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.

[minytrker]

Im in College Station...thats not that far away.

[slows10]

Look at table B4603. It might help with your idle problems. Are they supposed to be all 0 in the two right hand columns? Also you need to find what the injector size is. 47 psi under load seems low. You also have some out of range values.

[Mr. P.]

OK some more tidbits that might help here -

50-psi is recipie for disaster; minimum fuel rail psi is 55psi, even under WOT demand. Gotta find and fix that. We've installed literally a dozen Radix kits on GM trucks in "the carport" so we've got lots of mechanical experience with the product so we can help there. Tuning experience, we always farm that work out to an actual professional because we have day jobs and do not want the liability of having to support the customer post-tune, and I am still learning to tune myself so I can only help you so far in that regard.

Before you tune, you have got to make sure the 'hardware' is right - if I were me in your shoes I would drop the fuel tank and make sure the Walbro is in there, if not you can get the Radix fuel pump module upgrade kit complete from Magnusson for $135 bones IMO not a bad deal (comes with pump, sock, fittings, etc complete). If the Walbro *is* in there, then I would consider replacing the in-tank fuel filter/regulator, problem is that those are not available even from GM so you have to get one from a low-low-low mile junkyard truck or buy a whole new "fuel pump assembly" from the dealer ($300-400). With fuel pressures you describe (waaaay low) it will force you to fudge false IFR and VE table values to get the truck to even drive, and worst thing is that with fuel delivery that low you'll burn up the motor. So address that first. Totally sucks, I know.

Mr. P.

BTW I'm located near Stonebriar (Frisco).

[Mr. P.]

Found a link for the injector part numbers you PM'd me about - http://www.racetronix.com/17113739.html - they are 44-pounders. The IFR table in the tune you posted is very close to what we use (the values in our table are about 5% 'fatter'), but the fuel rail pressure may be low enough to throw the fueling off.

Mr. P. :)

[JoshH]

I'm bringing this back up. After a short break, I'm working on this again. I have been logging and using the Calc.VET tutorial to calibrate the VE table and MAF calibration. While calibrating the MAF sensor, I found an anomaly. I'm posting a screen shot of the table. I'm thinking this may have something to do with the idle problem I have been fighting. What should I be looking for as the cause of this issue? Faulty MAF sensor?

[minytrker]

Tha MAF curve doesnt look good.....you want it be nice and smooth. You should defiantly feel a stumble or something when you hit that part of the tune.

[The Alchemist]

need a hand..... PM your email can get the thing idling for you at least...without stalling (its the hardest part! ) tuning fuel and spark is up to you mate

[HartRod]

Does anyone have a good sloped IFR data for these injectors? TIA