Ok, here's the deal. I have an LT4 hot cam in my 305 TPI. I have world products 58cc heads, headers, edelbrock intake, slp runners, Accel 19# injectors, msd 6al, and holley afpr. The prom is from TPIS (programmed for basically just the eshaust). I realize i need to get tuned, but my question is, why am i running very rich with this setup? All the sensors seem to be working properly (did volt and ohm tests on them). I don't have a good scanner, but i have a code scanner, and it reads "open loop". I've replaced the O2 sensor, the sparkplugs, made sure sensors were giving a signal to the ecm, and even got a new ecm. The fuel pressure is set at 47 psi, and TPS is set within correct voltage range with throttle closed (.6v). one of the strangest things is, for the car to idle, the timing is advanced a whole lot (not sure how much exactly, but its a good amount). It won't idle at base timing. I put .032" thick 350 head gaskets on it (suppose to with these WP heads). It seems like its having a compression problem, but the compression was fine before the head swap. I'm almost certain i degreed the cam right, although i might do it again to make sure. I'm also gonna make sure the valves aren't over lashed. If any body has any suggestions, ideas, opinions, etc., PLEASE, throw em at me. I'm stumped, and my brain is really starting to hurt.

 

TPort,

Running rich? If you still have the original EPROM/CALPAK, you might want to install that just to see if the problems persist. It's possible (but not likely) that teh custom programming for your ECM has base fuel tables that are way rich, or there was some other error in teh programming.

The fact that you cannont achieve closed loop is another concern, and may involve the EPROM as well. Are there any error codes generated?

Even the stock EPROM will run rich (about 12:1) until the ECM is in closed loop mode. You really only need to have a couple of things to achieve closed loop:

• CTS >40.7°C (105°F) for 12.5 seconds;;
  
• O2 >0.699V & O2<1.99V for 10 seconds;;

If you believe the oxygen sensor is operating and producing a signal (your scanner should be able to tell you that) you might want to check the CTS input. Again, the scanner should produce soem data on that. If the O² sensor is not hot enough, it will not produce a good signal long enough to satisfy the check timer. Sitting at idle may not be enough to keep the sensor hot, especially with headers that tend to shed exhaust gas heat faster than cast manifolds.

 

If you have a MAF sensor, take a close look at that. If it isn't functioning properly your car will run super rich. I just had this problem. The MAF read O.K. on the scanner. I found the problem when the MAF was reading 15g/s with the engine off. I guess it wasn't calibrated correctly. If you don't have a MAF then I would suspect the programming. An LT4 hot cam car will never run that great with near-stock programming(especially with a MAP sensor)

 

Well, i'm almost certain that i'm getting at least a signal to my O2 sensor, because its hooked up to an A/F ratio gauge. when the engine is cold, it doesn't give a true signal, obviously because its heated up. Once heated up, the gauge starts reading rich. I'm pretty sure the CTS sensor works. I tested to see if its recieving the 5 v signal (well, 4.98v), and it reads in the mid 8000 ohm range for resistance (its pretty cold in the garage), so the resistance part seems to be ok.

When i tested the MAP sensor, i tested it when the ignition was in the run position, but not when the engine was running. I was getting the 5v input (4.98v) and a 5v reference (once again, 4.98v), so it was basically reading no vacuum, which it should with the engine not running. I do have another MAP sensor from my TBI (I kind of keep everything around, almost like a parts store.... nothing for sell yet... ), so i'll give that a try, just in case i do have a faulty MAP some how.

Oh, i did notice something else. At one point, the A/F gauge was "bouncing" between rich and lean at one point, as if it was changing its voltage from lean to rich to lean, etc. But i'm not sure if its suppose to work that way. I didn't check to see if i'm getting a signal from the MAT sensor, although i don't think that should matter too much. Anyway, the gauge just went to rich again, and stayed. It did go down a little when i retarded the timing back closer to 0*, but like i said, my car just up and dies at 0* base timing.

I don't have one of those good scanners that have a readable screen. I've just been going by a code scanner, a digital volt meter, and a shop manual. Kind of like sorting through 100,000 things one at a time.

Any more thoughts would be very much appreciated. Oh, its a speed density system by the way if any one wasn't sure.

 

Oh, and does anyone have any ideas as to why i have to have a very advanced timing? I'm not sure how advanced it is, i think its around 10* advanced or something like that. it was at 0 before the heads. any ideas?