Bad coolant sensor = rich condition???

[Ken Cunningham]

My car has run rich since the day I bought it 2 years ago. My BLMs in normal driving drop right down to 106. When I change to a chip that expands the bottom to 95, then that's where I run.

The latest issue of the BGNRA newsletter has a little blurb about the coolant sensor, saying that the ECM uses input from this sensor to adjust fueling. If the car is cold it can tolerate more fuel. If my sensor was reading low, is it possible that would cause a rich condition across the BLM table??

 

[salvageV6]

Quite possibly.

It is easy to ohm the sensor out in various temps. to see if it's working right.

Chart for the ohms per degree F is in the service manual. Well it could be in degrees C.

 

[Eric Stage I]

What are the other readings from your scan tool at idle, warmed up? Maybe we can spot something there.

Regards,
Eric

 

[Ken Cunningham]

Temp at idle is 168-170 on the scan tool, just like the reading on my vdo gauge. My BLM at idle is forced by the Thrasher to 128, my O2 is 750ish (on my scan tool, key-on, engine-off O2 is 495, so my reading is a little higher than DS or TL). I noticed my IAC was at 0 in P, then I shifted to R and saw 11. I set my TPS for a fairly low IAC count. My MAF is an after-mkt rebuilt showing 5 in P, and 6 in gear. Other readings (1st # in P, 2nd # in gear): Load 33, 46; TPS .43, .43; rpm 900, 750.

Anything in those numbers??

 

[Eric Stage I]

The scan tool is showing you the temp that the ecm is seeing, so that shouldn't be a problem. Your other numbers don't indicate an obvious problem. You might try a non-thrasher chip to get the maf reading at idle, because the thrasher alters that number at idle. It should be 5 or 6. Even then, the maf sensor could still be off.
Are the injectors real bluetops or 868's? The 868's can run richer down low if you use a bluetop chip.
Is the fuel pressure reg. working properly (reducing pressure under vac)?
You could have a leaky injector. You'll need a fuel pressure gauge to see how fast the pressure leaks down after shutdown.

That's all I can think of off the top of my head.

Eric

 

[750H.P.V6]

Ken,

The coolant temp. displayed on the scan tool is what the computer sees and it sounds like it's believable. You stated your O2 voltage key ON enging OFF is 495 mv. Is this with an OTC 4000E scan tool? if so then it's fine. What fuel pressure are you running to get the open loop O2 votage where you want it?

Neal

 

[Ken Cunningham]

Thanks for the replies.
Eric - I didn't know that the Thrasher altered the MAF readings at idle...a slightly mis-calibrated MAF may be the culprit. The injectors are tru-Blu Ford blue tops. The AFPR seems to work fine; I have a fuel pressure gauge that I can mount on the hood. I don't keep it there full-time, but I have kept it there for a couple of weeks and saw nothing out of whack, except I do have a very rapid leak down of pressure at shut off. I will drop 10# in just a few minutes, all pressure within about 2 hours. I don't think that its the injectors, tho. I don't have a hard start, flooded engine problem. No black smoke at start up.
Neil - I use an AutoXRay XP240 scan tool. "What fuel pressure are you running to get the open loop O2 voltage where you want it?" This is an interesting question. I have set the static f/p to 42#, as per the Thrasher instructions. I have never heard of setting f/p to get the open loop O2 where I want it. I don't even know where I want it. Since the Thrasher sets a rich idle to gets its signature smooth idle, I don't know that 750s are out of line for an idle count.