Problem with surging idle and engine dying

[JoshH]

Hey guys. I'm about to pull my hair out trying to get this gasser tuning figured out. I am working on an 06 Silverado with a Magna Charged 4.8L V8 with a 5 speed, long tube headers, and I think a cam. I have no idea what cam is in the engine. I am also not 100% certain what size injectors are in it. I emailed Magna Charger, and the guy there told me they should be 43 lbs/hr at 58 psi.

Anyway, I installed a WBO2 sensor to try to get the tuning dialed in. I followed some of the VE table tuning tutorials and idle tuning threads on here, but the truck still has problems randomly dropping RPM at idle and either surging back up or dying. It happens worse in low speed maneuvers with the clutch disengaged while turning (such as into a driveway or parking spot), but it will also do it just pulling up to a stop sign or red light. It also gets terrible gas mileage. Typically around 13 MPG.

Can someone please tell me what PIDs to log and what areas of the tune I should look at? I'm out of ideas here.

[Mr. P.]

First idea is, don't assume!! I helped a friend this winter with a TVS-1900 kit which we were ASSURED came with 60# injectors, and they turned out to be marine 43# units; tuning was a biatch until DOH! we were told by our tuner to actually take a picture of the part number on the injector and send it to him for identification! Total rookie-move on our part. So my point is, pull an injector and get the part number off of it (you may be able to read one of the injectors without pulling it). Also, did they install the Walbro fuel pump in-tank as well?? Just make sure of what you are tuning! Are you running the stock throttle body, or did they upgrade to 90mm? Are you running the MAF, and what CAI is being used? Are you using COS3?

The "randomly dropping RPM" that you describe is the engine actually dying and bouncing off the "stall saver" IMO.

Since you have been following the tutorials, I assume you have some logs - post one or two of them along with your current tune for review and some pointers.

Mr. P.

[L31Sleeper]

I don't think any of the "LS" engines run 58 PSI fuel pressure, unless the kit comes with an
aftermarket Fuel Pressure Regulator.

-Justin

[minytrker]

I don't think any of the "LS" engines run 58 PSI fuel pressure, unless the kit comes with an
aftermarket Fuel Pressure Regulator.

-Justin

Im confused....LS motors run 58psi from the factory.

[minytrker]

I agree with Mr.P 100% don't assume anything when dealing with these "kits" I run into it all the time people not having the parts they thought they did. I also went through something similar with a pro charger car.

[Mr. P.]

I don't think any of the "LS" engines run 58 PSI fuel pressure, unless the kit comes with an
aftermarket Fuel Pressure Regulator.

-Justin

Well, 58-psi when the key is on and the engine not running (zero manifold vacuum). On my own truck with factory full-return fuel system, the regulator will vary the fuel pressure from 48 to 65 psi at the rail depending on vacuum reading in the manifold; on factory returnless systems where the regulator/filter is in-tank, they are 58-psi at startup and will fall as demand begins to exceed pump capacity.

Mr. P.

p.s. another thing I have seen, when you have the key on but the engine not running - the PCM will energize the fuel pump for a few seconds and then shut the pump off while the engine is not running, you will see the PSI drop until you start the motor and the PCM turns the pump relay on again!

[joecar]

With the manifold referenced FPR, temporarily remove the air hose and measure the rail pressure (with engine running)...

you'll find it to be 58 psi.

[JoshH]

I'm trying not to assume anything. I have been working off of the info I was given, but I do question its accuracy. I'll see if I can get a good look at an injector or pull one out to get the info off of it. I do not know for sure if the upgraded pump was installed with the charger. The truck does have an Auto Meter fuel pressure gauge installed. It reads right at 50 psi almost all the time unless you really get on it; it will drop a few lbs to maybe 47 psi. I used the info from Magnuson and the readings I was getting from the gauge installed in the truck and plugged that into the injector flow spreadsheet to create the injector flow table.

The throttle body is stock as far as I can tell. MAF is still being used. No custom OS as this is an 06 truck, and last I checked, there weren't any COSs for them. I'll look through what I have as far as logs go and see if I can find some that show the problem.

Do you guys think the low fuel pressure could be part of the problem? It never gets above 50 psi (even with the engine off). I also verified the Auto Meter gauge with a mechanical gauge.

[JoshH]

Here are a few logs and the current tune. The logs do not necessarily go with the tune I have attached, but it still does the same thing.

[JoshH]

Anybody? Anyone know of someone in the Dallas area that can dyno tune the truck and get the idle straightened out? I think this one is beyond my abilities.