Issues with V6 SOHC engine running rich

[Justin_]

Hey guys I've been having some engine issues the last little bit here. As I mentioned in a previous post I had a bunch of misfire codes on my 98 sport with the V6 SOHC. I replaced the plugs, wires, and coils, and eventually replaced the fuel injectors once I found that the issue was a bad injector on cylinder 6. I also went ahead and at about the same time replaced the timing chain tensioners. At first I used some eBay one, but they were terrible and made rattling noises. After that I got some ones from the local dealership. When I went to put the new ones in I had a hard time getting the driver side one out with a wrench, so I pulled the sensors out of the thermostat housing, and eventually pulled out the housing and used a socket to switch it over. After I did that the ECT gauge no longer functioned and I got a overheat code once (even though it was fine). The gauge on the dash just sits dead center and does not work. Around this time I also replaced the fuel pump assembly

After all this I started having the engine run VERY rich. It would stall if it idled too long, and would almost stall if I hit the gas too hard coming out of a light. I tried poking at a few things and checking connectors, but I eventually took it to a mechanic that is reputable in town. The mechanic took 6 hours and charged me for 3 to tell me that there was a kink in the fuel return line and its actually running a bit lean now. Not a cheap bill for a kinked line, but if it works, it works.

Coming out of the mechanics shop it felt good, but after a day of driving it was throwing rich codes again, a bit sluggish coming out of stops, and not accelerating as well as it should. Nowhere near as bad, but not right. Talked to the shop and they said the next thing to do would be to replace the cats and O2 sensors. Not sure how cats would help, and I replaced the O2 sensors not 10k miles ago so I thought I would take another look at it.

Doing some research around the internet I found that when an engine starts up the fuel mixture is based on the ECT sensor, and not the O2/MAF sensors and that a bad ECT sensor can cause an issue with the handover leading to rich codes and less than perfect performance. With the ECT gauge acting up and the occasional overheat code when its running fine im thinking that /could/ be related and is what I am looking into now, but I would love to get some other ideas if anybody can think of anything better.

Thanks!

 

[donalds]

Your thermostat housing should have 2 coolant sensors
Brown one. Is dash gauge and a gray one for the computer

If yours only has one sensor
Its for both

I think you have the two sensor model
Replace the gray one its for the computer only

I'd replace the whole housing with a metal one

 

[Justin_]

There is 2 sensors. Bringing this up on an OBD II reader shows that the PCM is getting the correct temp. I had a bent and thus loose coolant cap. /Maybe/ that had something to do with the overheat code I got once. Still not sure where that came from. Anyway, new cap and new dash side thermometer and i'm good there.

Looking at the MAF with the reader the readings seemed a bit off. I have another 98 SOHC, so I swapped the intake hose with the MAF and 1 other sensor (might be the IAT sensor?) and the problems got a bit worse. Sluggish at lights, and not quite as powerful around 70-90 MPH as I have come to expect. So I tried pulling the cable off the MAF and the throttle response became TERRIBLE, but it had closer to the power I expected and felt better on acceleration out of lights and such. So I switched the tube and sensors back and got a new MAF (had been wondering about it before anyway and had already tried cleaning it once) and the truck feels great. Throttle response is back to normal, acceleration is good and power at 70-90 MPH is about what I would expect.

I would say that we were at about 94%/95% performance with the old MAF and now we are at about 98%+. I'll need to see what the mileage is like. I've never seen it much above 12 city, but I had always blamed that on the 4.10 gears and the 31" tires.

I did 60 or so miles on the highway and didn't get any codes at all, so highway is good. Driving 10 miles around town I did start getting bank 2 rich code and bank 1 is probably not far behind. I am still interested in that, but now that I am back to the power I expected im happy. I have an 1100 mile road trip coming up later this week so i've been a little more vigilant than I normally am with these things.


Mechanic said that between the injector issues I was having previously and the engine running rich for a while and super rich for a bit the O2 sensors might be bad and leading to the code. Anybody think there might be anything behind that? It was running rich enugh to cover the recently replaced tail pipe in a lot of sut, so maybe they are dirty even though I only replaced them 10K ish miles ago.

 

[Justin_]

Thinking of it I replaced the upstream sensors, but I don't think I ever replaced the downstream one. I might start there and see where I get.

 

[C420sailor]

Downstream just monitors cat efficiency.

What do your fuel trims look like?

What injector issues did you have previously?

 

[Justin_]

Downstream just monitors cat efficiency.

What do your fuel trims look like?

What injector issues did you have previously?

Good to know

I don't have a reader that can read that out. I am planning on borrowing one to take a look soon

Injector 6 was intermittent, then shortly after failed. Couldn't get new ones from Motorcraft so I got some "ULTRA-POWER FJ307" ones from RockAuto

 

[Justin_]

Coming out of my trip here, i've got another 1500+ miles on the truck in the last few weeks. I actually had an engine lean code while running down the highway. Still running a bit rich on the streets, but not bad. The revving is almost gone, no new carbon on the tailpipe, and just feels all round great. Going to reset the PCM codes here shortly and see how long it takes to get the codes again. It seems like after the kinked fuel line the MAF was the biggest problem even after cleaning it.

Still looking to chase that last 2-3% back to stock performance. I like keeping this thing running well. Hope to have it for quite a while.

Wish I knew what the miles were. It came with a switch to disable the speedo and odometer. All I know is it has at least 90K miles. lol.

 

[Justin_]

Ok, so it runs well once warmed up, but before the engine gets up to temperature that is when it struggles. Revving and burning rich.

Normally as soon as I start it up I am on the gas and off to work, but I idled a bit today at startup and it was struggling.

So its something that matters more at startup than running. Has a new MAF and IAT sensors and the coolant temp sensor seems to work fine looking at the OBD readout.