My 89 Formula with an LB9 experiences throttle lag but only after it warms up for a few minutes. (I am assuming after it switches to closed loop mode?). Basically when I first turn it on, if I press the gas it will rev immediately without hesitation. After a few minutes if I press the gas there is a noticeable lag, I can hear the air get sucked in, the RPMs drop slightly and there is a half second delay before it revs up.

I just replaced the fuel pump and filter a few months ago and it has good pressure at the fuel rail.

when I first got the car about 10y ago, i did all the maintenance stuff like plugs, wires, cap and rotor, etc. I also changed the O2 sensor around that time. But even back then it’s always had this symptom since I’ve owned it.

The weather is warming up and I’d love to finally solve this issue (or if this is normal for our cars I’d be interested in hearing that too)

thanks in advance for any suggestions

 

Not sure about 87-89's, but I do know on the 90-92, the accelerator enrichment (which effectively governs throttle response) is woefully inadequate in my experience.

After having driven some more modern cars and feeling the throttle crispness, the factory settings on the 90-92 presented what seemed like an extremely laggy throttle feel to it. I had to do A LOT of tweaking in the bin to get it where I wanted it. Granted my Miniram intake probably contributed to some of that, but still...

The only other thing I can recommend is to check your initial TPS voltage. After that, yeah, most likely in closed loop the ECM is pulling accelerator enrichment fueling out for emissions purposes based on O2 sensor response. Assuming all your ignition components are good quality and stuff like that, fuel pressure is good, etc...

In mine, I had to essentially tell the ECM to "butt out" for a second or two during throttle transitions, so it's not fighting me when I want the more fuel. But you can do that in the 90-92 code... not sure if you can in 87-89 (if this is in fact a factory calibration issue and you're up for changing it).

Lastly, you might want to get TunerproRT hooked up with a laptop so you can see what's actually going on with the running data. Could be something malfunctioning some place that you're not aware of.

 

Thanks ULTM, I checked the TPS a while back but I think it's time to check it again. I also figured that I'd try replacing the O2 sensor again since they're cheap enough and since the one in there was replaced by a shop over 10y ago. I ordered a nice Bosch one last night, who knows what the shop put in. I'm hopeful a quality unit will solve the laginess along with the extremely rich fuel smell. It's bad enough where if you're near the car for a minute while it idles you have to change your clothes. It would be great to kill two birds with one stone!

I've never gotten into the tuner scene, but it's something I'd like to try in the future. I didn't know that type of software was free either until I just googled it now.

 

I hate the factory replacement style 1 wire Bosch O2 sensors for our GM TBI & TPI cars and trucks.

What fuel injectors are in your car now?

 

Hah... I hated it so much, I bought a 4 wire.

It has the heater element for full length headers like your typical 3 wire, but it actually has a sensor ground wire too (hence the 4th wire).

The "O2 sensor ground" coming out of the ECM is just tied to chassis/engine ground, so it's only an "inferred" ground reference since the single wire O2 grounds itself to the exhaust manifold. It's a recipe for a ground loop if the electrical path from the O2 sensor body to the main engine ground point for the ECM isn't the greatest.

I tied that 4th ground wire back to the main engine ground so that the ECM now has a true O2 sensor ground.

 

Hopefully that improves things for you. Getting the operational data from the ECM would probably go a long way toward helping diagnosing things. Just need a laptop, an ALDL to USB cable, and the free TP download, and you're off and running on datalogging.

 

Yeah the heated 4 wire is what I like too, even for the factory cast iron manifolds. Heated O2 Sensor

 

I changed the injectors a long time ago, but I got the stock rated (19 lbs I believe for LB9), and they were Accel brand. It must have been 15 years ago at this point. I'm going to ohm test them when I get out there this weekend and recheck it's holding fuel pressure after shutting down just to check a few things off.

I had never considered installing a 4 wire sensor, thanks for linking that article Airwolfe! This might be a dumb question but what is the benefit compared to a 1 wire? After a 1 wire sensor warms up, aren't they essentially functioning the same way except the 4 wire has a ground? A dedicated ground is better than grounding through the exhaust but assuming there's no issues grounding on a 1 wire I would assume they are both essentially doing the same thing, no?

 

Thanks for the suggestion ULTM, I've never considered this route. If the new O2 sensor doesn't work I'll pick up the cable and see if I can figure out what's going on

 

Those Accel injectors could be an issue potentially. The if the electrical characteristics are different enough than the factory injectors, you could alterations in your fueling if the ECM isn't made aware of it via tuning. Not sure if you're aware of something called "voltage offsets". But it often varies from one injector type to another (even if they're the same flow rating). Typically results in leaner operation.

Do you have the P/N for those injectors?

The 1 wire will behave exactly the same as a 4 wire if the electrical grounding on the 1 wire sensor body is excellent (and by grounding, I mean from the sensor body all the way back to the main ECM ground point). All the 4 wire does is ensure the grounding is excellent (if you connect that sensor ground wire back to the main ECM ground), so you're not dependent on going through numerous bolts, bolted interfaces and varying types of (sometimes corroded) metal with electrical properties potentially varying over temperature.

