Here's my situation 86 or 87 305 motor with 113 aluminum heads, speed density tpi. New injectors, fresh overhaul on motor (1200 mi.). Frame rail mounted fuel pump from Summit with a flow rating of 43gph @ 40psi. Fuel pressure engine off, pump on +- 38psi at the fuel rail. Engine on at idle, +- 36psi.

Problem1---Long crank time when cold (over night temps 70-50 deg.). +- 15 sec. crank times.

Problem2---Engine seems to lean out at about 3000 rpm. Serious miss, backfiring etc.

Once the engine warms up it starts, idles and drives fine at rpms below 3000.

Could the IAC valve be causing any of these problems? Other ideas?

I'm not knowledgeable at all about these TPI systems.

Bud

 

Do you still have the pump in the tank? That inline pump seems a little small; I believe the stock pump flows about 50% more than that one.

 

I had that problem with 19lb injectors. switched to 21lbs, problem solved.

 

Has the ecm been tuned for those mods?

 

Thanks for the replies. No pump in the tank, inline only. The injectors are new ones recommended by the local fuel injection specialty shop. The ECM was moded for this setup by the same shop. I just found a small vacuum leak at the MAP sensor. Fixed that and it seems to have improved the long crank time issue but I won't know for sure until I let it sit over night and try a cold start. Could that vacuum leak cause the leaning out symtoms (misfiring and backfiring) in the +3000 rpm range? I didn't do a road test after fixing the vac leak, too much traffic this time of day.

Thanks
Bud

 

out of curiostiy, do you know the flow rate of the injectors?? Which ones are they?
Do you have a part number? I can try to crossreference it for you to make sure they are the appropriate flow rate for your application

 

Southbay
Unfortunately, I couldn't find the invoice fot the injectors but according to the invoice I got for a piggy back chip the injectors are 19pph Accels.
Bud

 

If it was tuned right then it sounds fuel related. Long crank time, does it smell like fuel? Or does it seem way lean and it takes long cranks to fill with fuel before it fires?

Definately check for vacuum leaks and timing. Make sure its not off. Est connected, etc. then maybe try adjusting fuel pressure to see what it wants. Do spark plugs look like they are lean?

 

Long crank time when it sits overnight or longer. Fires within 5 revolutions after it has been run for a couple of minutes. If it was a carburated motor I would assume the fuel bowl was draining down overnight but I get pressure to the rails as soon as I turn the key on, maybe 20psi first, then 38 or so if I cycle the pump. Plugs look good, not black, just a light gray, if any, coating. Seems to be in good tune at lower rpms(2000 & below). Will occasionally backfire through the intake if i start it cold and drive off immediately. Per specs, timing set at 5 deg.BTC at idle. HEI dist., new accel plugs, Taylor plug wires. 16" vacuum@ idle. So far the only thing I have discovered is a small vaccum leak where the hose connects to the MAP sensor, enough so that I could here a change in the idle when I wiggled the hose. Fixed that and will check cold start performance and upper rpm performance on the way to the injection shop tomorrow morning. I'll let you know.

Thanks
Bud

 

I feel better now. When I cranked the car this morning it lit off after only about 5 secs. of cranking and idled smoothly. I'll test the upper rpm range later today. If I still have the miss and backfire. The injection shop wants to put the car on their dyno. Little reluctant to do that cause I've never had a car on a dyno before and I don't want to break something. Of course if it is going to break I guess its better to break on a dyno in the shop than halfway between timbuktu and bumf--- Egypt on the freeway.

Bud