I have been running a tune for about 3 weeks with no problem, except for WOT. I wanted to scan the car yesterday, and work on the tune this week. I plug in my laptop and start datamaster. Connect my LM-1 to monitor MAF, TPS, RPM, and Wideband O2 sensor. Start the car up and like a switch it is running terrible. Stumbling and hesitating. It was bad. Anyways, now I dont know what angle to attack. I checked my fuel pressure thinking the AFPR went south, but it was rock solid at 40 psi with vacuum removed. Fuel pressure dropped as vacuum was applied. I am getting no codes. I have the occasional pop out of the exhaust, and when i put it in the garage, my eyes burned from the fumes!! So what do I attack? I'm running an MSD 6AL with MSD wires, all probably two years old. Plugs about two years old. I will check the MAF operation tonight, but I would think it if were malfunctioning I would have a code. Thanks, Craig

What are the BLM's looking like?

Are you going into closed loop?

I will look at that tonight after work, and make sure it is changing from open to closed loop. I unplugged from the laptop thinking it may be creating an issue. The LM-1 as I glanced at it was less then 12.5:1 pretty often under light load normal cruising.

I don't have a reference as I have not scanned with this tune before. Now all I need to do is wait for work to end!

Thanks for the response, and I will get back.

Craig

I am definitely going into clsd loop. In datamaster I am saying Lterm fuel counts is BLM, and Sterm fuel counts is INT. At idle BLM is pegged at 160 most of the time and the INT is 130. Occasionally BLM will come down into the 150ish range and INT still 132.

I did all this just sitting in the driveway. RPM steady 2300 Load Var at 50, BLM is 118 and INT is 128 ish. RPM at 3500 Load Var at 60 BLM is 120 and INT is 119.

I will attach a PDF file of datamaster log. I would be more than willing to send the files to anyone.

I also attached a log file from my LM-1. I am recording AFR, RPM, TPS volts, and MAF volts

Thanks in advance for the responses and help, I really appreciate everything.

Thanks,
Craig

My idle is rougher. Not like a huge cam, but rougher than usual. We all know how are cars feel and sound, and mine sounds rough. It has a hesitation that was never there before. I am just wondering if i don't have a plug or wire problem.

My TPS voltages look suspicious in both files. I am humming along at 1500-2000 RPMS and volts are between 2 and 2.25, then 2300 to 3k it decreases down to .62V ??

Does anyone have any suggestions. I am not a very proficient tuner yet, and would like to get this fixed so I can play again. I am thinking it isn't the tune. it may not look the best, but it did run for 3 weeks. i am wondering if a sensor, or plug/wire is bad. No codes though, even when I connect with datamaster, no codes.

Thanks,
Craig

Im not very proficient by tuning standards aka "noob", but I
could diagnose whether that TPS sensor is the culprit with a 5
dollar voltohmeter. Voltage should progress smoothly all the way
to WOT, from my understanding.

Worst yet, you could always buy one real quick.. test it out,
if it dont work.. make sure she is clean and shiny and get your
cash back!

But a hot/bad TPS could explain a rich pig symptom.

Based on my past logs what you are looking at is a classic peddle stomp,
Air flow lags the TPS a little and follows RPM.

If you have a tps issue it should be tested at a steady speed, or key on engine off and slowly press the go peddle while watching the tps volts by meter or logging.

The ramp up and down should be smooth with no jumps.

I kind of expected that answer, after I posted, but couldn't be too sure. I should be able to test my tps using datamaster. i have used paper clips pushed into the connector with a DMM before.

Is there a preferred way to test the MAF?

Thanks,
Craig

Just tap on it and see if the engine stumbles or just unplug it and start the engine, if it runs better then Maf is bad.

Check the burn off, power relays, and check for bad/loose connections.

Try to find a known good one and swap it out.

I have bought rebuilds that were bad from the start (AZ).

You can also get them tested/rebuilt, it cost me $80.00 last summer.

I own more then one MAF/TPI so testing is easy, swap and data log. If the trouble moves, it is the MAF.

Sounds easy enough. When my brothers car was running bad, his would actually not idle well at all, we unplugged the maf, and the idle returned close to normal.

I will try this. I have to start leaning towards a sensor, electronic component, or a plug or wire.

Thanks for the help!

Craig

I would guess, based on what I've read in this thread, that your tps is bad or out of adjustment. At idle it should be around .54 give or take and then smoothly progress to
4.5-5v at wot

I am going to look at my TPS sensor.

My brother came over to give me a hand. I went and purchased new plugs. They all looked about the same, so that was a let down. I figured I would find one that was noticeable fouled.

So as we were putting the plug wires back on, he says well I found your problem!!! I was like whatever, he says no look. Sure enough, #7 plug wire had come loose out of the connector and was laying against the header. So I unplugged that wire and the car ran the same. While it was unplugged the spark was jumping out of the bad spot in the wire. He ran home, pulled one of his wires, we put it on, and problem solved.

Thanks for everyone's help. This was another learning experience. Check the simple things first. I wanted to, but just didn't think it was.

Ironic! I let my sisters boyfriend borrow one of my wires for his
'79 pickup.. Well when I got it back, I forgot to connect it to
the plug!!

I wondered why my car was so dam rough those few days,
then I finally saw it dangling!! ...gotta love when its something
so simple its stoooooopid!

I agree. This is a good lesson. Always start with the simple stuff, and have a method or procedure of sorts before guess work. I always thought that is how I did things, until I needed to actually do something.