What on my 89 controls the running conditions at different elevations. My car is modded with Mini, heads, cam and headers etc.
My tuner is in the Los Angeles area and set the air/fuel ratio right on close to sea lavel. The car smokes (hauls ***) down there. I live at 3600 feet and the car runs good up here, but when it idles, it loads up and idles rough. Just changed the IAC, and the old one was covered with carbon. Looked like the inside of a chimmney.
no codes!

Any thoughts?
Thanks

 

02 sensor

 

MAF sensor.

RACE ON!!!

 

The MAF reads the amount of air entering the engine and that will automatically compensate for elevations. To me it sounds like you have a tuning issue or a failed O2 sensor. Is the car in closed loop or open loop when you are experiencing the rich idle?

 

If the injectors are stock you might want to check the simple stuff first like change or clean the O2 as mentioned above. Wouldn't hurt to do some fuel pressure and resistance checks on the injectors since those Multecs have been known to cause a headache or two in the '89s.

 

O2 sensor has no "idea" what elevation it is at.

 

goofy o2 sensor don't know/don't tell elevation, but WILL cause rough idle/ surge/ and stalling...hook on a scanner and watch o2 sensor volt output, should 'toggle' above/below o.5 volts, if it hangs out at low or high end (~o.1= low/~o.9= high, most fail low) it's likely the perp, may tattletale a fuel ddelivery prob (injector drip, low fuel press, etc), if your o2 sensor is old go new and get better performance even if not the big prob...also look at CTS reading vs actual coolant temp (many go 'off calibration' with age, throw NO code, mess up idle and part throttle ops)

 

New Bosch 24 lb injectors with the build. Is there a test for the MAF? Visually it looks OK. I am not against replacing it, however, it gets expensive replacing items that are not bad.
I talked to the tuner and he said that the car was tuned and driven then tuned again. He does a lot of vettes and has a good name. He had five vettes in his shop when I picked it up.

I will replace the 02 sensor, and the coolant temp sensor also. I did read on here that if you unplug the MAF and the motor straightens out, the MAF is bad. When I unplugged the MAF the car would hardly run.

Thanks

 

Lots of things can make it run poorly. Fouled plugs, vacuum leaks, even a rag stuffed into the TB. Reread the OP if you want to help. The O2 can't be too far off, if "the air/fuel ratio right on close to sea lavel". Same with the ECT sensor. The ECT (CTS) doesn't go out of whack at altitude. The main question was, "What on my 89 controls the running conditions at different elevations." Also, note the title of the thread. While a faulty O2 sensor can wreck havoc with driveability, in no case is "the O2 sensor" the answer to the OP's question or his main problem.

Mostly, I suspect the tune. I am guessing that the relationship between the TPS outputs and MAF outputs are only correct at the altitude the engine is tuned at. More mapping needs to be done over a wider range of MAF/TPS combinations common at different altitudes to get the ECM to deliver the correct mixture for a wider range of conditions. Betchya!

RACE ON!!!

 

Don't throw parts at it! Especially every part everyone suggests. Trouble shoot it. Only replace defective parts, if any.

RACE ON!!!

 

I am also guilty of not absorbing the question and only offering a possible problem part, early morning brain fog.

But you need to re-read the post also.
Seems like the problem is at idle.


Are you staying in closed loop at idle ??

 

From what the OP states "setting the AFR ratio" sounds like the only tuning that was done is @wot. If that is the case, the rest of the tune will need to be addressed. All of the bin files I have seen for the maf ecm strategy there is no input for altitude available (in the original gm bin there is probably a table associated with the maf sensor itself, but it is not in the available bin files).
Regardless, it sounds to me like it needs more work in the tune. When dealing with modded ecm controlled cars you should be data loging it. That will tell you what you want to know (where it is rich/lean, spark knock, 02 sensor condition etc.etc.), everything else is a guess.

 

A "part" was what the question asked for. The O2 sensor just isn't the part that functions as the "Elevation sensor?"



Yes. But, only at altitude. The topic was, "Elevation sensor?" Also he said, "the air/fuel ratio right on close to sea lavel" and, "up here, but when it idles, it loads up and idles rough", which indicates rich only at altitude.

I have a friend with a way too large cam, and a DFI Gen VII ECM. It is speed/density rather than a MAF set up. It runs OK at 4500 feet through 5500+ feet, but when he gets to 7000 feet it runs pig rich at anything other than full throttle. I can tune an engine, but I don't know computers. I am 99% sure that the tune needs additional cells filed in for a more extensive array of MAP vs TPS combinations. It is my theory that when the ECM sees the lower manifold pressure of the higher altitude, it thinks the engine is under a greater load than it is, as it would be with THAT MAP at a lower altitude, and adds fuel.

RACE ON!!!

 

I need to ask my question again, is the car in open loop or closed loop at idle? In a MAF car 1989 design there is no tuning done for elevation changes, all of the correction is done with the MAS and the O2 sensor. The MAS will detect less air entering the engine and computer will caculate a injector pulse for that amount of air to run at the desired 14.7 AFR when in closed loop. The O2 sensor is used to correct for minor caculated fueling trim errors +- 15%. The TPS is used to help the computer determine the caculated load value for the engine which is turn used to determine spark and fueling conditions like WOT or closed loop operation (big operating changes). If the car is in closed loop operation at idle it could be a failed O2 sensor, or some other failed part like an injector. If the car is in open loop at idle then the open loop fueling table is incorrect and may have to be adjusted.

The bottom line is that if the car ran good in all conditions at sea level then it will run good at all conditions at elevation. My guess is it did not run good at all conditions at sea level or you have a failed part that you have not identified. With some more information we can identify what is incorrect or failed.