Fuel pressure at idle and WOT

[orrum]

Hello diesel people! I am new to diesel trucks and this forum and have become very aware of the skill set and knowledge base u folks possess. I am n the prosess of getting my 91 GMC 3500 6.2 4l80e dually changed over to a wvo blend. I am installing a fuel pressure gauge b4 the IP this weekend as the first step. It would be a great help if I knew what fuel pressures u guys are getting???? Could u please tell me what ur filter system is? What gauge u r are usin as in electric or mechanical? What lift pump u are using? What ur pressure is at idle and WOT. Where ur fuel pressure is measured at i.e. pre IP or pre filter or wherever u got it from? Most importantly what fuel u r running? Such as Diesel, diesel with what additive, biodiesel, wvo, wvo blend, ugh maple syrup? LOL u never know! Thanks a bunch! This forum is a fantastic resource!!!!

 

[Crankme69]

Welcome to the forum.

Both my 6.5 vehicles measured with a temporary gauge hooked up at the Tee valve drain from the OEM filter manager running #2 fuel.

1995 1500 running a Walbro FRB5 lift pump 7lbs at idle & will drop to zero at WOT. Cruise is about 5lbs

1995 Tahoe OEM lift pump idles at 6lbs & will drop to zero at WOT. Cruise is about 4lbs.

HTH'd

 

[DZZ71]

Interesting, I'm excited to see how my raptor 150gph lift pump does at WOT.

 

[Burning oil]

With the newest Walbro I've been selling reports are 10-14psi at idle and 5psi at WOT. Mine is 12 and 5.

 

[Guster]

Not to hijack, but isn't the inlet pressure supposed to be 9 psi? Or did I mis-read that information. IF it is supposed to be 9psi, shouldn't it be that all the time?

 

[ak diesel driver]

ideally

 

[orrum]

Hey thanks everybody this is quite interesting!!!! Please all the rest of u out there respond we r plowing new ground here! Sounds like a mess out there to me,,,,, to give u my first impression I think Detroit err General Motors has a problem the way I see it. I am a newby but I could swear every reference I have seen to pre IP pressure has stated a minimum of 4 pounds????? Maybe the old pre 1994.5 Ford 7.3 with a DB2 aint better @ running wvo and cold northern diesel, maybe them boys got better lift pumps? Need more sample pressures please? Any u Ford folks feel free to chime in, I think we onto somethig here, preliminary analysis points to I need one of Leroys new fangled only he got em Walbros! Wow wonder @ .70 cents per pound how many beer cans I gotta pick up Leroy? LOL Thank yall in advance for responding!

 

[buddy]

The DS4 is supposed to have 6-9psi ideally, but GM messed this up with their lift pump choice, although it works alright with stock programming, but even stock feels more responsive with higher fuel pressure. A better lift pump is pretty high on my recommended modification list. There are several pumps that can get you there, but Leroy's Walbro is a fine choice for value. The DB2 4911 turned up all the way could likely use the same, other models not so much needing it.

Are you planning to run only WVO, or is this thread more like youre just trying to get the whole thing set up right. Because I imagine you need a whole other tank with heater and other pump and filter setup with a solenoid tieing it in before the IP and you switch from diesel to WVO. Since you dont want WVO solidifying in the IP, which means you need to switch to diesel fuel for like 10 minutes before shutting down.

If you are still using the OPS to run the LP make sure to do the OPS relay mod.

 

[orrum]

