5.3 into my 1987 SWB Stepside.

[87OldYeller]

I am needing a little help. I finally got back to working on my truck. I got it running, It will fire up run but will not Idele, as long as you stay in the throttle it will run. Here is the kicker, had no exhaust to speak of just down pipes. Will this engine run with out cats? I have OEM cats that were on it I just don't want to use them unless i have to. There are no emission laws here so no worries about that. I am gonna have full exhaust put on with maybe just some flowmaster 40's

[Venom]

yes these engines will run without exhaust. to me it sounds like a MAF problem or a low fuel pressure problem at idle.

[flattopwill]

yes these engines will run without exhaust. to me it sounds like a MAF problem or a low fuel pressure problem at idle.

Mine wouldnt.

If the O2s are too close to the end of the pipe or getting fresh air in any way the motor will run like shit i.e. not idle.

[Venom]

ive ran motors with open heads in the dealership all the time after engine swaps and stuff. im not say urs didnt flattop just saying ive done it. my suggestion would be to hood the facotory headers up and if it works then buy some high slow maganflow cats or something.

[flattopwill]

Ya and people have told me you cant run these motors without a MAF (not including speed-density tuned setups) but Ive done it.

IF you think it is exhaust related then flash the memory on the pcm and unplug the O2s. This should eliminate that possibility. If it still does it then your problem is elsewhere. Plug in a good scanner to look at your codes, fuel trims, etc.

[classic79]

I know it don't help much but I started mine with only manifolds and no mass air hooked up yet. starts and idles and revs fine, though kinda loud. I don't have any 02 sensors hooked up yet so that should put into a closed loop mode, if you have yours hooked up that might be your issue.

[tlh1230]

Hello everyone. I'm new to any kind of forum. I've done engine swaps b4 but never like this. I have a 1981 silverado LB. I'm doing a 305 to 1998 ls1/4l60e convert.This Is my truck .I think i've pretty much narrowed down the items i need for the switch however, I'm stumped on a few things. What about the gas pedal. Would I need the pedal from the donor vehical? I read that I would have to make a few linkage mods. A little clarity on this would be greatly appreciated. Much thnx for reading...

[87OldYeller]

Been a while since I been here. Done a lot to the truck, got the body put back together, drove it around some. Runs ok I just need some help from the folks here.. The exhaust on the truck is down pipe with 02 sensors and catalytic converters installed but stops there. But truck will Idle great, in neutral if you give it throttle it sounds good but if you get it ½ throttle or much over idle and completely let off the throttle the truck will die but if you come down slow it will idle, put it in drive it will pull off like normal same deal with throttle if you apply enough throttle as to pull off at a decent speed it bogs bad let off it will go back to idle.. sometimes die. Attempt to try burn out it bogs bad and will die. The fuel pump is new the one I used was recommended by other members who have done the swap.

[pl4yboy]

Just for kicks, what's your fuel pressure at the rail when this happens?

[Bigschwerm]

Nice!