I'm trying to work through a list of problems with my car. I finally figured out that the fuel pressure regulator was completely shot and replaced it yesterday. Now the car runs for the most part. However, it's not running well. The idle is too high and more often than not, it stalls while in gear unless you are giving it a little gas and is hard to start when it gets hot. Last night it seemed to run mostly normal but today it was all over the place. Didn't want to stay running in gear unless you were on the gas a bit, but will stay running in park and neutral. Likely due to the rpm being too high. While there are a number of codes stored in the computer, they are the exact same ones from the last log I have some years back, so until I delete them and run the car a bit, I'm not sure if any of them are current. For what it's worth, the codes are 13, 14, 15, 21, 22, 23.

I got the laptop hooked up for a quick log file. It was in park for about half the log, then I had the AC on and had it in drive and reverse once the car warmed up for the last half of the file. It decided to not stall this time. I have a tunerpro csv of the log I am trying to go through and would greatly appreciate it if someone here would have a look and tell me what they think is going on and going wrong. This is for a 91 trans am, 305 tpi.

 

Is it stock? What injectors?

 

Stock. I replaced the injectors some years back from the stock multecs to svo 19lb injectors.

 

Do you have a part number on the injectors?

 

Hang on... I checked my old posts and I believe this is the part number of the injectors, FMS-M-9593-C302. I can't be 100% certain, but I do believe that's the number.

 

Ok good. There is injector data.

https://r.search.yahoo.com/_ylt=Awr9...wgdd48VxXBBQs-

Can you post your bin as well?

 

I'm using this. Did you need the definition file as well?

 

Have you done any chip reprogramming? Its the bin file i was asking about. If not I have the factory 305 bin.

 

No, nothing at all. Complete factory although the ecm was replaced at the chevy dealership about 12 years ago.

 

Any way to get the broadcast code off your PROM? I.e., is it AWFU? AXXD?

Also post the native .xdl log file?

Also, can you take data using this definition file? You'll have to rename it to .adx. I had to rename it to .txt so I could post it here.

 

I'm using an older version of tunerpro so the log is in the adl format. I'm not sure on the broadcast code. I'm looking at the log replay and the only prom listing is for the prom id which lists it as 20E5. I'll toss up the original adl file.

It wouldn't let me upload it here in any format, zip or otherwise, so here's a link to the file. https://gofile.io/d/JuDdhM

 

I'm guessing I wouldn't be able to use that adx file unless I install the newer tunerpro and run a new datalog?

 

Here's what I'm seeing... though the dataset is pretty limited

Your idle speed is high with (for the most part) 0 IAC steps, indicating the engine is getting so much air from another source that the idle air control motor doesn't need to do anything... so much so even that you're idling a few hundred rpm higher than the prescribed idle speed.

Two possibilities... a bad vacuum leak, or your throttle blades are open too far.

Other issues..

your BLM (long term fuel trim) is a little lean. It's not terrible, mid 130's to low 140's. This could be a result of your factory injector voltage offsets being a little off from the injector datasheet. It could also be a result of low fuel pressure. I don't know what condition your fuel pump is in, or your fuel filter, or your pressure regulator. The other thing is whether this amount of lean-ness is consitent across other rpm's and and engine loads. If so, and your fuel pressure is good, my guess is it's injector voltage offsets, in which case the solution is to burn a new chip with the correct offsets per the datasheet.
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You're also getting knock counts at idle which is unusual. Could be an issue with your knock sensor.

 

Let's see what I can add. The fuel pressure regulator was replaced yesterday. It had been running on a bad regulator for a long time and I didn't know it until I disassembled the thing. the fuel pump is only a few years old and is a Bosch 69218. Fuel filter is older, so not sure of the date of that.

There is one vacuum leak that I know of, but it's from the vacuum reservoir to the T connection next to the washer tank. I'll have to have a look at the throttle blades and see what's up. Maybe the throttle cable is out of adjustment due to me unbolting it from the plenum a few times so I might need to reset that. I have another throttle body I can toss on if need be. As for another vacuum leak, I didn't see anything obvious attached to or near the intake when I was working on it yesterday. I may need to buy a can of ether to spray around and see if anything affects the idle.