Hello Bubby. Heres the deal, I run my 1975 Mercedes on a single tank blend of 80% wvo with 5% regular gas, 10% k-1 kerosene and 4 oz. of power service diesel kleen plus I have electric resistance injection line heaters. Had the Mercedes on the blend for 10,000 miles and no issues and bought the 1991 GMC 6.2 non turbo to specifically switch to this blend with some differences being a fuel pressure gauge so I dont kill the IP with clogged filters and bad lift pump, another is to put a spin on filter in the engine bay to keep the square stock filter clean, and of course electric resistance injection line heaters. Will start with this but I am guessing at this info on lift pumps from yall I will need to have one of Leroys Walbros and a prefilter almost immediately from the way u guys r responding with these pitiful pressures. The previous owner must have taken the mechanical lift pump off and now it has a electric one under the cab on the frame. Oh and I definitely am gonna run it on wvo, my neighbor adopted my system and now runs his John Deere tractors for his farming operation on wvo, hes been on it for a year now too. Its all about ur source of wvo, I get mine from a catering outfit that I managed prior to my accident and loss of my leg, worlds greatest cowboy my friend. At the catering business we never filtered the soybean frying oil like most folks do, instead to get really great fried chicken we changed it out when it needed filtering so its not all brokken down and full of emulsified water plus a lot of folks put the oil n the big tank with the water they use to wash the big fryers out and we dont. Anyway its really easy to clean the oil and they have way more than enough to supply me and I need to run the truck on it so I can afford to pull my horse trailer to the weekend rides and camp. Hey I like my old GMC, its a nice truck but she gotta burn veggie oil! LOL U guys r gonna help me make this work cause I done figured out those guys on the wvo forums are way lost in the chemical end of burnin wvo, what is needed here is technical diesel 6.2 experience and yall got that in aces! LOL Like the Walbro on the frame with a prefilter and feed the beast etc. The 6.2 non turbo is supposed to be the toughest engine around to burn wvo if u can get past the IP crapping out problem and I really think the answer to that is on this forum. Anyway thanks and if anyone has more info on pre IP fuel pressure let me know please? After I install my pressure gauge I need to change my oil and fuel filter and I cannot find directions on here to do it I think the square filter has some quirks, should I ask now how to change the fuel filter or is it better to start a new thread? I can handle the oil change part! LOL At least I hope I can. Any quirks about a 6.2 oil change?

 

[orrum]

Look here are the facts to what I want to do with my 6.2 and any advice from yall is good. I need to pull my goose neck horse trailer, its a 1971 WW with a homemade living quarters, weight unknown but I pulled it way back when with a 1980 half ton Dodge D 100 with a 318 and a 747 long tail transmission, never tried the mountains with it, then switched to a FANTASTIC 1985 454 Gmc dually that could of pulled the hinges off he$$ but got 7 mpg at best and only 5 towing n I swear n the mountains with her kickin for all she was worth u could see the gas gauge go down! I dont care about mpg with my 6.2 if I run it on wvo its less than a dollar a gallon. Back to the subject, the trailer and two horses shouldnt weigh more than the 8000 lbs. that the 80 n 4l80e transmission stands for. I am going to put the biggest transmission cooler on that will fit behind the grill. Hey its only $60.00 @ NAPA unless yall know something better. If this works out I want a huge fuel tank n the bed so I can go places and get home without refueling. I wonder about a better air breather system and exhaust. Now dont go crazy with mods that cost money, I want to do them all but I need to do what is absolutely nesessary first and then prioratize by most effective and easy and cheap first. Thanks again. Oh by the way the trail rideing season is best in the fall and spring here in NC due to heat and biting flys, so I got till Sept. to get this done but to b honest I want it done in the next few weeks so I can play with it close to home b4 I take off on a long trip with the horses and girl friend, she panics bad when u start the roadside repair routine! LOL

 

[bison]

If you get a couple psi at WOT or under load on a stock engine and a stock LP i would not get too paranoid about it.
These engines have been doing well with that for the last 20 yrs.

My 2 c

 

[handcannon]

One of the cheapest mods you can do is the snorkle delete for your intake air. The stock filter box sets on the pass side inner fender and is set up to pull in air from the fender. If your pickup is still stock it will have a plastic tube that looks kind of like an elephants trunk inside the fender that runs forward to right behind the headlight. This snorkle is very restrictive and removing it will increase the air available to the filterbox. I have never seen one (just pics) since somebody prior to me already removed the snorkle on my pickup. However, if you do a search on this site you'll find all the info you need about the delete.

On the exhaust end I went to a Diamond Eye system. It is a 3" turbo downpipe, to replace the crushed and very restrictive factory downpipe, and 4" pipe and straight through muffler to replace the rest of the factory system. I got my DE system from TV Diesel out of Idaho for less than $300 shipped. It's an easy system to install and along with the snorkle delete one of the best mods outside of cooling you can do for towing.

One other thing very important for towing is to never let the coolant temps go over 210*. A very cheap thing to do that I would reccommend is that you very thoroughly clean the cooling stack (rad, AC condensor, tranny cooler, and engine oil cooler). Start by very thoroughly flushing the cooling system first. Then remove the radiator and clean the exterior of the rad and the AC condensor and oil coolers. This area has a tendency to build up "birds nests" of crud, creating cooling problems.

