runnin rich

[97z28swap]

my 97 lt1 i running rich. I brought it to the dyno and put a (sniffer) air fuel ratio gauge on it and it said i was running about 10.1. should i get an air fuel controler to lean out the mix or is there something else i can do thanks

[fastTa]

Did the dyno operator allow your car to fully warm up before he sniffed it?

The reason I ask is because until the O2 sensors fully warmed up they are not providing the PCM with accurate values. Essentially the PCM is having to do a lot of guessing in this version of open loop mode as to making the correct injector pulsewidth. Even though the PCM knows that the O2 sensor values are not yet correct, it still will try to make an attempt to get the correct pulsewidth, however it can be pig rich in alot of cases.

If the motor was running in this version of open loop at just moderate loads on the dyno, the PCM would have used the AFR table for the injector pulsewidth determination. The AFR table uses the ECT and MAP values to get as close as possible to the desired AFR under your load conditions and temps on the dyno. So with the MAF sensor values telling the PCM how much air is being inducted, and the PCM reading how big the injectors are, and the value of the AFR from it's corresponding table, the PCM will do it's best to approximate the correct pulsewidth. But it will usually be rich. Cold motors nees to be run rich anyways.

The AFR is fixed at 14.7:1 in closed loop mode where the 02 sensor values are not used for fuel trim correction.

Even if you were running in power enrichment open loop mode their was a good possibility that your O2 sensors were not fully warmed up. The LT1's have been known to run a little rich from the factory, but 10.0:1 is very rich and it a little out of the range for norm.

[97z28swap]

rich

yeah the truck was warmed up all 3 runs. and they were all about 10.0.1. plus the snifer was warmed up too i was the 3rd one on the dyno and it was on from the 1st car

[fastTa]

yeah the truck was warmed up all 3 runs. and they were all about 10.0.1. plus the snifer was warmed up too i was the 3rd one on the dyno and it was on from the 1st car

The LT1 PCM can be re-flashed to correct the inherant LT1 rich factory programming. Your dyno place should have the software to do this.

But 10:1 is very rich. Even beyond the normality of what the stock LT1 program usually runs at. This is why I asked if the car was completely warmed up. It is possible you have a faulty MAF or a faulty o2 sensor. Their are many factors that could cause a rich condition such as yours. The only realy way to narrow the problem with the A/F is to get it on the wideband and a scanner and start tuning.

How familiar is your dyno place with LT1's?

[Injuneer]

Are you running the PCM from the 97? If so, get AutoTap on it and log a variety of operating conditions, from startup through cruise through a WOT pass. You can get some insight by looking at the long term fuel corrections, and other sensor data that might indicate a source of the problem. I would recommend a scan and analysis, before trying "reprogramming". I would estimate if you really had 10:1 A/F ratio (that's actually the lower limit for some wideband setups... as rich as it will indicate), you are running about 17% richer than the typical stock PE mode target A/F ratio of 11.7:1. You need to figure out what is causing that... bad O2 sensor data, excessive misfires, leaks in the exhaust system before the O2 sensors, etc.

Where did they put the wideband sensor? Did it read one side of the engine, or both?

[97z28swap]

rich

the dyno never had an lt1 on the dyno so he doesnt really know about them too much. the sniffer was on the drivers side of the engine and it is true duals with no connectors in the exaust. plus when i was on the dyno you could tell it was rich just by the smell of it. I had the tech 2 scanner on it a couple of days ago and it seemed that all the o2 sensors were sweeping fine like they were reading right. oh yeah i dont have air injection anymore how much would that make a difference in the sniffers readings

[Injuneer]

AIR has no affect whatsoever on the A/F ratio readings.... the pump only runs for a few minutes at startup to help heat of the cats, then shuts off.

Are you able to compare left and right bank O2 sensor readings at WOT (rather than at part load, closed loop)? That would give you a rough idea if the "problem" is on the drivers side only, or on both sides. You also need to look at the long term fuel corrections to see if it is "adding" fuel at WOT, since there are times when the PCM uses Cell 15 for WOT, and the long terms in that Cell, and other times when the PCM defaults to Cell 18 and locks the long terms at 128.

A scanner, like AutoTap will also show the "target" A/F ratio that the PCM is calculating in PE mode, using the tables Kevin mentioned.