04 Sierra keeps dying
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04 Sierra keeps dying Hey guys I’m looking for some info for a problem I’m having with my 04 Sierra. It has 4.8 with cam and head swap FBO. Recently it started acting weird on me. When I’m backing out of the driveway sometimes it starts idling real rough dropping all the way down to around 300-400 rpms then eventually dying. Same thing driving around too. When I come to a stop sign o start slowing down and when I come to a complete stop it starts idling rough and dies sometimes. I’ve read around online and it seems like it may be with fuel pump or maybe the fuel regulator. I’ve changed plugs, wires, I’ve sprayed carb clean all over the intake looking for vacuum leaks but haven’t found anything. It has no check engine light on so I’m kind of lost here. Any info will be appreciated. Thanks I’m advance!
No check engine light is often a fuel delivery issue. Have you checked fuel pressure? Do you have access to tuning software so that maybe you could log when this happens? How is the tune? Truck runs well the rest of the time?
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Checking fuel pressure is going to be my next step. I’ve been looking up what the fuel pressure should show. The truck runs good at WOT it’s just when coasting or coming to a stop it acts up. I’ve asked my tuner about it and he said the tune is fine but it’s never acted up when I’m there. It’s just recently gotten worse this week it’s getting annoying now. Does anyone on here know the exact fuel pressure it should be showing at idle, start up, and part throttle?
Clean the throttle body real good and see what happens.
The throttle body controls idle and as it gets dirty the idle speed lowers and the throttle body has to compensate but it has a max compensation and once it reaches that it won't be able to control idle.
The throttle body controls idle and as it gets dirty the idle speed lowers and the throttle body has to compensate but it has a max compensation and once it reaches that it won't be able to control idle.
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Thread Starter
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I just did a fuel pressure test it had 58 at start up and I put it in reverse held the brake and tapped the gas and it dropped down to 400 then went back to normal. Did it again and it dropped so low it died. No change in fuel pressure. I just recently took the throttle body off and cleaned it good and ported it. It was doing it before I done that and it didn’t make no change. Tomorrow I’m going to take MAF back out clean it again and clean my air filter real good. It’s a little dirty but nothing major. My tune does have a few degrees of timing taken out for my nitrous but I don’t figure that would cause it. I’m starting to get worried because I don’t know what else to do or what it could be.
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Thread Starter
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its a 4.8 with 243 heads milled .035, Cometic .040 head gaskets, 220 .600 lift TSP cam, 7.325 pushrods, FBO, 150 shot of nitrous wet Kit, built 4l60e with PTC 2500-2800 stall. Honestly it didn’t start doing it until I put the bigger cam in it. I had a Howard’s racing .585 lift in it before and it did fine.
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ive has it retuned since then. I even went back again after the retune and he said the tune was good there wasn’t anything wrong with it. I’m thinking about going to another tuner to see what he thinks
The cam obviously isn't the problem, it's a contributor though. But it has to be tuned around that new cam to work right. What is your idle speed? Maybe it needs to be turned up a hair. I'm no tuner though so the complexities of getting one to idle with a cam isn't my wheel house.
its a 4.8 with 243 heads milled .035, Cometic .040 head gaskets, 220 .600 lift TSP cam, 7.325 pushrods, FBO, 150 shot of nitrous wet Kit, built 4l60e with PTC 2500-2800 stall. Honestly it didn’t start doing it until I put the bigger cam in it. I had a Howard’s racing .585 lift in it before and it did fine.
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its drive by wire throttle body. When idling right it idles around 900 rpms right now. I’m going to drive it in the next day or so and upload a video of what it’s doing.
Yeah...tuning. Something like a .5-.75 g/sec idle airflow in the gear section would probably fix your problem. And you should be able to make that idle at 800 no problem. Since its just now getting warmer I imagine you are now getting in to some of the higher ECT's idle airflow numbers, which are typically lower g/sec than the lower ECT numbers.