In fact, if you hooked up scanner and watched the O2 voltage you wouldn't even be able to detect the issue... you'll still see the voltage bouncing around normally and think everything is hunky-dory. Just that the O2's ground reference for the voltage coming out of the sensor will be higher than the other grounds the ECM seeing, so the O2 will be sending an erroneous signal to the ECM. An erroneously low O2 voltage being seen by the ECM will be interpreted as a lean condition which will then cause the ECM to react by adding more fuel. And the opposite is true for erroneous high voltage.

 

PM me if you do. I generated a TP setup guide that has the strp by step instruction on how to get it up and running.

 

Interesting, I haven't heard of voltage offset but I will research it now. I may have the old box lying around my garage to confirm the p/n, it's a longshot but i'll check. If not, would this be something I could check using TunerPro? I will definitely PM you when I'm ready, thanks for the offer!

On the O2 ground, I'm not sure I totally follow what you mean. I thought the O2 just sends a value between .1-.9 to the ECM, and the ECM takes that value and adjusts the air/fuel mix. How exactly does the ground reference factor in? And thanks for all the extremely helpful info so far. I'm always reminded how grateful I am for the community on TGO every time I post.

 

Contact Holley for the 19#hr offsets. They don’t seem to be listed on their site. Here’s 24#hr just to show the data. 150819 was the p/n they had a old yellow and newer stainless looking body.

https://documents.holley.com/dfdb339...a9a0fbcda9.pdf

 

Thanks for sending that over! I just hopped off with Holley customer service. He said all the data (with the exception of flow rate) is the same for the #19/lb. injectors. That is why they didn't bother to create a separate PDF. Back to ULTM8, do you know if these voltage offsets look correct for an LB9?

 

Don’t know your bcc, this is APYM. Holley should really update their site if it’s the same 😝

 

Voltage is difference in electrical potential.... so the voltage coming out of the O2 sensor is the result of a small amount of current being generated by the sensor, traveling from the sensor element, through the sensor body, into the the wire going to the ECM, which then travels out the O2 sensor ground wire from the ECM to the engine, through the cylinder head, through the exhaust header bolts, through the exhaust headers, into the sensor body and back into the element.

Stuff in bold underline is the electrical path that the 4-wire can potentially improve.

The sensing element will generate a voltage in relation to the sensor body... but if that bold-underline path above is degraded, the electrical resistance increases and voltage that the sensing element generates is different than what the ECM will actually see because the ground reference the ECM is using to read that voltage will be different.

 

Thanks ULTM8 - in regards to what Tuned and myself posted on the injectors, do the values look right there? Admittedly i'm not clear on how to read these

 

I have one 5.0L bin for 89...

APYS 89 F-car 5.0TPI 5 speed with 3.08.BIN matches Tuned's values.

 

Thank you for checking that. Can you help me understand how to interpret this? If I compare the values at 8 and 16 (highlighted in my picture bc they are round numbers), it looks like the values on the Accel injectors I have in my car do not match Tuned's values. So what does that mean exactly

 

You need to look at the voltages that correspond to your actual operating voltage. You'll likely be in the 12.8 to 14.4V rows of that table which is where cars typically run at with typical alternator voltage output. The other table values don't really come into play unless you have a voltage issue with your alternator.

Basically when the two tables don't match, it means the ECM is not driving the injectors correctly. The ECM will drive the injectors to a calculated pulse width based on the various parameters in the bin (map, rpm, coolant temperature, MAT temp, etc). But the injectors will actually deliver a different pulse width.

For a general round number example to illustrate this.... if for given condition, the ECM commands a pulse width 1.0 ms, and the Accel datasheet voltage offset value is 0.5 ms (500 microseconds) greater than what's in your bin, the injectors will actually deliver 1.5 ms worth of pulse width. What'll then happen is the ECM will see a rich condition being reported by the O2, then start trimming the fuel leaner to compensate, and you'll start seeing low INT and BLM values until the ECM trims the mixture back far enough to get back to 14.7:1 AFR.

The opposite is true too... if the Accel datasheet value is less than your bin, then you get a lean condition at the O2 and the ECM trims fueling richer, raising BLM/INT.

 

I think I follow. So is it fair to say, the ECM will compensate for the difference in the Accel injectors voltage offset (assuming your O2 is working properly), and I end up in an okay spot as long as I get to 14.7:1 AFR? Or should I be looking into new injectors now?

 

IMO it’s easier to datalog and change offsets. These seem to work well and i think have a close to factory offsets. The D3 is another story.

https://www.southbayfuelinjectors.co...-firebird.html

 

In your typical operating voltage range, it seems that you're only off by about ~0.1 ms. Pretty minor. The ECM can compensate for that in closed loop. Other fueling subroutines that do not use the O2 sensor will be affected a bit... Open Loop, Power Enrich, startup, Accelerator Enrichment, etc... But I don't think it'll be that far off.

 

Agreed... if you want the greatest accuracy, you need to datalog and tune.