This was also just a parking lot datalog. I'll need to run a better one while actually driving.

Oh, I will also put a fuel pressure gauge on the rail and see what readings it's giving me.

This is a lot of new information for me, thank you very much.

 

Yeah see if you can get these items resolved and then see where you end up.

 

I decided to do a drive datalog before messing with anything to get a better base of data to work from. It's about 15-20 minutes of driving, idling and running the AC during idling for a bit. Once I get the laptop going, I'll upload the log.

 

See if you can get the latest tunerpro and use the adx file i posted.
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Also remove power from the ECM to clear all the old codes.

 

I'll do a new datalog with the new tunerpro after this next fiasco. Would a failing o2 sensor cause any of these problems? I believe mine just failed spectacularly on the way home on a 2nd trip out today. Car started running like trash, SES came on, got worse and worse where it would barely stay running. Like crawling the short distance back home as it barely stumbled its way. I pulled the code and the only one in the computer was 44, oxygen sensor. If it has failed, and due to it not being old, I "guess" the failed FPR dumping gas like it was free into the engine slowly started killing the 02 sensor and it just decided to fail today. I think the gas gauge started going down a bit after the failure started, but I was barely looking at that at the time. Does that sound reasonable?

 

Alright, new o2 sensor in and I got another datalog on the new tunerpro. It's an idle one as its too late on a Sunday to be driving around and worrying if it'll fail before I get home. Car runs no better or worse than before the o2 failed, which is good at least. Had it in drive, reverse and the AC on at one point. It did stall halfway through as I had the AC on and was revving it and letting off the gas and it stalled on one of those. I did pull the battery for a bit while working on things so the ECM should have wiped any codes.

Looks like I'll need to rename the xdl file to upload it here, so just changen it back from txt to xdl.

I was watching the o2 sensor readings and they seem very different from the old one. The old ones readings seemed to vary anywhere from 4 to 800 or so and were all over the place. With the new sensor they stay within a fairly narrow range when fluctuating. Not sure if thats an issue with the older vs newer tunerpro or something else.

 

I'm not seeing any codes being thrown, so that's good.

Yeah, what seems to be happening is you're falling out of closed loop. I take it you're not running headers? Single wire O2's are notorious for cooling off in headers to the point where they allow the ECM to fall out of closed loop, particularly at idle speeds.

Were you able to check the grounds on the back of the heads as GeneralDisorder recommended in the other thread?

Your O2 voltage range across the entire data log is 124mV to 566mV. The rich/lean indicator stays "lean" throughout the whole datalog.

For the brief period you went into closed loop, BLMs climbed to 145 (lean) at which point it went back into open loop.

The curious thing I saw is that when your engine died, and just before you restarted it, your O2 sensor was reading 566 mV. When I turn my ignition on, my sensor reads .450 mV, which is what I think they should be reading with the engine off. I'm not sure if your 566 mV result of residual exhaust gases in your exhaust pipe or not. Maybe after letting the car sit a while, turn on the igntion and take not of the O2 sensor voltage.

But, as of now the data does seem to be pointing to some issue with your O2 sensor. What brand and p/n O2 did you get?

 

No headers, just the stock manifolds. The thing is, the car is running the exact same now on the new sensor as it did on the old AC Delco sensor. It also ran, for the brief period of time that I ran it yesterday, after the failure, exactly same with the sensor disconnected completely. The sensor is whatever amazon had that they could deliver in one day, ummm, Kaz brand. Looked pretty solid at least, but no idea on the brand quality.

Since it's having issues from dead cold and even with the sensor disconnected... I did replace the missing vacuum hose from the reservoir to the T before the cruise control which didn't do anything. Interesting enough, for about 2 or 3 minutes before I could get tunerpro to connect, the idle was lower. This was from dead cold. However it still was bouncing around unstable still. It then moved up to the higher idle you saw in the log. I need to check fuel pressure later when it cools off as I need to pull the map sensor out of the way to get at the valve.

