I have stock 89, and I would like to know how to have engine idle richer at idle. I don't have adjustable FPR

Injectors are bosh 3, I think 22lbs

 

What is your goal for making the idle richer? You don't really adjust the injectors. They are controlled by the computer software. You can have a tuner change the computers tune but that may not give you the results you are looking for. There are lots of other adjustments available such as TPS, IAC, Idle Set Screw and a few others depending on what issue you are trying to solve for. A little more information on what the problem is and we might be able to point you in the right direction.

 

Not sure why a stock 89 would need to have the idle richer ??

Vic

 

I have been working on getting my idle smoother. I have read numerous articles, some on this forum, that the 89 with 22 lb injectors can cause the engine to run lean at idle, causing an irregular miss. Each time the injectors were tuned to run richer at idle, the idle smoothed right out. I don't have electrical or engine mech problem, so I am thinking its fuel related

 

I doubt that all 26000 89 Corvettes produced had a lean miss condition. I would look elsewhere. They are programmed to idle at 14.7 afr.

 

Even if you got an Adjustable FPR, if the ECM sees it as being rich, it will dial it back by reducing the pulse width.

 

Not all, just seems to be on SOME that switch out stock injectors for bosh 3 injectors Something to do with flow rating

 

But even if it flows more, I think the ECM will compensate and reduce the pulse width. Maybe it runs better than before because of the placebo effects and/or that the old injectors were crudded up

 

Would it be easier to just get rid of the Bosch injectors?

 

Might be easier to reprogram the EPROM to dump fuel.

 

There are some ways to accomplish this...but mostly if it's really lean enough the computer can't correct. For the most part, there's about 15%+/- error that can be corrected (BLMs) if you're "off".

First off, I'm going to say....If you don't have a Moates adapter and chip, you can't do ANYTHING. With tuning software, you can just monitor/diagnose what's going on!!!!

I was thinking Jon did something to "fix" that Bosch III injector issue after the first few people began buying them 5+ years ago? Did you buy from him? Really, that doesn't matter. IIRC, they were a hair lean (for the factory BIN), if they weren't slightly opened up. (But, I'm going on a 5-yr-old memory!!! And, I'm OLD!!!! LOL)

If you really have the stuff to burn a chip, start by setting the Single (and Double) Fire FI Size @ 40psig to your 22lbs.

Injector Pulse Width Correction versus battery voltage can also be set -- if you have the voltage curve from the manufacturer.

Finally, monitor the idle rpm. I think you'll be looking for MAF volts. That's the lookup value for the MAF fueling tables. If you raise the value at the idle voltage, you'll idle richer -- but mostly if you really are too lean.

Other posters are correct that BLMs are used to "write" correction data for the computer so it can compensate for where it's rich/lean. That's primarily why the computer monitors the O2 sensor....to look for rich/lean at any rpm.

There's also an 02 Error reduction gain vs Airflow that might have an effect -- because the rows only go up to 64 grams/sec. That's obviously the lower fueling rows...

Closed Look Rich/Lean Offset also can provide some control over exact AFR if you have a wideband and know what you are doing. Actually, I would call that true for both these last two parms.

Again, the computer WANTS to force an AFR to "stoich" 14.7:1 AFR. It has the ability to correct fairly large errors w/o help. That's why MAF systems are so "easy".

If you are going on the color of your plugs, it may be you need a cooler plug. If you just heard/think you are too lean (especially at some random rpm), you aren't making the best decisions.

With tuning software, you "program" proper AFR during closed loop 02 monitoring. During open loop (warm-up/WOT), you'll need either a wide-band, knowledge of narrow-band 02 readings, and/or some very good assumptions based on the mechanics of your alterations to make changes that are reasonably close to workable.

 

LOL...Getting those suckers out from under a TPI ain't no picnic, is it!?!?

 

Way easier than a Superram unless you mod the box to take screws from the top and more difficult than a HSR.

 

Thanks good info. I just got them back from FIC. Had them gone thru. I do have Moates equipment.

 

I think a quick test would be to just pull the vacuum line off the FPR and plug it. If I remember correctly, that will increase the fuel pressure slightly at idle. It'll take a moment for the computer to respond so if your idle smooths out, that's the right direction for re-programming.

 

FYI: I don't like that I said you can program proper AFR during closed loop. That's misleading.

People have told me you can monkey with the Rich/Lean Offset to effect a change...but the computer constantly searches for...and corrects AFR by monitoring the 02 sensor. Normally, that "offset" is the swingpoint between rich/lean. Adjusting that swingpoint is what favors a mixture on one side or the other.

And, the mixture isn't necessarily 14.7:1. When you change from pure gasoline to "gasohol", the data sent by your O2 sensor allows the ECM to compensate. E10...which seems most common these days, has a stoimetric of 14.1:1.
Here's a good article on the topic.

Alcohol requires more fuel/air than gasoline. That's why you see lower mpg with gasohol versus gasoline. (This PLUS the swap in injectors MIGHT be contributing to any lean condition you are seeing.)

For extreme situation (like running E85 as an example), you might be forced to setup a bin for total open loop operation, use a wideband to tune, and be precise enough that the O2 sensor isn't used anymore. If you do this, you can program anything you want.

 

I just thought of another way you could accomplish (test?) a leaner idle mixture. (Or...any RPM is you really wanted to...)

Set the Minimum Speed MPH for Hwy Fuel Mode to 0....then
Adjust "Highway Mode Air/Fuel Ratio vs LV8" to a leaner mixture.

If you set the 32/64 rows to 14.7 (as an example), that should do it. With pure gasoline, it should force you to run stoich at idle...or, if running 10% gasohol, you'd be lean.

You probably don't want to force it "lean" at idle because cars don't idle as well if lean. Stoich for 10% gasohol is 14.1 AFR. I've never heard that anyplace has gone to 15% yet. May never get there either.

 

Bosch injectors are an approximation to the OEM units, and may have a different "transfer function", the input versus output of the injector. I replaced the injectors on my 1990 with Delphi OEMs and the car runs GREAT. Not surprising, as the entire system was designed at the factory to run with the OEMs.

My two cents, but I'm guessing if you put the OEM injectors in, your idle problems will go away. The Delphi OEM injectors are a bit expensive, but my factory injectors lasted 26 years and 90K+ miles before needing replaced. When I put the OEMs in the car was like new again (well, once I also replaced the coolant temp sensor, but that's a different matter).

 

Not sure I follow. If your fuel pressure is X psi and the injector flows at Y cc/min and you have Z ms of pulse width, how does one injector differ from the other in any significant way?

Delphi? I don't know if the injectors they make are like the ones they gave us which cool the coils with fuel and get eaten by the ethanol but if they are different, how can we be sure that the spec is the same anymore? You could be getting a new "equivalent" unit.

 

Injectors should have characteristic curves that vary slightly from one brand to the next. I got my OEM Delphi units from a Corvette shop that replaces injectors regularly. They told me that in their experience, using other than OEM injectors can create idle and other issues. Not a big deal, but there nonetheless.

Ethanol fuels existed in the 1980s and onward. My OEM injectors from the factory lasted 26 years before at least one failed open and let too much fuel pass. Could even have been a clog or varnish build up for all I know. But 26 years is good enough for me. Maybe OEM injectors from the 1980s and 1990s fail from ethanol eating away the wire insulation, but I doubt it. If that were the case, millions of cars would have had failing injectors, and either a recall or class action suit would have ensued.

To each his own, but I like to go with OEM equipment when possible, since that is what the car was designed, prototyped, tested, tweaked and produced with. My two cents...