Hey guys,

I have a Procharger P1SC on my 2001 Denali. I know its a LQ4, not and LS1, but I figured you guys would have better knowledge on a Procharger system as most trucks out there aren't supercharged.

I bought my truck used and it had the system already installed. It has an FMU mounted to the firewall that looks identical to this one:



I also have an Autometer mechanical boost gauge, and electrical fuel pressure gauge mounted on the A-pillar.

Lately my truck has been feeling sluggish under boost. My fuel pressure used to be about 37-40 psi @ idle-in gear, and as much as 100psi when pushing 9psi. Now my fuel pressure is a constant 42 psi @ idle, and under boost is climbs to about 45psi, thats it. My truck hasn't set any codes for lean conditions, but its got me worried because I know that something isn't right.

The system uses a secondary inline pump. I disconnected the secondary pump and the stock pump one at a time, and the truck will still start and run on either pump, so I know both pumps are good.

I used the outlet fitting on my handheld Mityvac vacuum pump, to simulate boost to the FMU hose. Key on, engine off, the gauge showed about 80psi of fuel pressure. This shows me that the FMU is capable of making high fuel pressure when the truck is off, but not when its running. I also replaced the vacuum hose going from the intake to the FMU. I just discovered that the little plastic coupling that was inline in that hose is acutally an orifice to reduce flow to the FMU. I thought it was just a coupling because someone wanted to join two pieces of hose together when they put the hose one, so I threw it away and replaced it with one piece. I'll have to go back and fix that , but it is not the source of my problem.

My next step is I'm going to replace the fuel filter tomorrow. Its 1 year old and has about 15,000 miles on it. I figured it would be a good thing to rule out. I'm also going to try hooking up my Matco fuel pressure gauge to the rail, just to verify that my Autometer gauge is reading correctly. I'm pretty sure this isn't the problem, because the truck doesn't have the same power under boost as it used to. Under normal driving, you can't even tell anything is wrong with the truck, it drives like it always has. The power loss is only noticable from about 3 psi-9psi of boost.

So what do you think, bad FMU?

 

Your thinking is very logical and sound. Replace the filter and verify your fuel pressure.
You would be better off ditching the FMU and going with larger fuel injectors and get a dyno tune. You would most likely see more power and better gas mileage to boot. Bob

 

ditto on ditching the FMU, larger injectors (42#'s +) and re-tune...
you'll be MUCH happier!

 

Can you point me in the right direction on what injectors to go with?

I gotta try and find a good place to dyno tune it. Its tough because its AWD and I can't just take out the front drive shaft. I'm basically gonna have to find someone who is mobile and will come out to a shop that does cars like Evo's and STI's.

I'll replace the fuel filter and post back up with the results. I might also try taking apart the FMU and see if the diaphragm is damaged. If so, I might be able to call ATI and get parts for this FMU. Even if I could just get the FMU working for a little while until I can save up some money for injectors and a tune.

Thanks.

 

you should be able to find a used set of injectors for no more than $250...
check over on performancetrucks.net classifieds...
the ones you want are GM Delphi Multec 2 High Impedence injectors
they are a GM Marine application...
they will be a direct fit on your truck...
OE part #25176061
37.95lb/hr@43.5PSI = 43.82lb/hr @ 58PSI

 

I agree with all the above.FMU is a band aid.I would run bigger injectors instead. We have a used set that just came off a truck last week.

 

I changed the fuel filter and there was no improvement.

I checked that part # @ work and it wasn't a good number. I work at a Chevy dealer, but I guess since its a marine part, its not avaiable to us.

How much you want for the used injectors Slowhawk?

I already found a place to do the tuning. There is a shop in my area called Speed Inc. (www.ls1speed.com) that can do the tuning. They can use the AWD dyno at a local shop that specializes in Evo's.