Would something funny with the IAC cause the excessive air intake that you were seeing before, even from a cold start? Like it it was stuck open, closed, clogged, something? The throttle blades seemed to be fully closed when I checked. If there's a high idle and random stumbling with the sensor disconnected even, that has to be something else other than the sensor, right?

 

Ok, so let's back up a little...

You may have a few issues going on simultaneously...

High idle - start with the basics.

Simplest thing to do first... Run through the idle speed setting procedure first. https://www.thirdgen.org/tpimod2/

If that doesn't work, check everywhere for vacuum leaks. Trace down and inspect all your vacuum hoses. I think at a minimum, all the engine needs to just run at idle is the MAP sensor and the fuel pressure regulator. So you could temporarily disconnect everything else and see if the high idle goes away. Of course, make sure the vacuum lines to the MAP sensor and regulator are known-good. If this solves the high idle, simply start connecting one other thing at a time and see what causes the high idle to return. The leak could be coming from one of many places.... power brake booster, PCV, EGR, charcoal cannister, or some other device or accessory that runs on vacuum.

Fueling problems...

The business of falling out of closed loop is an issue. Whether the O2 sensor is the problem or not, the loop status changing is definitely A problem that needs to be resolved. You definitely need to validate the wiring and grounds. The entire O2 sensor circuit needs to be good, not just the sensor. If you have some electrical capability and a multi-meter, I'd ask you do drop the ECM and backprobe the O2 ground wire to see if the ECM is actually seeing ground on that wire.

Another thing to do is to take a multi-meter and measure the resistance from the O2 sensor body to the negative battery terminal. If you get more than an ohm or two, you'd want to clean up the exhaust manifold where the O2 sensor mounts to. The O2 ground at the ECM is only a reference. The actual ground for the O2 sensor is through the body of the sensor to the exhuast manifold.

I think you need to get these issues resolved first. Need to get the known problems resolved so the true culprit can be isolated (if it's not related to these).

 

First, a side note.

When heated up, the gas tank creates pressure, but, the vacuum canister purge valve is... hissing? making noise? Its making some kind of very audible noise until I undo the gas cap releasing the pressure. Not sure if that's related, but figured I'd add it in.

Alright, this is an excellent to do list. I'll pick up a can of starting fluid to check for vacuum leaks. Every hose I've checked seems to be in good shape, even the hard lines. But starting fluid should confirm or deny that bit. The electrical I can do. Just need to sort out which pin is the ground for then o2 at the ecm and where the other end of that goes to. Can easily test the sensor body to battery. The manifold is fairly rusty look as they usually are, so that could be an issue. I was only able to check the passenger ground from block to firewall and that one was ok. Rain stopped me from doing much else under the hood earlier.

 

In the picture below (an old hacked up connector I had in my parts box)... the indicated wire is the O2 sensor ground. You have to take the plastic clip off the connector to get at the terminal inside, but take a multi-meter to measure the resistance between that terminal and chassis ground. You really shouldn't have more than a few milli-ohms of resistance if the wiring is in good shape.

 

Sounds like you may have a tank venting issue too then. Again, one thing at a time here.

 

I went out to pick up some starting spray and throttle body cleaner. Figured I'd run the logger, and of course it decided to not connect at all, so I'll need to figure out what I did wrong. It gave me issues the day before and then just randomly connected while I was looking at settings. At least the car ran today. As well as it has been so at least I can now begin to check for vacuum leaks, clean the throttle body and iac and check grounds...after it stops raining.

 

Ok, got tunerpro connected again. Think I worked that issue out. Just did a quick look with the key on only. tps is sitting high at .80 but since its a non adjustable tps, I assume I'll need to adjust it via the adjustment screw on the other side of the throttle body. I did move the lever on the tps and it went up to around 4.18 so it is working. I don't know if I ever messed with it when I replaced the TB, but the protective cap is gone, so who knows. That should solve the issue of high idle/rpms once I adjust it some. However, I doubt it will solve the stumbling/stalling issue. I wonder if one of the shops that worked on the car some years back bumped up the idle using that screw to keep it running. Not sure, but if I reset it to .56 first it may make the idle/stall issue worse until I work out why its stumbling in the first place. I'll probably adjust it to see and if I need to, bump it back up so I can keep the car running while I look for leaks and stuff.

