This all started this summer on the way back home I was going to pass someone and when I stepped on the throttle it would jerk back in forth for a bit then all of a sudden shoot up in rpm like it should backfire jump around a little and then go back down in rpm, I continued to try and make it home like that the problem became worse until finally I made it about a mile from my house and it died while I was trying to crawl it home at that point it was barely running. I let it sit for 30 minutes came back started right up then I thought I had the problem the TFI module, so I ordered a new one and replaced it(the original one was still in it after all those years) but after replacing it I found out that the new TFI didn’t change anything. I tried to drive around a bit for a couple days to maybe get an idea of what’s going on same thing I would start it up just fine and let it warm up and if I tried giving it a lot of throttle it would backfire and jerk around, at that point I had given up for a bit and now I pulled codes on the thing and only got EGR codes and O2 codes, so I said hey why not replace all the sensors in the vehicle as they are all original I replaced MAP, EGR, EGR valve on the left passenger side fender, EGR pressure feedback sensor, O2 sensor, Intake charge temp sensor, coolant temp sensor, idle air control sensor, throttle position sensor. Before replacing all the sensors I decided to try and take it out to fill it up with some gas on. This is the first time I’ve fired it up in winter the thing started like normal but when I went to town it ran like a lot better in the cold it could just be a fluke. After replacing all the sensors I still have the dreaded O2 lean code and EGR stuck open or closed, I took the fusible link out of the O2 sensor wire and it got rid of the O2 code for a little bit I took it for a spin with all new sensors and the O2 sensor hot wired and it still does the same thing I’m at a loss right now hopefully someone can help, I’ve also checked all vacuum lines

 

Assuming you have a Bronco II since that is the section you posted this in, what year and what engine? Have you checked the timing and fuel pressure? “Why not” go ahead and replace the old sensors? Because now you have, unfortunately, introduced multiple variables by replacing all those sensors. Are the new parts better than the old ones? Maybe. Maybe not since the quality of new parts is so hot and miss.

 

1987 2.9l EFI I have not checked timing but fuel pressure seems to be fine it sprays pretty high, my main concern or what I think is the real culprit is the o2 sensor I had a code 41(system lean) and even after replacing the sensor I still have the code I checked the ground to the sensor and it has a good ground, the code is always on even when the engine is cold doesn’t matter if it’s warm either it’s still there, runs really rich too and you can smell gas in the cab occasionally

 

“Sprays pretty high” isn’t accurate enough since 15 pounds of pressure would spray pretty high but not be enough for the engine to run. Lean codes with a gas smell isn’t right. Have you checked under the truck for a leak from a hose or the tank?

When I get home I will try to look up the pressure in my service manual.

EDIT: fuel pressure should be 35-45 psi

 

no there are not any leaks in the fuel system, i would have to check the fuel pressure at a shop as I do not have a gauge, it acts like it gets too much fuel and drives pretty well until I floor it then it just bucks and backfires, but if I slowly apply the gas I can get up to speed. I just find it really strange that the o2 code won’t go away I also occasionally get a knock sensor code saying it wasn’t sensed during the test

 

During the engine running test, when prompted, you need to mash the gas pedal to the floor and immediately release it. You might also need to step on the brake pedal and turn the steering wheel.

It sounds like you are doing the KOER test but you don’t do that test until you repair all active and stored faults from the KOEO (engine off) test. So you have repaired everything there and have moved into the engine running test?

 

yes I have fixed everything that shows up, and have done multiple KOEO and KOER tests but 2 always remain the code 41 and 33 both will not go away and I will occasionally get a knock sensor not sensed

 

Stored codes that won’t clear?

 

I think they clear it’s just that they keep showing up because something’s still wrong

 

Lean codes but running rich is odd. Bad injector(s)? The engine running fuel pressure tests with and without the vacuum hose connected plus a pressure leak down test will hopefully tell you what’s going on. You could also test the coolant temperature sensor for resistance. It could be that the computer thinks it is very cold even when the engine is warmed up.

 

Ive replaced the coolant sensor already and that didn’t change a thing, but I will have to get a fuel pressure gauge so I can test the fuel system, I have not replaced the fuel pressure regulator I have the part I just haven’t gotten the fuel line disconnectors

 

You replaced the coolant sensor, with the two wire connector, because it failed the resistance vs ambient temperature test? Don’t replace the regulator “just because”. Is the diaphragm leaking fuel into the intake manifold?

 

yes I have replaced the correct coolant sensor and no it had no signs of failure before replacing it, I have only checked the diaphragm for fuel leaking back once but I can check again

 

Although you have been given some really good advice, at this point if it is coughing up through the intake, I would check the timing chain as it may have stretched just enough to put the cam/crank timing out of time. If it's not coughing up the intake, then I would look at ignition. Also a tiny vacuum leak can be created as a result of thermal expansion... so getting the engine hot and doing a smoke test migh be the answer as well.