 

My only thought is that if you can make the fuel preasure go up at idle and you replaced the fuel filter but preausre will not rise when driving it maybe you fuel pump is getting weak and can't keep up the volume. I would consider looking into that before making the trip to the dyno. I am not sure how the fuel system is done on the truck procharger kits but I know the f body kit uses a Boost a Pump if the truck does to maybe you have a problem there. Not 100% sure because I don't know how that fuel system is set up.

 

Its not the pumps. The setup uses the stock pump in the stock location. The kit supplies a secondary inline pump that connects right before the fuel filter with factory style spring-lock fittings. Both pumps are working. In all of the fuel pumps I have replaced working at a dealership, I think I have only had 1 or 2 cases where they had low output. Usually a bad pump just quits period.

I e-mailed speed inc. (who I just realized sponsors this site) and this is what they said:

I'm gonna shop around because that seems awful expensive compared to what I have paid to tune my Mustang. I also don't want to install a wideband in this truck, I don't need it clutterd with gauges. I boost gauge and a fuel pressure gauge is already enough. Nor do I want somebody driving my truck on the street to tune it.

 

you need a WB more than you do a FP gauge...
you can get a column mount for it like I did or replace the FP...

in regards to the pump...I had a ProCharger inline take a dump...
trust me...you can ditch the FMU, upgrade the injectors, ditch the inline pump and replace the in-tank w/ a Walbro and be MUCH happier...
OR...you could do a hot-wire kit to the stock in-tank and use one of several voltage boosters available...either a boost referenced, FP exclusive or a TPS referenced overall booster...

 

Really $500 is not a bad price at all for tuning an LS1 on the dyno.

Also I work at a Dealership as well and granted I have seen a ton of fuel pumps just die but I have seen a weak fuel pump create drivablity issues on muliple occasions. plus I think that if you can make the preasure go up using your vaccum tester at idle(low volume) and while driving it will not go up(high volume) I think either you are not getting your boost refence to the FMU or you have a fuel pump problem.

 

Update:

Still trying to get the correct parts from Procharger for the FMU. I'm going to fix it for now and do the injectors in the spring. I got a rebuilt kit from them for $28, but one of the gaskets was wrong. I also dropped the piston that goes inside the FMU somewhere in the framerail/drivers motor mount area and spent an hour looking for it. I can't find it so I ordered a new one for $5. I'll get the FMU put back together and get it on the truck. My boost gauge is tee'd into the hose going to the bypass valve. I'm going to change all the hose out to silicone hose that I have and tee the boost gauge into the line going to the FMU. This way, I can verify that the FMU's needle valve is getting the boost it is supposed to.

I don't think that rebuilding the FMU alone is gonna fix it. I talked to John @ Procharger and he said usually the only FMU failure is external leakage. He said if mine wasn't leaking, it wasn't broken. I believe him because I cannot find any signs that the FMU was damaged after taking it apart. That is unless there was a problem with the old needle valve. The rebuild kit came with a new one that I will adjust per the instructions for the supercharger installation.

I realize that this FMU rebuild may be a waste of time, but when its done I will have less than $100 into trying to fix this problem, including shipping charges and the fuel filter. If there are fuel pump issues, then both pumps are gonna be ditched for a larger in-tank pump.

I'll update later when I have more progress!

 

FYI
We do street tunes as well and we temporarily hook up our wide band gauge to monitor the air/fuel. $500.00 for a tune. Bob

 

Really? When I did my turbo motor in my Mustang, my tuner mailed me a SCT chip with a base tune to get the car running and on a trailer. Then he dyno tuned it for about an hour on a very nice Dynojet dyno with the "eddy current" feature than actually puts a realistic load on the drivetrain so that boost builds properly. For all of that, I only paid $350. Not to mention he still helps me out to this day with any questions I have. That was not including the price of the chip.

With the HP tuners software for an LS1, you don't even need to buy any hardware from my understanding. You just are reprogramming the PCM.

