Hi,

Here's the scenario, I have an 87 coupe and just installed 1 3/4" EM long tube headers on a stock engine. Yes, I realize that 1 5/8" would be better, but I am going with major upgrades later that will require 1 3/4 tubes.

So, my question is, how bad should this stock engine run with 1 3/4" headers and no exhaust?

I realize that the computer and its controls have leeway, but. would they adjust enough to make an L98 run decent with 1 3/4" headers and no exhaust?

Right now, the car is running kinda crappy with back fire thru the exhaust.

No codes are being thrown.

Yes, I will be putting a Corsa system on it soon, just got it running again and am wondering if the bad running of the engine is simply due to a lack of exhaust back pressure.

Your thoughts would be greatly appreciated!! :)

 

Oh, btw, because the O2 sensor is relocated to the header collector. I did switch to a Bosch 3 wire heated O2 sensor :smash:

 

With the heated O2 sensor your computer should be able to compensate and run perfectly at part throttle with the headers, it will adjust the A/F ratio accordingly. At WOT you'll probably be a little bit lean because of the added airflow from the headers, but still safe.

If your engine is running like crap it is probably because of the open headers. In between exhaust pulses air can flow back into the collector and make the O2 sensor readings incorrect, causing the car to do all kinds of stupid things. If it's gonna be a while before you can finish your exhaust system you might try just fabricating some pipes to bolt onto the collector, just to extend the end of the pipe past the O2 sensor. A foot or two of pipe past the O2 would make a ton of difference in how the car runs. :cheers:

 

Thanks for your reply Nathan

Today, I did put on the EM header extensions (which terminate at the rear of the transmission) and it made no difference.

Still no codes being thrown, backfiring, running rough and the throttle response is pretty horrible really.

Instead of being lean like we would expect, its running on the rich side, specially when I blip the throttle. The fuel pressure is about 46-48 with the vacuum line disconnected and about an even 40 with the vacuum line connected.

Damn, wish this thing would throw a code so I could have something to check out!

Any other idea's??

 

Bump

I did change the plugs/cap/rotor/wires and still it runs like crap and posts no trouble codes

Anyone with idea's??

 

Hmmm. Sounds like the sensor is still staying too cold. When I realized that I had to convert to heated sensors it was running so rich that it would make your eyes water. The driveability was absolutely terrible too until the sensor would heat up.

Try this. Fire the car up cold and see how it runs in open loop, should to pretty well. If at all possible try to drive it for several miles at a good speed, around 55 if you can. When you first stop from your "run" the car should idle pretty well. Then as the O2 sensor cools off it should run progressively worse. If this is the case I'd say you either still don't have enough pipe, or your heater on the sensor isn't working right.
:cheers:

 

Thanks again for your reply Nathan, I was hoping that others would chime in as well with thoughts. Specially from those tons of folks here on the CF forums who have installed headers and fired them up without exhausts (for the fun of it of course!) But I guess this is something that the people here don't want to talk about.

Kinda a shame really cause I would have thought many folks would have been interested in how other cars ran with open exhaust.

Now the good news, I couldn't get the puter to throw codes even though it ran like crap and was rich. So I took a chance and put in a new ECM. Holy crap, what a difference!! This was very hard for me to do because I know that the vast majority of ECM's (on all cars) that get replaced are not faulty at all. So I gave it a shot despite the odds that it was bad and it helped significantly!

Is the car running perfect now? Nah, about 90% I would say. Who knows, maybe the last 10% would be due to the lack of backpressure.

Nonetheless, I will get the exhaust on and let ya know the difference it makes for both, the good or the bad.

Thanks again and I will let ya know the latest tomorrow!

 

Bump

Well, been kinda slow spending time on the car lately, but making progress (I think)

Still, it would be great to hear other forum members results when they ran an open exhaust on an otherwises stock engine! Surely I can't be the first one on these forums to try this!!

So tell us, what were your results in the same scenario?

 

When I installed my TPIS 1 3/4" longtubes I ran them open headers for a couple miles just to try it out. Ran just fine, but I upped the fuel pressure a little and installed a 3-wire sensor. Idle was a little funky until the engine warmed up good but other then that it was perfect, just deafening!

 

I never ran mine for very long with the headers open so I can't contribute much to that end of the discussion. I don't recall my engine running much differently than before the install; just louder, without any mufflers bolted up.

I did discover that my system would drop out of closed loop at idle, but even that wasn't noticable. I only found out it was doing it by running Diacom with the engine idling. A heated 02 solved that.

One the main things about these computer-controlled engines (when they begin to act as yours is) is that in order to really see what's going on, you need to get real-time data.

That calls for Diacom, a ScanTool, AutoXRay, etc., so you can see the numbers. Without that info, you're pretty much shooting in the dark. The cause could be one thing, or a combination of things.

02 cross counts and closed loop status could tell you if the open headers, alone, are causing the problem. Other factors, like injector pulse timing, airflow, coolant temp readings, BLM and Integrator values, etc., are other things that air important to know after modifying an engine and beginning the tuning process.

The shops that re-burn PROMS have a baseline program for many of the most popular combos guys run, but even those often need tweaking because of the subtle differences among engines.

Just changing parts in the hope of hitting on the right one isn't the way I'd recommend attacking the problem. You'll very well end up changing a part that didn't need changing and that's $ down the drain. Besides, the cost of the computer program will pay for itself in short order; well worth the investment.

Since you wanted more input, these are my thoughts.

Jake