The o2 sensor was still reading that 565 reading with the car off you saw on the log, so not sure if that's an issue or not. I'll tag that as a secondary problem after working out the idle speed and stumbling.

 

Resetting the TPS won't help with the idle speed. Everytime you start the engine, ECM looks at the TPS setting and establishes that as zero for that run. As long as you're getting a ~4.5V swing from idle to WOT and it the voltage moves smoothly, the TPS is fine.

Running the idle setting procedure I linked to should establish the correct throttle stop screw setting.

The .565V reading on the O2 sensor just doesn't seem right to me. Pretty sure the O2 should be at the center voltage of 450mV when engine is off, which means the circuit has some sort of ~115mV offset to the rich side. Granted we're talking narrow band (not wide band), so the amount of voltage away from 450mV isn't indicative of an actual air fuel ratio, But if there is a .115mV fixed offset to rich, the ECM will definitely react to that and start leaning out the fuel mixture. Which probably explains why I'm seeing the BLM start climbing (at least when the ECM is in closed loop). You also still have the issue of dropping out of closed loop too... You can also run the engine with the ground wire on the sensor to see if the ground is also a culprit for this too.

What you could do here is ground the sensor body to chassis with a wire and then look at Tunerpro. Could simply use a hose clamp to clamp the wire to the sensor body and then run the wire to the engine and/or the negative battery terminal. If the voltage gets back to normal, then you likely have a grounding issue with the sensor body.

 

Yeah, I was just looking at it as the tps lever is controlled by the throttle so if the tps is reading high it likely means the throttle is adjusted too far one way pushing on the tps lever giving it that higher than normal reading. So I guess the correct thought would be that the throttle adjustment is incorrect and resetting that to get the iac/idle in order will get the tps reading back in line. I'm not sure it went to 4.50, but I did see at least 4.18 or so. I'll take a better look when I adjust things.

Can the volt meter be used to ground the o2? Just a thought.

 

incorrect throttle stop screw could be the source of the high tps voltage, yes... as well as the idle speed. Assuming the tps was set to the correct voltage prior to the stop screw going out of adjustment

The multi meter won't ground the sensor body. You'll need to ground it.

 

Cleaned the throttle body and iac which were fairly dirty, then tested the car and no change. I then decided to check the fuel pressure. Key on, pressure is at about 41 psi at idle. Key off and the pressure starts to drop. Within a couple minutes or so it was down to 20 psi before I put everything back together. Didn't mess with the idle speed reset yet. Way too hot out there and needed to stop for now.

 

I hadn't had any time to work on this till now. Car got progressively worse. Serious stumbling, like it wasn't getting any fuel, then it would kick in and be mostly ok for a bit. Very hard starting. Lot of cranking needed to start. When the problem first got really bad this week, it threw a couple codes when I pulled into the lot. 15 and 44. As I had a new Delco CTS sitting around for years, I decided to install that and replace the already replaced O2 sensor which I was leaning toward it being defective. Got a Denso this time and that seemed to solve a lot of data issues, but not any running issues.

Car goes into closed loop now and at least for a while, bounced normally between lean/rich readings. Took it for a very short drive, i.e. maybe half a mile total. It ran well for the first half. Got to a stop sign, took off and it stumbled horribly. Would barely move for about 200 feet then it picked up some steam and I got home. Datalog shows the point where I stopped at the sign and that's when the O2 sensor started reading extremely lean all the way home from that point, going back into open loop around that time.

So, I solved some issues with the replacement O2 sensor for the defective one. No idea if the CTS sensor did any good, but its new at least now. Car is now unsafe to drive as is and I'm at a serious loss, as usual.

I uploaded the datalog from this run. It needs to be renamed back to an xdl file as I had to change it to txt just to upload it here.