I would consider $500 reasonable to dyno on an AWD dyno if a base tune was included to drive the truck to the dyno. In my opinion road tuning is out of the question. It is unsafe because you have to many things to pay attention to, plus in the end you are not getting a dyno sheet.

My truck already has a 02 bung welded in pre-cat on the drivers collector with a plug installed in it which tells me that somebody was using a wideband on it before at some point.

Anyways, I'd rather actually figure out what the problem is before I just dumping money into the truck. So, I'm gonna get the FMU back on the truck this week and go from there.

Thanks for the help!

 

$500 is the going rate so I wouldnt question that. I can understand being skeptical about road tuning but it is a viable option since there are not a huge amount of AWD dynos around and usually its done on quiet roads. If your really concerned about it though id say see if you know of an AWD dyno in the area and maybe have an ls1 tuner meet you there? I have seen a few sponsors willing to do this so it might be worthwhile to ask? Good luck though with the truck, looks sick from your sig pics!

 

Hmm okay. $500 it is I guess. Its more money to build a Ford but cheaper to tune it. Its cheaper to build an LS1, but more money to tune it. LOL

There is a well known Mitsubishi shop (AMS) that has an AWD dyno locally. Being in the chicagoland area, there are very few open, quiet roads around here.

Well, I'll cross that bridge when I come to it.

 

Well, I made some progress.

I created some of my own issues when I changed out the vacuum lines going to the FMU. It turns out that hose connector right by the needle valve has a orifice in it. I didn't know this, so I used it between the intake manifold and the stock fuel pressure regulator AND FMU when I replaced the hoses. This orifice is only supposed to restrict the FMU. The restriction caused a solid fuel pressure from my stock regulator.

I rebuilt the FMU, replaced all the vacuum lines with silicone hoses and ziptied all hose barb connections. My boost gauge was tee'd into the line going to the bypass valve. I changed that over to the line going to the FMU. So now I will always be able to tell if the FMU is getting proper vacuum/boost via my boost gauge.

Now that the FMU situation is sqaured away, I'm back at square one. Now my fuel pressure changes in relation to vacuum, but does not rise past 50 psi with boost. I re-checked both fuel pumps, just to be safe. With the stock fuel pump relay pulled, I have 0 psi key on. I should have at least some pressure with the ATI pump running and the stock pump disconnected, but I don't. With the fuel pump relay removed, I dont even hear the ATI pump turn on.

At this point, I need to get underneath the truck again and actually measure voltage at the ATI pump. I could swear that the ATI pump was running when I put my hand on it with the truck running when I checked it a few weeks ago. At least I know the stock pump is working. The ATI pump seems to be the last possiblility. I'm going to test it and see if that is the problem. If so, I'll have to see if its practical to replace the pump for now until I can afford a larger pump and larger injectors with a dyno tune.

Just an update for you all!

 

Good luck with it. Bob

 

Well, I pulled my head out of my *** and spent some time after work diagnosing the problem. With a clear head, and my Fluke 87, I found the problem in 10 minutes. The inline fuel pump that comes with the supercharger kit took a ****. I checked to make sure the relay was working. Then I crawled under the truck and checked for voltage at the pump, and its there.

I gotta call ATI tomorrow and see how much a pump is. I wonder if they will give me a part # for the pump so I might be able to cross reference the # and find one locally. The pump has a rubber jacket on it and I can't ID any part #s. It looks like it might be this one:


http://www.procharger.com/store/inde...d&productId=14

 

Just an update, the pump cost me $197 shipped from ATI. I threw it in and problem was solved. Only problem now is the new pump they sent is very noisy. It is by far the noisiest fuel pump I have ever heard. I have my stereo turned up over half way and I can still hear it from inside the truck. Outside the truck you can hear it from 100 ft away. ATI says its normal and wont switch it out for another. They just sold me this pump, and now they are recommending that I ditch the inline and switch to a 255lph Walbro. LOL!