Another important part of the cooling system is the water pump, fan and fan clutch. I have a 94 pickup which probably had the same fan clutch that is on your pickup. Over a few years of use the clutch loses a lot of the "liquid" that makes the thing work. If the front of the unit looks like it has all kinds of dirt and grease on it you can be sure the clutch is no longer going to be very effective since this "liquid" is migrating to the outside. The older clutch has six bolts holding the fan on and four bolts to the water pump. Some time around 96 that changed to four bolts holding the fan on. This four bolt pattern is the same as the newer DMax fan. Then sometime around late 99 or 2000 the pump mount changed to a threaded hub.

With an all stock system (including a weak fan clutch) I was having overheating problems. To go to the coast I have a 2000' pass to go over. To go to the high desert of central and eastern Oregon I have a 5000' pass. And the I-5 corridor of south western Oregon has several 2000' passes. I tried just changing to a severe duty clutch and the DMax fan, unsuccessfully. I ended up with the 2000 model year high output balanced flow water pump for $175, DMax fan for $55, and Heath Diesel's low temp heavy duty clutch for $200.

I fully understand your concerns about costs of the neccesary mods as I'm having to do all this and survive on SS Disability. If you have any questions about how good of condition your cooling system is in I'd personally spend the money on the cooling system first before anything else, especially since you are towing.

There are other mods you could do, but I feel these are the most important for towing.

Don

 

[great white]

Interesting, I'm excited to see how my raptor 150gph lift pump does at WOT.

My raptor 100 does 15 at idle and 12 with right sole hitting floor.....

 

[buddy]

If you get a couple psi at WOT or under load on a stock engine and a stock LP i would not get too paranoid about it.
These engines have been doing well with that for the last 20 yrs.

My 2 c

Some people might not call what their 6.2/6.5 has done as being well

I think the only problem running 80% WVO would be in the winter, when you might need to run the block heater and get the injection pump itself heated before starting. Certainly doable.

You will likely be disappointed with a NA 6.2 in towing, because the 454 and even Dodge 318 will run circles around it. Now, add a turbo and turn up the IP and you'll get up to 454 power on diesel and twice the fuel mileage. Although youll have less power/mpg on WVO. Here is a file of things I recommend, some are low cost modifications, and you can ignore the PCM/PMD stuff. Of importance is OPS relay mod, because I think you always had electric lift pump that runs of the OPS. Check the passenger side firewall for the LP fuse and relay. That, the exhaust, air filter box, and lift pump are best mods before going to the turbo. Of course I agree with previous psots on the cooling system, which is also detailed in the file.

 

[orrum]

Ok the fuel pressure gauge install is not happenening today, my Fastenol needle valve does not fit my grease hose that i am using to isolate the sender. Back to Fastenal Monday.

 

[orrum]

Hey Handcannon and Buddy, Great write up! Got some info 4 u on my 6.2 dually. The exhaust pipes come out of the engine at a small size and then where they come together its one great big pipe, I guess 3 inches that goes to a muffler that has two small pipes come out and go all the way to where they come out behind the rear wheel, is that a good enough exhaust???? Also under the hood is a plastic cover with fuel pump fuse on the far left next to ground and then on the far right is written fuel pump relay. Take the cover off and on the left is a small black plastic module with a plug in, is there a fuse inside that thing or is the whole thing a fuse? Is this the setup I want 4 a electric pump? I notice that after I turn the engine off u can hear the pump run for a few seconds but I never hear it run during the glow plug cycle, does this mean I need to do the mod to get the pump to pressure up during the glow cycle??? If so my retarded cowboy self doesnt understand ur directions in ur article could u break it down 4 me please? Next thing is the electric fuel pump under the truck it sure looks factory to me, it has AC on it and over to the side says EP158, is this the factory one? Is it good enough or should I start collecting aluminum cans to get one from Leroy??? LOL U know I really cant c under the intake to c where that fuel hose line thats blocked off comes from and I definitely aint tall enough to get to and examine my square fuel filter, how do yall crawl up n there without knocking and breaking all kinds of stuff? LOL I am 6.2 tall, get it 6 ft 2 inches tall like my motor LOL anyway with the artificial leg I might really tear it up. Do yall put a sheet of plywood up there for a platform to crawl on or what? I am serious here folks! On the radiator, its definitely clean cause its brand new, I just had it put on cause the old one was rotten. The fan blade according to the radiator shop is working properly. Radiator shop flushed the coolant system to get rid of the previous owners liberal stop leak use! The ac condenser n front of the radiator seems to be all gummed up on one side and the other side looks nasty but isnt as bad. Suggestions to clean or dissolve the mess would be appreciated. On the air cleaner, it has a plastic tube with a big bulge connecting the snout of the air cleaner to the fender wheel. I just pulled the plastic stuff off and stored it in the shop, this leaves the round metal part with the two wing nuts with a short snout ticking out. Should I put screen wire over the end of the snout to keep varmits out? The air cleaner is brand new by the previous owner and looks good but do yall have a reccomendation for one that will both keep the air clean and let it breath better????