 

I had some time to work on the car this morning and have some updates:

- I tested the ohm resistance at each of the injectors, every one of them read 14.5, except one was 14.3
- I did a fuel pressure test, I primed the pump, and it held fuel pressure at 43psi for 30 minutes.
- I replaced the oxygen sensor, I attached two videos, one is a video of the tachometer while revving the engine, I intentionally stomped hard on the pedal so you can hear the delay between pressing the gas and when the engines revs. The lag is still there so I intend to look at the TPS next. You can even see the RPMs dip slightly if you look close.
- The second video is reading the voltage of the new, Bosch O2 sensor. The car seams to be running lean when it sits at idle. Any other ideas what might be causing that? The original owner put some fat conical filter on it that I never replaced. Could that be causing the lean issue?

At some point I want to get into datalogging, I just don't have a ton of time right now but that's next on my list.

 

Is the air filter an oil type ?

 

I'm more knowledgable about 90-92 Speed Density systems ($8D code) ...

But that kind of delay in revving... my suspicion is that's typical? It's probably a function of how fast the accelerator enrichment (AE) gets invoked. I know had to do a lot to my AE fueling in the calibration to get the kind of instantaneous revving that is more common on the newer cars. I've never driven a factory third gen car so I'm not 100% positive... just going off my experience with these systems having swapped one into my 2nd gen a long, long time ago...

In the $8D, there are all sorts AE lag filters, filter coefficients, etc that I had to hunt down and de-activate in order to get the instantaneous throttle response.

So my guess is with yours, there's probably some sort of a AE application delay in the $6E code. Not enough of a delay to cause hesitation during normal driving, but enough to cause this delay during a quick throttle blip.

In $6E there are a couple of scalars for mininum change in %TPS and LV8 (MAF reading) before the AE comes in, 3.91% and 20, respectively

If you stab the throttle, you're going past these values quite rapidly, but the throttle has already opened initially with no AE applied (until these thresholds are crossed), so the air is already on the way in by the time the AE fuel gets put in, hence the delay.

On mine, I reduced these thresholds to near zero, but even that wasn't enough because there were some obscure lag filters and other things that were working behind the scenes to oppose what I was doing. It wasn't until I found those and deactivated them that I get the throttle response I wanted. But that was only because I had the benefit of other folks having gone in and brought out all those other factors in $8D into scalars and such that are accessible in Tunerpro.

In the $6E code, there may be all sorts of AE factors and scalars that exist in the code, but have not been brought out to be accessible in Tunerpro.

So again, bottom line, this may be normal for factory cars of that era and not "fixable" without tuning.

 

And yes this kind of thing becomes more pronounced in closed loop and more warmed up. Probably the result of these lag filters and coolant filter coefficients in the code.

I was going through this a while go too... and it wasn't until about a few months ago that I finally figured it all out when I finally fully understood all these obscure factors in the $8D code

https://www.thirdgen.org/forums/diy-...e-neutral.html

 

You're probably right, it's probably just how these cars are designed and I should just enjoy driving it because it's running the best it ever has. But wow, I read through that thread and it seems there is a whole new world of information out there I need to get knowledgeable on. I'm not sure where to even start, is there a primer somewhere on this stuff so I can decide if I want to get involved? I have reservations about editing the code in my car's ECM. I worry obviously about breaking something permanently.

And, as always, thank you for taking the time here to help out. I really appreciate it.

 

https://www.thirdgen.org/forums/diy-...uide-book.html

 

Thanks for linking!

Last update, I just tested the TPS, back probed the middle wire with the key in RUN but car off. It reads .26 at idle/closed, and sweeps nicely, but only up to 4.2v. The range is supposed to be 0.5 - 4.5v I believe. Also, the meter consistently reads "OL" when I get up to around 1.9v for a split second. It's like there is a dead spot on the TPS. I attached the below from the manual in case it's helpful. Do you think the sensor is bad?

 

Adjust to .54, then might sweep again. It’s easier to see an open on an analog multimeter. Might get up to 4.5v at wot

 

So first, make sure you're getting the 5V reference out of the ECM by checking black to grey.

Then you should adjust your TPS to .54V per the manual (dark blue to black). If you're only getting .26V, that could be a problem. In 8D, if it gets below .41V, the ECM has some parameters in there that start doing some funky stuff. There may be something simliar in 6E.

4.2V, 4.5V, 4.7V, doesn't really matter... the manual says it should be "about" 5V. That said if you're detecting dead spots, the TPS could be bad. Just be sure it's not the voltmeter probes becoming intermittently connected with the sensor wires and giving a false failure.

 

I just went back out there, can confirm I'm getting 5V at the reference wire. I adjusted the TPS so at idle it's .52v. The lag/hesitation isn't totally gone but I would say it improved 75%. I can't tell if it's the TPS adjustment or the new O2 sensor I put in yesterday but between the two it's definitely improved. And the car's exhaust also smells much less. I haven't really been able to drive it much yet to have the ECM relearn everything so I'm hoping it will only further improve. I'm calling this resolved for now, and thanks again to everyone and especially ULTMT8Z!

 

Now get a xtreme aldl w/cable 1 and datalog

 

Glad it worked!

The other thing to do is to verify the IAC is set properly by going through the factory IAC reset procedure.