I just finished putting a :hail: Vortec Headed 350TPI motor with an 86 305 maf setup in my 1968 El Camino. The intake is a SDPC unit, with 24# injectors and I'm using the painless wiring kit (very clean i might add). The heads are the L31 Vortec headed and flow 250 cfm on the int and the exh is up about 20 cfm over stock. The trans is a 700r4 with 1800 stall and the rear gears are 3.73 with a 26 inch tire. The cam in the motor is pretty small, a replacement TPI cam from Comp Cams. The only other mod is a K+N air filter and 3/4 length hedman headers into dual 3 inch 3 chamber flows with tailpipes.
The car runs very well, but I am only getting 12-13 mpg around town or on the freeway. I managed to set a code 44 but I am getting some exhaust grime on my bumper directly above each tailpipe so i figured running rich!
I think my problem might be too big an injector or that the ECM is not calibrated for the mods I have. I ordered up and awaiting the pocket programmer so if anyone has some insight to this it would be much appreciated. The El Co is just my daily driver and hopefully a Tow Vehicle for my boat!
Sorry for the Novel! Thanks all!
:rockon:

 

SS,

You should get very good results with the PROM tuning. You may want to plan on installing a secondary O˛ sensor (probably heated) to verify the O˛ readings your ECM is getting. I'm guessing the ECM is really confused by now.

 

i wish my gas mileage was that good lol. try 7mpg when i'm NOT getting on it lmao

 

99 out of 100 times if you are getting a lean code, but you know thw car is running rich you have a bad O2 sensor, or the circuit is otherwise corrupted. It's as simple as that, the ECM is seeing a lean condition and is adding extra fuel, and it still sees lean, so it adds more fuel, until it is maxing the BLM at which point it sets the code.

You can verify this very easily with a digital voltmeter. The digital part is important as an analog voltmeter draws significantly more current and kills ths sensor. As will ever allowing the O2 sensor to ground, EVEN with the car off, if the exhaust is still hot the sensor is active and will kill itself. Thats why a compromised circuit is also likely since it only has to touch for a second or 2. Another possibility that has happened to me personally is the sensor just intermittently failed to send a signal, it would just turn off for a few seconds. This never gave me a 13, but would give me 44s and gas mileage was in the toilet.

I reckon a bad MAF could do similar things, but i'd still lean towards the O2 if for the black bumpers alone.

 

Ed,

What kind of cam are you using?

 

stock

 

Well I am off to the parts store to get an O2 sensor, it probably cant hurt to change it anyways, . I am running the standard 1 wire O2.
Ed Maher, you said the BLM values might be maxed out , I do have a X-RAY scan tool and It shows the BLM values at 128, I swear I thought it was a default because I have never seen anything other than 128 on it, even in the real time monitor mode!
Does it have an operating range or does it just continue to add to allow for corrections to the fuel? Is their an "ideal" value it should be at?
Thanks for all the help Guys, I am a TPI Newbie and reading this forum has helped out soo much. The prom burning is still overwhelming for me........ has anyones head exploded yet?

 

OK, if you have a scan tool then you are way ahead of the game here. Depending on the tool you have you should be able to check the flag to see if you are getting into closed loop. If your O2 is shot, that could keeo you from going into closed loop, ans thus your BLMs stay where they are.

Here's a post i made not too long ago explaining how BLMs work:
https://www.thirdgen.org/techbb2/sho...&highlight=BLM

If you're not seeing our BLM change it would appear that you aren't even getting closed loop. When in open loop, the ECM doesn't try to compensate for fuel, it just goes right off the tables in the ECM. With your 24lb injectors and a stock chip the values in the tables your ECM is using are all way too high, thus why you are overrich.

If you get a working O2 sensor in there, and you can see that teh coolant temp sensor is reporting the right coolant temp to the ECM you should definitely get into closed loop. Then you'll be able to see how far off you really are. As i already said, right now you are running way too rich with a stock chip and those injectors. It's even possible that you are so grossly rich that you are fouling the O2 sensor and keeping it from reporting properly.

Don't be intimidated by PROM burning. Especially since you are running a small cam and MAF you don't even have to do any of the hard work of tuning the MAF tables really. Check the sticky at the top of the TPI board for explanations on changing the basic stuff in the PROM that you'll need to tweak, if you can handle a web browser you can handle simple PROM changes

 

Thanks for the link to the post, I checked out the blm and it is staying at 128 and the car is going in closed loop mode as soon as it warms up. It stays in closed loop but i am still going to try the injector prom changes. Have you had any luck with the ARAP BIN? I was considering trying it with the injector constrant changed as soon as my pocket programmer comes in the mail ! Hurry FEDEX!!!