What would cause the car to run better in open loop than in closed? When my car goes into closed loop it's impossible to get it off the line and is down on power until about 3000rpm.

87 LB9 auto, and it isn't throwing any codes.

Any ideas?

 

The computer doesn't pay attention to the O2 sensor until it goes into closed loop.

Sounds like you have a situation where there's too much fuel being wasted into the exhaust. In open loop, it probably won't show up with performance problems. But in closed loop, the ECM will react to it, pull out fuel until it gets the exhaust mixture back to ~14.7:1. In that case, whichever side of the engine your O2 sensor is located is likely to be where the problem is located as well.

Does it feel like you have a misfire anywhere? Perhaps a bad plug, plug wire, injector, etc? If this is the case, the computer will remove fuel from the distribution to the entire engine in order to compensate for one bad cylinder. So all of the remaining cylinders will end up leaner than necessary- which may result in the problem you're experiencing.

 

I have a 91 with the L98 and your problem sounds identical to the problem I am experiencing. I replaced my plug wires hoping that would fix it since I had a couple of wires that looked bad, but no luck yet.

 

Did you actually test the wires before replacing them, or just replace them because they looked bad? With a problem like this, you need to actually test things, otherwise you'll be throwing money at it for a while... Could be a bad injector not firing enough fuel, or leaking to much fuel, a bad plug/cap/rotor/etc. Lots of things need to be checked out.

Personally, I would check the resistance of the injectors, then test them for leak down... Then check the ignition module, cap, rotor, then go for things like gas line filter and monitor fuel pressure to see if it's dropping... Have a plan and check things out systematically...

 

One of my wires was somehow corroding inside the boot and another one had been ripped at one point and we ended up putting electrical tape on it for a temporary fix. The plugs/cap/rotor are all a month old.

I got a new Delco O2 sensor today and am going to replace it tomorrow...it has been in since january and the car seems to have been running a little more on the fat side than i would like. If the O2 doesn't fix it then, I am going to check the resistance of the injectors. I am about 75-80% sure that the O2 will fix the problem though as it only seems to be acting like it is misfiring at part throttle in closed loop. when i go WOT in closed loop there is no miss at all, which leads me to believe that the O2 is faulty. I am also not ruling out a possible ignition control module since i have been seeing a code 42 recently...almost on a daily basis.

Any other ideas that you may have are welcome...thanks for the help thus far and i hope all of this is helping RMK out as well.

 

bnoon...i just checked the resistance of my injectors and i think i have found my culprit.

Here is what I found:
#1 - 18.0
#2 - 17.3
#3 - 17.9
#4 - 17.5
#5 - 18.5
#6 - 17.4
#7 - 0.66
#8 - 17.5

From the looks of it, I think the #7 injector has decided to retire...what do you guys think

 

Yep, number 7 is the problem. Allen

 

This is some of the best advice I've read. I continually try to get this point across on the CorvetteForum: Check/diagnose first, then buy parts if necessary.

Jake

 

If you can't find a replacement, I have a set I removed from my 1986, 350 Vette engine when I installed the bigger engine. If you need one, let me know; jakejr266@sbcglobal.net

Jake

 

thanks for the offer Jake, but I have decided to go with a bigger injector and afpr. i will be needing the bigger injectors more than likely in the future anyways, so i figured i would just get them now and not have to worry about it later unless something else goes wrong with them.

 

sorry I haven't got back to this post sooner but I've been busy with work and the car.

I checked the resistance of my injectors and I found the following


1. 16.3
2. 16.3
3. 16.4
4. 16.3
5. 16.3
6. 16.2
7. 16.2
8. 16.3

So it seems my injectors are ok. I also did a leak down test about 2 weeks ago abd they look good there too. I lost about 10psi in about 20 minutes.

What sensors are used in open loop? I'm wondering if my problem could be the O2 sensor?

Thanks again.

Robert

 

In open loop the ECM ignores 02 input and runs off tables programmed in the PROM using input from the MAF and coolant temp sensor.

If the TPS is faulty and sets code 21 or 22, the ECM does the same thing. It that case it's in Limp Home mode where ignition timing is also curtailed and the engines runs off the initial timing advance and a small amount in the module.

This probably applies to all MAF L98s, but I'm not sure how SD systems are handled.

Jake