I have a completely rebuilt pre-86 355 small block using a MAF TPI setup from an 87' camaro installed in a 79 el camino. The entire TPI setup being used is completly stock, with all components working properly. Currently no 02 sensor is being utilized. Motor has not ran, although will fire.


The problem we are having is that the motor will not combust with the throtte body in closed position, but if the throttle is held open all cylinders will combust. I have not been able to find any evidence to what may be the problem. All sensors function properly and are correctly adjusted. Except for the o2 sensor, although i can not find any evidence as to why this would not allow the motor to start. Please leave any suggestions you may think of, also let me know if i can provide anymore info that will help you to analyze this problem.

thanks,
brandon

 

Well...could be alot of things. You only need three things for a motor to run....fuel, spark and compression. When you say "combust" does that mean it sputters and trys to run or do you just get a random cough as your cranking it?
Have you checked to see if the injectors are pulsing yet? I assume you have a good high pressure pump installed. Do you have a pressure regulator on it? What's the pressure set at? How about timing.....what do you have this set at?

 

Yes all cyclinders will sputter at and trys to run. Yes injectors pulsate, this was check by a gm tpi noid light, also all injectors have just been flowed and matched by cruzinperformance. Correct again our fuel pressure holds at 47 PSI. The fuel pressure regulator is stock and non-adjustable. the timing is currenlty set at 6* BTDC. We have turning the dist. in small increments both to advance and retard spark, with throttle closed no noticable difference. Like i said it will only sputter when the throttle is held open

 

Hmmm....do you have any means to plug in a scanner or datalogger to see that all the sensors are reading okay?
I assume you double checked the firing order and that your dist. in not 180 off?
Have you pulled any plugs yet to see if they are wet with gas? Can you spray starting fluid into the TB and will it run?

 

Yes all timing is correct. I have a laptop but do not have the software nor connector to us with it. What have you found to be the best software and connector combination? With the throttle held open the motor just sputter like it is trying to start, even with a shot or two of starter fluid.

 

Interesting, sounds like it's getting fuel then. Timing is okay too. I'm wondering if it's getting too much fuel? A quick test you could do is disable the fuel pump and see if you can make it run off starting fluid. I had that happen to me a few years ago...trying to start a fresh motor and it just wouldn't fire up. Turned out I had a bad coolant sensor and it was makng the ecm dump in WAY too much fuel.......you might try that.

As far as datalogging goes....I use Diacom only because a good friend of mine lets me use his

 

Did you get it figured out yet?

 

Yes actually we did get it figure out. A couple of the valves were not fully closing. So we just backed those valves off another turn and it fired right up. I appreciate all your help and thanks a lot.


Brandon

 

Cool