2000 S10 2.2 Flex Auto - with a gremlin

[polarsusd81]

I have been struggling with my 2000 2.2 Flex Auto for a while now. Every morning on first start-up for the day when the engine is cold it struggles bad. Idle is fine but if I try to go anywhere it misses and jerks around, rpms jumping all over. Once the truck is warmed up it seems to run better.

In the last six months I have replaced the following:

Auto Trans

Front O2 Sensor

Fuel filter/pressure regulator

Fuel Rail and all injectors

Throttle position sensor

Plugs

Wires

Valve cover gasket (was leaking bad)

Has a code for fuel tank pressure sensor but it has had that code since the day I bought it. The first 18 months with the truck it ran fine with this code, don't think it is the cause. I have the sensor, just don't have anyone that can help me lift the bed to replace it.

I am wondering what else it could be? Maybe something up with the cat and once warm, whatever is clogging it expands and opens up? Coils maybe, but that would probably throw a code and probably not change when warmed up? Someone said maybe a coolant temp sensor but the gauge is working fine? Any suggestions to help me find the gremlin?

At the rate I am going I feel like I should just get something different and garage this truck until I can throw an LS in it. The truck is really nice and clean, full power, fogs, loaded up with everything but a good running engine.

Thanks,

Tom

[Jeremy airjer W]

Have you checked to see what the coolant temp sensor is reading when it's cold?

[polarsusd81]

No I haven't done that yet. I picked up an obdII program ad cable for my laptop, guess I will have to hook it up and see what it says. I also have a spare motor in the garage and can pull that sensor for a quick swap. Is it just standard Teflon tape on the threads to seal it or should I use something different? I will try out the computer obd reader tonight and make sure I get it figured out and then again in the morning when it is cold.

[B-man715]

I had an '01 s-10 with similar issues. My mechanic was stumped with the problem.

After some online research we ended up replacing the flex fuel sensor?? It was behind the passenger side front wheel-well along the frame.

Sorry I don't remember the exact part name, it was several years ago........ You may have already replaced it? I do remember the part was kinda spendy

[polarsusd81]

I sure as heck hope it isn't the fuel composition sensor. Them suckers are about 450-600 bucks. I hooked up the laptop with the obdII reader and everything seemed good, the fuel tank pressure sensor code was there as usual. I will check the temp sensor reading in the morning. Seemed dead on with the gauge this afternoon.

[B-man715]

I see they make a plug in replicator for $150 on E bay. You lose the ability to run E85 but who runs that krap anyway.........

[polarsusd81]

Coolant temp sensor was reading properly this morning when I hooked up the laptop. I took it for a quick run around the block and noticed the throttle position sensor looked to be acting up while it was cold based on the data logging graph. It seemed a little jumpy, would suck if it is the sensor cause I just put that sucker in a couple months ago. Was looking at those replicator plugs for the flex fuel composition sensor, the one site I found gave voltage readings for the different pins on the plug, I will try to check those tonight. Not throwing any codes, even dating back to the day I got it (code history list on my phone) for the fuel composition sensor though.

With all the money I have into it, I would be about 1/2 way to a solid LS V8 setup.

[Jeremy airjer W]

It's not the TPS. The scan tool will not pick up data fast enough to see the true reading of any sensor. TPS sensors will typically give you an intermittent surge at cruise or mess with transmission shifting.

While you had the scan tool hooked up did you look or would you like to share some of the other data you saw. O2 sensor readings, fuel trims, etc.

[polarsusd81]

I can take a look at that stuff again. Fuel trims seemed to be pretty even curves on the data log, intake manifold pressure was high at idle and dropped during acceleration, voltage on the O2s seemed to be pretty consistent, can't remember the exact numbers but the first O2 was quite a bit higher than the second. I will try to see if there is a way to record the info.

[Jeremy airjer W]

The front O2 should be switching back and forth after a couple of minutes of warmup. If it is biased high (over 500mv) than that may be a crucial clue. High O2 voltage indicates a rich condition. If its a false reading it may cause the fuel system to run too lean as it tries to compensate. This would cause a lean misfire. All of this would be a concern in closed loop operation.

The next thing you need to look at is open and closed loop operation. from your description it sounds like the problem goes away after the engine management switched to closed loop. You should be able to see this on the scan tool. If this is the case than there are only a few things the PCM is looking at in open loop. MAF or MAP, TPS, Crank and or CAM signals, Coolant temp. If these are correct than it is possible that we are looking at a "mechanical" issue.

"mechanical" issues could include vacuum leaks, timing, compression, fuel pressure, coils, plugs, wires, etc. My next step would be to monitor engine misfires on the scan tool to see if there is a specific cylinder or cylinders that are affected.

On a cold start a week ignition system may not be able to handle the denser air and fuel mixture. If you have a coil pack that is week (fairly common on the older 2.2 and 2.5 liter engines) you would get a similar symptom to what you are describing. An adjustable gap spark tester would be a great tool to check this. Spark should jump at least 3/4 of an inch form all the plug wires. if one or more is only jumping 1/4 of an inch or less than you found the problem.

