I just fixed my random extreme rich condition. I was max out negative on stft and was getting -18 on ltft intermittently. I figured it was maybe my maf or o2’s are bad. I have HP tuner and switched to a SD tune (runs with no maf or o2’s) and was getting the same problem. So I connected my laptop HP tuner scan tool to monitored any changes. So with the ignition on but motor not running I started to wiggling the wire harness/ connector for iat and ect temps, throttle body, and map. I found I had a loose or poor contact on the map wire harness connector pins. My reading went from 88 Kpa to 103. The female pins lost their spring tension so dissembled the connector and bent the them to have better contact... and no more problems. Hopefully this may help you out. Good luck.

 

How much does the fuel pressure fluctuate during idle ??...what about higher RPM...when the key is turned off does the pressure drop suddenly ??...this video may help with your Tech 2...it is not the most user friendly scan tool platform...I think it’s the worst !!...once you can graph the O2 let us know...one snapshot doesn’t tell us much !!

 

Your surging is caused by the large swing between what the cars AFR is vs what the computer wants it to be. The car is commanding 14.68 AFR in closed loop. But your car is running way rich for that to happen. It's the large swing in AFR that the computer is trying to correct that is causing the surging. Until you get the AFR closer in line to what the computer wants to see it will continue to surge. When you start the engine up cold it is in open loop so no computer corrections, so no surging. But once warmed up surging happens because it goes to closed loop.

Question on the new injectors that were installed. How long ago did you install them? Did you mention the year when ordering them? Different Pound injectors came in the 99-00 C5s than the rest of the C5 years. The 99-00 year C5s had 26-pound injectors while the other year C5s had 28-pound injectors. If you put in 28-pound injectors in your car it will always run rich. That could be a contributing factor here why it's running rich. Also, an unbalanced set of injectors can cause all sorts of issues. If there is a number you can read on the casing post it up here.

As far as vacuum leaks, have you put a vacuum gauge on the car?

As mentioned, need to see the O2 live data. Odd that the one bank is getting all the misfires. Car is running rich on both banks.

 

Here is the O2 live data. The downstream sensors look stagnant. I did check the fuel injectors and they all measured the same drop, 52psi to 29 psi. The video of the fuel pressure is from idle to shut off.

 

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Yes, your downstream O2’s are supposed to “stagnant” as you say ....somewhere around 700-800mv !!...now you said you replaced an IAT pigtail..,did you mean ECT ??...I had asked you to check the ECT after the car sits all night...ECT should be close to outside temp..,did you clear the O2 DTC’s ??...did they come back ???...with key on engine off does your MAP show around 103 KPA ???...mine shows 101...this is based on sea level !!

 

No I replaced the IAT sensor and pigtail, ECT read the outside temperature. Map is currently 98 kPa. So the graph of my O2 sensors looks good? I cleared the O2 DTC’s and they have not returned. The long term fuel trims keep returning to -17. Do I replace the downstream O2 sensors as well? One thing I have failed to tell you is I have a Borla S-type axle-back exhaust. I don’t see that causing these rich fuel trims, would it?

 

As long as the upstreams are switching between 200-800 Mv you are fine...do you have a check engine light ???...I believe at -13 % on your long terms it will set a rich code...if you are reading -17 raise the idle to 2000 rpm or so...do the long terms and short terms go positive ??...towards 0 ??...if it does that is usually a MAF issue !!..try disconnecting the MAF sensor and see if it still stumbles...the engine will default to “speed density” we call it... it’s now relying on MAP, RPM, and TPS for inputs !!...it will throw a code for the MAF when disconnected but you can erase it once it’s reconnected !!...was the TPS angle down around 5% or so at idle ??...I can’t remember !!...I would also reset the fuel trims and see where they go...look at thread #20 !!

 

TPS angle is 5% at idle. MAF sensor removal still caused it to stumble. There was a 2.4 g/s MAF reading when unplugged, no check engine light.

 

Now that I’m thinking about it I bet your EVAP purge valve may be leaking...if it leaks it will draw fuel vapors into the intake from the EVAP canister...what will happen is the engine will run very rich (-17) but then as all those vapors are burned up now your fuel trims will go positive because you basically have a vacuum leak...to check let’s do a “purge and seal”...normally the EVAP vent valve is open...we will close it with the Tech 2 and then watch the fuel pressure sensor voltage...it will read 1.5 volts when open..when we close it the voltage will climb to 2.1 to 2.3 volts or so..if the normally closed purge valve is leaking the fuel pressure sensor will REMAIN at 1.5 volts...go to special functions, output controls, EVAP, and hit enter...scroll down to EVAP vent control (I think it says that) and you will see ON and OFF at the bottom of screen...toggle down to fuel pressure sensor (voltage)... you should see 1.5 volts...now close vent valve by selecting ON...you should see voltage CLIMB...let us know !!...also on startup see what your O2 voltage is...If purge valve leaking O2’s will be very high ...like 800-900Mv and steady !...if so there “should” be some EVAP DTC’s...maybe not...LOL !!

 

How do I find fuel pressure!???! Fuel tank pressure? I cannot find it on the Evap Vent anywhere! Thank you so much for your help!!!

 

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Sorry !!...meant fuel TANK pressure sensor !!...if you look at live data you should see it there !!..1.5 volts !!

 

When I run SD tune you need to get the MAF code or it won’t be in SD mode. You need to get the check engine light on to be SD mode.

 

Ok, i only see it in mmHg, and it goes negative when i vent, i really appreciate your help! Are you sure it’s on this screen?

 

Fuel tank pressure sensor voltage is there somewhere !!...yes, the inches of mercury will decrease when the system is sealed (not venting) and voltage will increase...car must be running !!

 

Ok tommorow I will check after work again, I could not find it.

 

Ok, all GM’s see 1.5 volts...check how much fuel pressure drops after 5 minutes when key on then turned off...also smell the oil and make sure you don’t smell fuel...like was previously mentioned see if those are the right size injectors for your engine

 

Ok, I confirmed they are 26lb injectors. #12456154. I did notice the fuel pressure drop from 52psi to 25psi after about 10 minutes with the key off. This car ran great when I first finished putting it together. I then Took the battery out, cleaned up the wiring harness organization, changed plug wires, and now I am having these issues. It is frustrating let me tell you! I wonder if there is a wiring issue or short somewhere but I need to narrow the system down that I should be investigating. I will check the tank voltage tomorrow afternoon, thanks again for everyone’s help. How do I get the check engine light to come on with the MAF sensor unplugged? The oil does not smell like fuel. I have noticed that the oil gauge is slow to react upon startup..... could this be a ground issue for that sensor?

 

The FSM for my ‘01 says fuel pressure should not drop more than 5 psi after 1 minute !!...check that !!

 

Evap valve? There is no fuel leaking anywhere.

 

No !!...fuel rail pressure !!