Thread: Power Loss and Bogy Throttle Shortly After Startup/Warmup Every Day - 2001 GP SE 3.1

So it looks like I've come through my slow loss of coolant situation in my 2001 GP SE, after treating the coolant with Blue Devil sealer - everything is working fine in the coolant area, have only added a tiny amount of coolant since the treatment a few weeks ago, a dramatic improvement.

Now I am dealing with an issue that was starting to develop before the leak issue, but has gotten worse in the last couple of weeks - a bogging/lack of power when trying to accelerate, which seems to happen only shortly after the engine has come up to temperature, and then eventually on a given drive, seems to go away,and the engine behaves normally - until the next time the car is driven from a cold start.


The problem is very repeatable, happens like clockwork every day on my drive to and from work. I will start the car, let it idle for a minute or so, and then drive off. In the first few minutes/miles before the engine fully comes up to temperature, it runs normally, and accelerates strongly and smoothly through the gears on local two lane roads that include several long uphill pulls where I am in 2nd to 3rd gear in the 20 to 40 MPH range. About 3 minutes from starting out, as the engine temp gauge comes up and settles around 185, acceleration through the lower gears, even on level ground, starts to feel boggy, like the car can't get out of its own way, its especially noticeable on a long straightaway with a very slight upgrade that I drive on every morning. It's sill slightly boggy as I accelerate up to speed for a run down I-95 for about 15 miles, gradually the boggy acceleration goes away, and by the time I'm off the interstate and back to going up and down through the gears on local roads again, the engine response feels normal.

The same problem repeats itself on the trip home, from a cold start the engine initially feels fine and has normal power. The point at which it gets boggy a few minutes after cold startup after the engine comes up to temperature always occurs just about at the point where I am getting on the I-95 North bridge from New London to Groton, its a long fairly steep uphill pull and the lack of power is really bad there when I am coming onto the bridge at about 30 mph. By the time I crest the bridge I can work the speed up to 65 and can maintain that or more all the way home, and when I am back on the last few miles of the trip over hill and dale on local roads at low speeds, the power and throttle response is normal again. When its at its boggiest, its at its worst when trying to get through 30 to 50 mph range in 2nd and 3rd gears.

I generally am not throwing any codes from this. When the bogginess does occur it often feels like it is rapidly cutting into and out of normal power, but no misfire codes so far. I have tripped a very occasional P0404 EGR valve response code, when this has come in (only 3 times or so) , it happens after I've really tried to goose out some more acceleration with a mashed throttle downshift.

I'm suspecting this might be due to bad plugs and wires (at 94K and I am fairly certain its still on the originals of both). I have had similar types of issues like this on previous vehicles due to really worn plugs or wires, but they usually happened all the time, and did not come on go so regularly during a daily driving cycle. Going to put new plugs and wires in this weekend. I wonder if I am missing something else that might be causing this unusual repetitive problem?

Well, it wasn't the plugs or wires. Just finished up putting in new AC Delco OEM wires and platinum plugs. Had high hopes heading out from the house, things felt pretty peppy while I was still not fully warmed up and apparently was on open loop control. But, right on cue, when the engine warmed up, the boggy response came back, essentially the same as previous. I picked up a diagnostic scanner that reads and records live data and ran some data runs at normal idle, nominal 2000 RPM idle, and during an acceleration run holding the throttle constant along the slightly rising straightaway where I always have the problem. Nothing jumps out of the data as abnormal yet. Seems like the MAF is showing reasonable amounts of intake air flow, the TPS is giving steady and reasonable outputs, the upstream O2 sensor voltage is switching up and down like it supposed to, the downstream 02 senor voltage is hanging around 0.5 volts, generally staying between 0.4 and 0.6, so it doesn't appear to be running too lean or too rich. Going to digest what the data means, and try cleaning the MAF sensor. One thing that seems odd is the ignition timing advance, at idle is showing something like 40 degrees, seems way out of the box. Anyone know what normal idle timing advance should be at idle for the 3.1 V6? BTW, nothing abnormal looking on the pulled plugs, all looked pretty normal, just a light brown color that is usually considered normal in those pictures of what normal and abnormal plugs look like. No erosion/cracking/burnt look, all of their gaps were a jut a little bit wide (.070 vs .070).

Given the recent history of the (now corrected) coolant leakage/loss, for which I never could see a whole lot of externally, and never could smell in the exhaust, I'm starting to suspect an at least partially blocked cat converter. Not as bad as some of the horror stories I've read about online, but on its way. If I cant get anywhere with the MAF sensor cleaning, its going to the shop to have my mechanic check the cat inlet BD outlet temps, and do an exhaust backpressure check. Also, although the scanner indicates that the cat efficiency is OK (and it has never thrown a P0420 code), there are some failure indications for abnormally low 02 sensor switching rate, that apparently do not trip a DTC (yet).

