cjserio

I'm going insane trying to figure out what's wrong with this engine. At around 2,000RPM it pushes me back in my seat as the horsepower builds but less than that, it has very little enthusiasm. I'm not sure i could even chirp the tires if i drop the clutch. In addition, i'm getting about 10-11MPG with a mix between city and highway driving. Lastly, it seems to start up real quick when cold or hot but if it's WARM, it takes 2-3 seconds of cranking to start.

Yesterday, i had it emissions tested and it passed everything except Hydocarbons (HC). Here were the results:

HC = 169 (160 limit)
CO = 1.09% (5.40% limit)
NOx = 32 (7000 limit)

So the truck seems to be running rich I guess? That would confirm what my nose has been telling me. The exhaust has always smelled a bit rich since I got it.

So following the FSM, I tested the O2 sensor by jumping TE1 and E1 and then measuring VF1 to E1. With the truck warmed up, the voltage is a steady .12 to .13 volts. It doesn't fluctuate at all! If i remove the TE1/E1 jumper, the voltage sits at 5V at idle and then once I give it some throttle, it again goes back to .12V and sits there without fluctuation. I even tried pulling the break booster line to create a vacuum leak and the voltage does not move at all though the engine does run very rough.

I sprayed each connection and various spots on the intake with carb cleaner looking for a vacuum leak and found none.

Next I thought it was the Engine Coolant Temp sensor. That would explain the engine being in an open loop which would explain the poor fuel economy, the poor performance, the long start when warm and the failed HC test. I tested the sensor both on and off the vehicle and it's working just fine. I even tested it at the ECU to make sure the harness was good. It all looks fine.

The truck has new NGK plugs, a new distributor cap and rotor, it's timing is dead on at 10* BTDC.

Could it be the O2 sensor? Does anyone know why there is no fluctuation on VF1 like the manual says there should be?

TNRabbit

I'm going to assume 3VZE as you don't state but 10 degrees BTDC gives it away~

How many miles on the current O2 sensor? They REALLY need to be replaced every 80-100k miles, regardless of what spec you get on it. That can make 2-5 mpg difference, depending on how bad it might be.

You are barely over the HC levels so I'm guessing it's not a major thing causing your issue. Possible the O2 is the solution.

Did you check ALL vacuum lines for leaks? passenger side VSVs, vacuum lines to the front diff, etc.? I use Propane or MAPP gas torch (unlit!) to check ALL lines. Also, squeeze your intake hose while you're checking to see if it's got a crack in the accordion section.

You might have a slight leak in your Cold Start Injector....or an issue with the timing switch on it or the temp sensor that's causing your warm start issue.

cjserio

Oops sorry. Yes it's the 3VZE. I'm not sure how many miles are on the sensor since I just got the truck. The wires look pretty clean and new but the flange is rusted beyond recognition so it's certainly not super-new.

Hmm I did not spray the lines to the front differential but I sprayed everything else. I'll have to recheck those vacuum lines.

Like i said, the temp sensor seemed like the smoking gun for the start issue but i'm getting good readings from it even in vehicle at the ECU so it must be something else.

cjserio

Bump - anyone had their O2 sensor ever just output one steady voltage instead of cycling? That's my main question here...Does that point to a bad sensor?

scope103

It COULD be a bad sensor -- one that stays high regardless of the O2 concentration. More likely, it is just telling you the truth -- you're running rich all the time.

But you cannot get that result without a code. So, check for the code, and follow up that. If you don't have a code, I wouldn't have confidence that your check of the O2 Sensor was completed successfully.

cjserio

Sorry I forgot to mention that there is no CEL and when I try to pull the codes i just get the normal flashing light.

cjserio

Well the problem with the emissions/smog was definitely the O2 sensor. I put a new sensor in, the computer began giving me the values it's supposed to and I passed emissions with no trouble.

It still a little shy on power below 2,000RPM but that may be something else...