[polarsusd81]

Wow, that is a lot to take in but I think I got the jist of it. I have been thinking about replacing the coils for a while now, I am sure they are original to the truck and I am fast approaching the 190,000 mile mark with it.

I will take another look at it Saturday morning with the scanner to see what I can find. I have in the past had a lean bank 1 code on the truck but this was before I replaced the front O2 sensor, haven't had that code come back yet. I will also try to lift the bed up a bit and change out that fuel tank pressure sensor. Just want to get rid of that code once and for all.

Thanks for the help guys.

[polarsusd81]

So Sunday morning I went to Oreilly and grabbed an adjustable gap spark tester and tested the spark on cylinder 4 (1&4) and cylinder 3 (2&3). Spark jumped 1/2" on cylinder 3 and would miss if I stretched it to 9/16", jumped 5/16 on cylinder 4 and wouldn't fire at all at 3/8". I replaced the coils, no change. I think I need a compression test, probably should have done that first. Just ticked off at this point and would rather bring it somewhere than continue to try to diagnose this on my own. This morning on the drive to work it had a serious miss pretty well through out the entire rpm range.

[Jeremy airjer W]

Tested at the coils or at the wires? If at the wires than check at the coils. If spark is considerably better at the coils than the wires are bad.

[polarsusd81]

Wires are new so I would hope they are still good.

[polarsusd81]

It is really odd cause in the afternoon when it is warm, the truck seems to run fine. In the morning with the cooler denser air, the truck barely runs. It seems pretty obvious that something within the temperature monitoring is messed up, but I can't figure out what it is. Might throw a new intake air temp sensor in, but I doubt that does anything. Maybe a MAP sensor (pretty sure that is the one on the top of the throttle body, have two extras laying around).

It cuts out something serious in the colder air.

[Scott K]

Cold means moist, try spraying the plug wires down after it is running good, and see if the problem happens. Your new wires maybe junk.

[Jeremy airjer W]

Sounds legit. New parts are always 100% out of the box , right....

The map sensor should read about 1.6 volts at idle and just under 5 volts at wide open throttle. If those are correct than you can throw maps in it all day and not get anywhere.

I think you need to go back and look at your spark again. You should have the same spark on all four wires which you do not. You swapped the coil with no change. You have not checked spark at the coils to see if you get the same result or if spark is fine. You can also ohm check the wires. They are all roughly the same length and should have the same ohm reading, roughly.

You can continue to throw parts at it or you can test and diagnose, it's up to you.

[polarsusd81]

I should have time to check that tonight. I will check at the coils first, should I just connect the clip to the electrode and hook the wire to it kinda reverse of what you do at the plug end? I will check the wires again too.

[polarsusd81]

Definitely not spark related. All four coils and wires jumped a solid inch with no misses that I could see.

[polarsusd81]

Still to early to say it is 100% fixed, but last night I threw in one of the two spare idle air control valves I had laying in the garage. When I pulled the old one out it had a coating of grime on it. Put in one that had 160k on it and took it for a spin around the block, worked great. The real test was this morning, conditions similar to when it was acting the worst. Fired up and no missing or jerking around the entire drive to work. I am going to give it a week before I call it good, but from the feel of the drive this morning, I think this is going to stick.

[polarsusd81]

It doesn't make complete sense though. The idle air control valve is only supposed to open during idle to allow intake air to bypass the throttle body blade correct? Would a dirty or sticking IAC valve being open during anything but idle cause any kind of vaccuum issues? Just trying to think of how that works so I can learn something from the experience.

It has been running like carp for a long time now in the mornings and only having issues in the afternoon when it has been cooler. But this morning it drove great. Maybe drive it a few more days and see if it comes back, then throw the old valve in just as a test to see if it comes back.

[Jeremy airjer W]

No.

The iac regulates the amount of air that bypasses the throttle body. If the IAC where to stick open the RPMs would be higher, if it where to stick closed it would not idle. If the iac where out of control it would likely set a TPS code especially if it where idling high. Why a TPS code you ask. The computer sees the idle is high and it also sees that the throttle position sensor has not changed. It thinks you are holding the accelerator pedal down since every other sensor seems to confirm this. So you get a TPS low voltage code.

If there was a vacuum leak the rpms would be higher at idle. You can demonstrate this by starting the car, pull the vacuum hose off the power booster and listen for the rpm change. Two things you will notice. The RPMs go higher, and you can definitely hear the vacuum leak. A leak this big would likely trigger lean codes p0171/p0174, any possible a map sensor code.

[polarsusd81]

I had a P0171 code about 3 months back but after doing the O2 sensor it hasn't come back. I did notice a bit of rough idle the other day when I had the computer hooked up. It did also tend to idle high after driving, say when I would park at work or home, idle wouldn't drop below 1500-1600 rpms. Once I shut the truck off and restarted it would go back to normal. Didn't put that together as a clue for some reason. Also had a tps code early this spring, replaced that about three weeks before the transmission swap. I will keep a close eye on it and report back with my findings.

Thanks for the help.

Tom