Cleaned the MAF, no improvement, if anything, bogging got worse. Thought I was on to the MAF as a contributor, fuel trim, especially the short term, was tending toward lean most of the time, especially when trying to accelerate. When short bursts of power in the boggyness happened, seemed coincident with the fuel trim finally going positive a bit. Seems to be holding good smooth and steady idle, when holding a very high idle between 2000 and 3000 RPM, vacuum holds steady, does not slowly drop as might be expected with a blocked cat. Upstream O2 sensor showing lots of switching, downstream overall trends toward midrange around 0.5 volts, slowly trends up or down with large throttle changes.

Replaced the MAF, overall some notalbe improvement, but still weak acceleration and power, especially on upgrades. I'm still thinking there is at least a partial blockage in the cat, even though the O2 sensors seem to be behaving properly and manifold vacuum is not slowly dropping on high idle. Shot cat inlet and outlet temps as best i could with a non-contact laser temp scanner, only seeing about 40 degrees higher temp on downstream end (420 degrees) vs inlet (380 degrees) on idle after a long drive. Also, the discharge pressure across the exhaust tip feels notably lower than I remember it to be, and much weaker with my hand held over it than how it feels on our totally normal near new Tacoma's 2.7 liter 4 banger. Is going in the shop Monday for an exhaust backpressure check and cat replacement if indicated. Still don't understand why it runs pretty normal stone cold for a few minutes and then starts to bog after warming up all the time, unless the cat blockage is worsened by high heat. Also, fuel mileage on last fill up was only 17 MPG, way down form the 24 it was getting when running normally.

Got it back from Bob at Kars Automotive in Westerly RI this afternoon.. Clogged cat, as suspected. Bob put in a Walker bolt in factory replacement, also had to replace the downstream O2 sensor because its threads stripped out taking it out of the old cat despite Bob's applying heat and being careful as possible. The sensor tip looked totally normal, as did the upstream O2 sensor, no indication of coolant contamination. Cat probably has been clogging up/breaking down for a while, I can't remember the engine pulling this well in all the time I have been driving it! During the test drive I felt like Mike and Edd on Wheeler Dealers when they finally take their project car out for a run after all the work is done!

In retrospect, some other indications of a clogged cat that were happening toward the end - rich mixture smelling exhaust fumes getting sucked into the car interior from the ventilation system - there was enough back pressure that some exhaust gas was blowing out of the exhaust manifold joints, even though there was no gross audible noise. On a cold start I could actually see exhaust vapor leaking out arond the No. 2 cylinder exhaust flange area. All gone now with the new cat. Also was seeing a notalbe increase in coolant temps after a long uphill pull on the highway. Surprised that the O2 sensor indications and fuel trims with the bad cat were not so far out of whack considering how bad the performance was compared to with the new cat.

Not sure if there is a direct relation to the cat problem, but on Saturday while I was keeping an eye on the fuel trims with the old cat (it was constantly trimming to slightly lean, indicating there was an overrich mixture, but not grossly so, all of a sudden the trim went to insanely rich, well over +10, and then the engine started acting like it was out of fuel, and eventually died. I had my wife bring me 5 gallons of gas, as I suspected it might have actually run out, the fuel gauge has been flakey lately, and with the nominal 17 MPG or less I have getting, it in fact might have gone dry. At any rate, could not get it to restart, and had no fuel pressure , nor could I blleed any fuel at the fuel rail Schrader valve. BTW, the valve is not your standard tire valve size Schrader, its's quite a bit larger. Ended up having the car towed to Bob's with my AAA towing coverage. Fuel pump died, not sure if it went on its own, or it either clogged or overheated due to fuel starvation on a low tank level. Bob put in a new pump and filter, and all is well on that front now as well. And of course I now have workiing fuel gauge since the sending unit is part of the pump.

And to further add to the when it rains it pours story, I had Bob replace a front wheel bearing that just started howling last week- I told Bob I suspected the left one, as I had replaced the right one about 15K miles back. Turned out the original left one was fine, the Timken I put in on the right was gone! Go figure. In retrospect, I did run for quite a while with a bad shimmy in the front end that apparently was due to an out of round front tire, the shimmy went away with a new set of tires a few months ago. Might have put a lot of extra load on the bearing....

Finally, want to put in a plug for my indie mechanic Bob at Kars Automotive in Westerly, RI. Although he is a passionate air and water cooled VW guy, he will work on anything foreign or domestic. Very fair labor rate, and very fair on his parts markup. He's been doing the stuff I can't do myself, or don't want to deal with in the cold winter months for many years now. A very good troubleshooter, he invests in and stays current on his diagnostic tools and software. I highly recommend him if you a looking for a great indie mechanic in the SE CT/South County, RI area.