I just bought a car ( 95 TA ) and the thing runs awful rich at idle....I mean you can smell it in the drivers seat.

The car was built and tuned by Morgan Motorsports in Reseda CA, to the tune of 387 rwhp. It runs awesome but man....I don't see the need for the car to run so rich at idle.

The car has had 30k miles put on it since the complete install and tuning of the LT4. The guy gave me all the receipts for the work done to it. The car just turned over the 100k mile mark when I drove it home.

Nowhere in the receipts did I ever see that the O2 sensor was ever changed. Could this be why it is now running rich? The car never has even the clue of a Check Engine light....but I'm sure it's because of the DFI.

What do you guys think? I was thinking it would be a good thing to do anyway, regardless of if it would benefit the rich mixture. BTW- I do not know the details on the Accel DFI but it was installed in the year 2000 if that helps and it's a piggy back system to the stock ECM.

 

I would hook up my lap top and see what the air/fuel ratio is at idle. If it toggles to the right of 14.7:1 then DFI is dumping more fuel into the motor causing a rich condition. It could be a faulty O2 sensor but I would check for a exhaust leak as well. Even the smallest exhaust leak will tell DFI to add fuel.

The laptop would be the best start to see what is going on. If you do have a exhaust leak it would most likely show up while you are driving as the air/fuel ratio will be all over the place. I hope you got the harness to hook up your laptop. You can download the software from Accel's website.

 

There are exhaust leaks. Header leaks to be exact. I can hear them ticking when I pop the hood.

I do not have a harness or anything like that. I just bought the car....done....well pretty much done. It was built by Morgan Motorsports in Reseda CA. They did all the dyno tuning and tweaking of the DFI.

The car is getting terrible mileage....much worse than it should. My carbed car did way better, I know I am dealing with a whole different animal here but I even had my carb running rich just to be on the safe side.

I did not know OBD1 cars had 2 Oxygen sensors???? I priced them out at AutoZone for 52 bucks apiece.

Do you think the header leaks are more likely to be the culprit???

I would assume that any leaks behind the cat would be irrelevant. The cat is also hollowed out. Would that make the car run richer or leaner???

I will contact Accel for the harness to hook up to my Laptop.

 

I uhhh......checked those "header leaks" today. I tightened all the bolts...started her up and VIOLA!!!

Sounds
exactly the same. I put my hand all over the place, even underneath trying to feel for are and....they are sealed up pretty tight.

Wanna know what the ticking is??? My valvetrain! There is a $300 set of 1.6 rockers on this motor that haven't been adjusted for 30k miles.

Man this thing needs a tune.

So I bought a manual today and saw that there is an O2 sensor in each header. So the only exhaust leaks that would play a major part would be those from the Y-pipe and forward right? She is sealed up pretty good anyways.

So here's what I figure. I'm gonna take the car back to Morgan Motorsports soon, have them hook up the laptop and tell me what is going on.

I am sure that the rockers need adjustment, but that is aside from the car running so rich. I think the 02 sensors need replacing since they have 100k on them but I wanted to run it by you guys 1st.

THE ACCEL DFI IS STILL A SELF ADJUSTING UNIT RIGHT???AS IN IT STILL CALIBRATES THE A/F RATIO LIKE A STOCK ECM, RIGHT???

If I am way off, please explain this DFI thing to me.

 

Sound like the headers are tight but the gasket could be damaged. You are right in the aspect that any leak more than 24 inches behind the O2 sensors will not affect them but any leak from that point to the front of them will.

It would be a good idea to run the car back by MMS and have them check it out. Be sure and watch as it will be to your advantage to learn how to diagnose problems that may occure.

Yes, DFI is in control of the engine management functions. With the piggy back the OEM ECM controls all other function like ABS, A/C clutch engagement, ect. and gives DFI all engine management functions.

 

Get this.

I just got off the phone with MMS and the guys tells me that they don't even tune DFI anymore.

He argued with me when I told him that the roller rockers needed adjustment because I could hear them ticking. I said, well, give me another reason why I hear ticking under the valve cover. He replies: Oh, well I guees it could be just normal wear, maybe they are a little looser than they were 30k miles ago when we did the work.

So they don't even have the harnesses anymore, cause they just do LS1's now. Go figure, Damn LS1. The guy seemed to think that even if I did have the harness, you can't retrieve diagnostic codes off of a DFI system. He's joking right? I was like oh, so it's kind of a hit and miss then huh? I should just start replacing sensors?

Well, he did say that my 02 sensor theory could very well be the culprit. 100k mile sensors are old, really old. Rich enough to smell in the front seat though....damn. They must have so much crap and soot on them.....maybe they are just plain fouled???

Any ideas on what I should do????

 

He is right, DFI does not have diag. codes like the OEM ECM. It is pretty simple to figue out though if you can hook a laptop to the DFI. The piggy back takes engine management from the OEM ECM and gives it to DFI so codes for engine sensors will not trip the check engine light. By monitoring the Base Fuel Map in Calmap there is a air/fuel ratio gauge that is active when in closed loop. If the guage is greater than 14.7:1 A/F ratio then DFI is adding fuel to the Base Map which will cause a rich condition. If the Base Map was programed properly then it should not need adjustment. That puts you back to the inputs and outputs that would cause a rich condition.
1. exhaust leak
2. O2 sensors bad
3. 1 or more fuel injectors are leaking
If you want to try to get a harness call Mac at Fasttrack Performance. Link below.
http://www.fasttrackperformance.com/
He is in Ferndale, Ca. Don't know how far that is from you but it may be worth a road trip.

 

You have an option that doesn't include playing with the DFI. You can just get rid of it altogether and run the factory ecm. The factory ecm can be programmed nowadays but maybe it wasn't available at the time this car was built. There are more than a few guys with 400 rwhp still using the factory ecm on LT1 cars. There is a list for LT1-edit or something like that which you could research. The best software, just personal opinion, is from tunercat and with their software ($100) and a cable ($35-75) you could be programming the factory ecm. The same cable with a free diagnostic software called Freescan and a laptop and you can see what the ecm is "seeing".

 

I changed out the 02 sensors, I am getting 2.5-3 mpg more on the highway. There are definately exhaust leaks, the first time I searched around for air with my had, the motor was hot and I didn't want to burn myself. I already bought some Ultraseal header gaskets for it, I'll put them on next week.

 

I am glad to hear things are going in the right direction!