 

[buddy]

So in 91 you have the air cleaner on top of the engine, perhaps all 6.2s are that way stock compared to the 6.5s that started in 92 with panel filters by the fender. Unless you go the route of a turbo addition then that one should be fine, although you should keep the plastic that goes to the fender, but there is a plastic piece inside the fender that you can pull out to help a bit. I also assume this one has holes in the bumper where the air is supposed to come in and directed to the fender. The exhaust is also alright unless you go for the turbo addition.

You dont have to add fuel priming during the glow cycle, but it can help startup, although its really best to get the LP power off the OPS, which is why you use a relay, that is triggered by the OPS. The diagram is just showing how to hook up the wires that go to the OPS to a couple regular 5 prong relays, although if unfamilar with relays then it may not be easily understood. The diodes and resistors are not required, just drawn in for those interested. Kennedy Diesel sells a kit for this purpose but its like $140. A couple of relays, a pack of crimp on connectors (blade, ring, and butt) and some wire for $15-20 can get you the same thing. Leroy might be willing to make you a custom OPS relay mod harness like he did for his own Suburban (plug and play), but I imagine it would cost about $80 for the whole kit with relays.

 

[Burning oil]

Sound like your truck is all stock and factory, the LP is stock on yours. I would continue using it with the WVO blend and save up in the mean time. Its just a matter of time before it go's.
My brother has a ladder looking thing that has a platform you can lay on/across the top of the engine. I keep thinking I need one. Your truck should not have the holes in the bumper like the 6.5's do. They make great foot holds, most of us just step up in those and lay down on the fan shroud area.
You can put a screen over the air filter opening or just put the plastic works back on. You do want to remove to retrictive (if you have it) snorkle inside the fender though.
I have a right up here on the way I did the OPS relay mod. http://www.thetruckstop.us/forum/showthread.php?29787-OPS-Relay-Mod.-Slightly-different
If you just absolutely need me to build one let me know. I do not have an old OPS to canibalize, so you would need to send me one.

 

[handcannon]

The exhaust pipes come out of the engine at a small size and then where they come together its one great big pipe, I guess 3 inches that goes to a muffler that has two small pipes come out and go all the way to where they come out behind the rear wheel, is that a good enough exhaust????

how do yall crawl up n there without knocking and breaking all kinds of stuff? LOL I am 6.2 tall, get it 6 ft 2 inches tall like my motor LOL anyway with the artificial leg I might really tear it up. Do yall put a sheet of plywood up there for a platform to crawl on or what? I am serious here folks

On the radiator, its definitely clean cause its brand new, I just had it put on cause the old one was rotten. The fan blade according to the radiator shop is working properly. Radiator shop flushed the coolant system to get rid of the previous owners liberal stop leak use! The ac condenser n front of the radiator seems to be all gummed up on one side and the other side looks nasty but isnt as bad. Suggestions to clean or dissolve the mess would be appreciated.

On the air cleaner, it has a plastic tube with a big bulge connecting the snout of the air cleaner to the fender wheel. I just pulled the plastic stuff off and stored it in the shop, this leaves the round metal part with the two wing nuts with a short snout ticking out. Should I put screen wire over the end of the snout to keep varmits out? The air cleaner is brand new by the previous owner and looks good but do yall have a reccomendation for one that will both keep the air clean and let it breath better????

On your exhaust, I was thinking turbo exhaust and obviuosly you don't have a turbo. My bad!

Your description of your exhaust sounds good. My big question would center around the two smaller pipes exiting the muffler. Are they at least as big of diameter as the downpipes coming off the manifolds? As long as they are the same diameter, or larger, you are good. Having a larger diameter after the muffler than what is coming out of the manifolds is better as this will reduce backpressure. Backpressure in a diesel is what we want to reduce.

Your next question about getting up into the motor compartment to gain access to components that are way up there is a good one. I have a severely compromised back and using the bumper to step on and then being on hands and knees on top of the motor to access things makes my back hurt. Several years ago I saw a pic of a special ladder/frame that would make things better in both our cases. I'd forgotten about it and your question about using a piece of plywood reminded me of it. I'm going to have to see what I can come up with and build one.

