Ok guys, I"ve been at this for a week and gotten nowhere. So I"m looking for some ideas.

The Problem: After its been running for a minute or two the car will not idle and will not accelerate at anything but WOT. It will buck and kick and sounds like its running on one cylinder. Its fine if I just start it and drive away cold and will run perfect for a minute...then it deteriorates until the car wont move.

Some background:

I tore the car apart to replace a blown torque tube a few weeks back.
Drove it for a week then thought I noticed a little hesitation at 10% throttle on a couple of occasions. Seemed to go away.

A week ago I removed my supercharger and flashed my car back to a stock 98 tune(have EFIlive). Had some idle issues but ran ok for the first day. It does have a small cam in it (221 .575 112), but I drove the car around with that cam on the stock tune for 9 months previously. I figure it just needs to learn out the idle. The next day I felt some hesitation at low RPM low throttle situations.

Two days ago I tore the torque tube out again to replace the pilot bearing with a bushing(to hell with needle bearings!).

The problem has gotten progressively worse.

For a while I was convinced it was a tuning issue and tried tuning it out. Got nowhere. Even flashing back to the stock tune the problem is still 10x worse than it was a week ago. I'm no professional tuner..just followed some tips on more spark below 1200rpm and playing with Throttle Cracker and such.

I tried replacing the MAP sensor.

I've check for vacuum leaks and even capped off everything that isnt necessary just to eliminate things.

I thought it was temperature related(ei the car switching to different tables for air/fuel/spark)and it seemed to happen once the temp got over 170f or so. So I removed my thermostat and set my fan temps to make the car run cooler(160). Still there. So its not directly linked to coolant temp.


What drives me nuts is the fact that the car starts and runs perfect for about a minute, then just craps out. Anyone have any ideas ?


P.S. Funny enough I had decided to trade the car in and thats when the issues started

I"ll edit in eliminated possibilities so everyone doesnt have to read the whole thread to see if a suggestion has been made yet.

-I did change back to N/A spark plugs.
-Only threw a code once (MAP sensor) low idle. I replaced the sensor but I think the code was an effect, not the cause.

 

Just a long shot, but do you still have old plugs in the car? The gap between those from a FI to N/A is huge. Are you getting a engine light?

 

What codes do you have in memory? Pull your "P" codes and tell us so we can help. There are plenty of things that can cause your issues.

 

I swapped out my NGK TR6s for my NGK TR55s when I pulled the blower

Only code it tossed was a MAP sensor code( low idle) which is why I changed it. It only threw it once so I think that is an effect...not the cause.

 

Did you zero your LTFT tables? If your tune was WAY off, it could foul the O2's before they pull enough fuel to get back in line.

 

How would I go about doing this ? Everytime I've asked these things on the EFI forums I get responded to with a bunch of acronyms and gibberish.

But again, would this occur with a stock tune with a baby cam? I ran the car for 9 months like that without issue. Though I suppose its possible I fouled up the sensors while trying to tune out the idle. Which may explain why its gotten progressively worse.

 

I'm not an expert on tuning. That cam is just a tad larger then a baby cam and requires a tune. I'll bet you need to have a tuner look at it.
ttt

 

Sounds like you have an issue with the MAF. Check it for being hooked up and make sure that its working. I up plug mine and see if it will work different in the Speed Density mode. The PCM will set a MAF code and you will be running off preset fuel tables. It will run but not very good. If your MAF is bad, doing this should change the symptoms. If it doesn't, it either already in speed density mode or you have another issue.

Check and post the DTC's.

BC

 

First off, are you sure your intake duct is attached to your maf? simple enough, and the first thing you should check.
Next, do you know how to use your scanner feature of your EFI live? If you do, fire it up and start the car and log some data. I dont have efi live, I have HPtuners, but its the same stuff, different flavor.
You need to monitor your map, maf, 02s, long term and short term fuel trims.
Is your maf registering a value of any kind at idle? If so, what is it? does it seem to fluctuate when you give it throttle?
Lets get some definite scan data so we can go from there.

 

thanks for the input guys

I've tried it mafless and tried it with the maf at different distances from the Throttlebody (have intake pipe laying around ) None of it seemed to make a difference. Even cleaned it with alcohal

I'll do some more logging and get back with results.

 

Ok heres what I got.

Ran fine up until coolant temp of 135. Both front and rear O2s seem to follow eachother closesly, so I dont seem to have one goofy sensor. They stay at .800v to .860 when its behaving. LTFTs at a steady -1.6% until the problem started

After 135 coolant temp the problem starts. O2s are spiking up and down from .525v to .890v . LTFTs are all over the place from -1 to -18% where it looks like they cap out.


So does this mean the engine wont run right in closed loop ?

 

Ok heres a good one. Once the car starts running like ***, if I turn it off and then back on, it runs fine again for a minute or two.

What would cause my car to say "Insert more coins" after a set amount of time.

 

Ok I forced it into open loop and it runs like a champ. Just took it for a nice drive with no hesitation no bogging no problems.

Any ideas why ?

 

The car is running poorly in closed loop only from what you say, since it runs fine till 135 deg and also when you restart, which is when open loop is active. Closed loop takes into account the O2's so you either have bad 02's or your tune is far off. As far as the LTFT's, I know EFI live has a feature in the scan tool portion to zero the long term fuel trim tables. I believe unplugging your PCM fuse for ~15-30 mins will also zero the trims but I could be mistaken on that one.

Open loop usually goes to your VE tables so they sound like they're ok...it sounds like 02 sensors and/or MAF right now. Possibly your MAF calibration table if that was messed with.

As far as your 02's staying "constant" vs "spiking all over the place" ....you WANT them spiking all over the place in closed loop! Normal 02's will cycle from .1 to .9 volts with sharp peaks and valleys....lazy ones will have curved slopes and won't go all the way from .1 to .9...they'll be closer to staying around .5 give or take a little. The oscillation of the 02's is what gives your pcm data to adjust the fuel trims....without oscillation, your trims will drift negative or positive depending on if the car thinks its running rich or lean.

 

Try turning of the long term fuel trims, then turn CL back on and see how that works. It does sound like it may be either a MAF issue of a faulty 02. What is the MAF reading at idle?
If your 02s are hangin around .800v OL, and when it goes closed loop they start to vary, and thats when your problem starts, you may have a mechanical issue that is covered up by the richer mixture, and when the PCM goes CL and wants to lean it to stoich, thats when it rears its ugly head. Vacuum leak is the first thing I'd be looking for.