and a code.

 

can't find anything on a CAM Position Sensor. Would that also be the Knock Sensor??

 

it sounds like an idle air controll valve to me. They can be "cleaned" but its not a perminant fix and it rarely works. some have perlonged replacing by spraying carb cleaner or something in it. what do u mean by hesitating? if it is the iac it will drop down to really low rpms and jump back really high to try to correct itself. this occurs mainly during idle but also during deceleration and will drop occasionally while maintaining a constant speed. however it will not happen during acceleration. Is this what is happening?

 

your bang on the money BuiltFordThough. that is exactly what happens. to bad i ordered the MAP, O2, coolant sensor, and anything else that effects the idle. i will report what i find after i change the IAC.
Thanks

 

Dang, sorry I missed this. Shoulda put 302 in the title. IAC should take care of ya.

Adrianspeeder

 

Well Gents, here are my results. This is a bit long but this is far more entertaining than a soap opera. https://www.f150online.com/forums/im...lies/smoke.gif

step 1: Replaced the IAC valve last night and crossed my fingers. started her up....same thing. lumpy idle and running rich.
step 2: might as well replace the coolant temp sensor because I bought it....and no change.
step 3: reset the computer and take her for a drive. I figured maybe the CPU needs to re-learn all the new components I changed. Took her for a drive... exactly like before I changed EVERYTHING,..hesitation during cruising and deceleration, idle surge when stopped. So I drove back home to check the KOEO and Continuous Codes.

let's re-cap::So far I changed the following in this order and checked idle operation after each change (just adding this to help people with future debugging):
Air Filter / PCV filter / Fuel Filter / Rotor/Cap / Plugs / Plug wire / MAP / PCV valve / IAC valve / coolant temp sensor

KOEO codes that came up after the drive (BTW-these codes were not displayed before I changed the above components)
121-Closed Throttle Voltage higher or lower than expected
Contin Code
122-Throttle Position sensor circuit below minimum voltage

Well that's interesting. The Haynes manual states that a malfunction of the TPS (throttle position sensor) will cause idle surge as the fuel will try to compensate for false air flow intake based on throttle position. Thanked my wife for counting engine codes with me and went to have a look at the TPS wiring. The wire on the very left (looked liked the ground wire) was exposed for an inch or so. no insulation on it. This has caused corrosion on the copper strands which will obviously increase resistance in the wire. increased resistance causes less electrical current flow which in turn leads to lower voltage. I moved the wires around on the connector and tried to push them further into the connector. started her up...ran perfect. occasional lump but overall ran great. took her for a drive. ran great. came back home and checked the error codes. KOEO reported 111-system pass. that confirmed the wiring or something on the TPS was in fact at fault.

went out this morning and started her up again, started running like crap. the air was fairly humid so I was not too concerned. the condensation can effect the exposed wire.
I am going to re-do the wiring harness going into the TPS as I feel this is the core issue...actually, it better f@#$ing be the issue or else I'm taking a flame thrower to the truck.
Question: is this a harness that simply comes off the TPS or do I need to remove the throttle body to get to it on the underside. anybody run into this issue before??

Thanks again guys. you have been a huge help. hopefully this thread helps others in the future.

 

I am not as familiar with the 91 302 as the 88 302 but on EEC IV equiped vehicels you cannot change the timing without removing the "Spud" connector. Where is the timing now? Last time I adjusted timing I think it was idling around 22 with a max of 38; "spud" in. It drops when the "spud" is out and that is the base timing. The spud in 88 was right near the distributor , a gray plug on a section of 2 wires, one in one out. Looks similar to a fuse or fuse link. The computer actually handles timing curve, didn't notice any cams or weights in the distributor did you. Adjusting the timing while "spud" is pluged in only increases the gap between rotor and cap!!! What did the plugs look like??? Do you know how to read them?? Do a search to find. How about the TFI module on the side of distributor or firewall, although that usually causes ignition only related issues. How many miles on truck? Is it running on all 8, plugs will tell you. Or pull an indivdual ignition wire at a time, no RPM drop dead cylinder. Do you want more bad news. I belive EEC IV also has a computer limp home mode > allowing you to get home with a bad computer. A bunch of non variable paramenters to fall back to. Not sure when Ford switched to EEC V. Need more specific info.

Good Luck Sarkis
David