It sounds like you are one up on the cooling system. The biggest thing you are going to have to deal with is upgrading from your current system if you have any problems with overheating. This is where the system I described that I put in my pickup would come into play.
I got my pickup as a rebuilder so I had to replace the engine oil cooler, AC condensor and radiator so I have no hands on experience with cleaning the condensor. However I've read of people using Scrubbing Bubbles and/or Simple Green. Take and use an air hose or garden hose and blowing from behind carefully blow out as much crud as possible. Then soak down with a cleaner, let it soak, then flush from behind with water. You may have to do this several times, depending on how caked in there the crud is.

On your air cleaner, I'm in the same boat here as buddy. I thought you would've had the same flat panel filter system that is in the 93 and 94 vehicles. Your description sounds more like a filter canister that is like the old round types that can be found on carbed motors, and the 80s era 6.2 vehicles.
From your description, taking off the inlet as you describe, leaves the end sucking in underhood air and not directly from inside the fender. This will be hotter air than what would come from the inner fender cavity. Not good.
As buddy said, the plastic tube that is INSIDE the fender is the one to be removed. The tube from the filter canister needs to be connected to the fender, AFTER the plastic snorkle is deleted from inside the fender. Using as large of diameter tube between the filter canister and the fender as possible is important for proper air flow to the motor.
Being hooked up to the fender will bring in cooler air from behind the headlight. Cooler air is more dense, thus packing more combustion air into the motor. Air is kind of like a sleeping bag. If you wad it up (hot air) it takes up a lot of space. But if you roll it up tightly it is the same sleeping bag in a more condensed (cold air) package.
What is the diameter of the opening in the filter canister? On my 83 6.2 pickup it was about 2" in diameter, not good. I redid my 83s' filter canister to be a four inch inlet. My 83 6.2 pickup didn't bring in intake air through the fender cavity. Instead, it had a flex tube going from the filter canister directly to an opening in the radiator support, right between the headlight and the radiator. This was just like todays ram air systems that you can get, the faster you go the more air is packed into the intake.
Could you post up a pic of your current intake air setup? I'm just curious how much of it is like the one in my 94 pickup and how much like the one that was in my 83 pickup. This could be helpful with suggestions for improvements.

Also, do you have the eqiupment and ability to do any fabbing? I actually did way more fab work to my 83 6.2s' intake than I described and am wondering if you might be able to do some of the same. It made a difference according to my butt dyno.

Don

 

[orrum]

Overload of my brain but we r gettin there! So to summerize my exhaust will do the job as good as can be the way it is. The intake air filter system needs to be put back on but reach in the fender and remove the rubber like thing that blocks the air getting n 2 the big plastic snout. The electric fuel pump is ok and also factory so I have a relay etc and thats very good. now this is where I get confused, why do I want to do the ops mod? I thought it was to get the pump to pressurize when the glow plugs come on but in Leroys tutorial he said he didnt need it for that cause he started just fine. Buddy u said its better if the LP runs off the ops, why is it better? I can tell u the blend wont start as easy but in the John Deere tractors they start great even @ 20 degrees. We had a really cold spell around xmas this year so I know that for sure. Usually never freezes water in the horse water troughs. Leroy if I need the OPS mod I am willing to do it myself, hey yall talked me thru the TPS fiassco didnt u! LOL I barely understand relays but another great guy on here is talking me thru a way to use a relay for my electric resistance wire injection line heaters. I am gonna do that one too, hook the relay up so I can turn my ignition switch to accessory for two minutes to let the injection line heaters warm the wvo in the lines up then turn the switch to glow and then start her up! I am supposed to hook the relay to the radio fuse cause it comes on with the ignition turned to both accessory and when on for glow and for running, I think thats a real winner, see those wvo guys dont have that kind of skill set. Plus until I switch it all these things will make it better for towing no matter what fuel. So Leroy I still need to put a filter in front of my electric lift pump right? So do whatever u do to sell me a set of those screw hose barb adapters that I use to add a filter into this thing and by the way there is a cheesey lookin plastic circle clamp thing supposedly holding the lift pump to the frame but its broke the metal fuel lines r holding it so I will be trying to copy ur walbro and filter mount deal on a post I found of urs. Thanks Leroy and Buddy, wow I feel pretty good about this, makin progress! I will get the air intake corrected tomorrow and study this OPS thing and try to understand it. Where do u buy relays? Radio shack? I got the wire and all kinds of crimp stuff, gotta wire up the trailer plug in and brake controller yet. Let me guess yall got all kinds of ideas on that one too! This one I done several times b4.