Fuel Delivery?

[vwtipeii]

Hi gang,

I know you will all make fun of me for still not having my lil YJ fixed and running so keep the peanut gallery comments to a minimum here please. Bottom line Everything possible has been done to my lil YJ's new stroker to try to get her to run cool. she still gets hot under load. She does run a tad lean so the last hope is to dump more fuel in her. The ECU controls fuel delivery though and that can't be changed. Any ideas how to increase fuel delivery? I already have 24lb injectors. Do I got with an adjustable fuel pressure regulator and crank it up? Even if that is done won't the ECU still monitor or change that? I have had several shops try to fix it... i am at my whits end and its been a 2 year struggle. The cooling system is more than enough for the job.

I know i should have just gone with an LS..however i am not now so I don't need that recommendation.

As a reminder my YJ is a 94 with OBDI... not OBDII

Thanks,
B

[6spdYJ]

Hi Brett,
After I wrote this book, I have to ask, have you replaced your knock sensor? If the knock sensor is working properly on OBDI, it should allow a bit more fuel to be delivered per injection by extending the dwell time of the injectors by a millisecond or so. If it's not working your ECU might not realize there is i problem - just a thought. Now, back to where I started.
What fuel pump are you running? The injectors are basically like a shower head, they are rated to flow a certain amount of fuel in a wide open condition at a specific pressure. The YJ pump is at a lower pressure than the TJ pump and is possibly not atomizing the fuel enough as it injects.
Think of it like this: start with a medical syringe with a body 1/2" wide and a stroke of 2". Fill it with water, point it at the ceiling and put two pounds of pressure for a half of a second on the plunger. The water shoot into the air.
Now fill and hold it the same way. This time, put the same two pounds of pressure but keep pushing for one second. The water will likely hit the ceiling. This would be the effect of changing the injector dwell time, as nothing has changed except the duration of the pressure being allowed by the injector. This can be tweaked on a YJ with an adjustable MAP sensor. Many turbo specialists know about these items and can dyno tune your rig to run best with them.
Now, lets go a bit further with the injector experiment. Start back at the original syringe scenario with the plunger travelling two inches in half of a second. Remember how high the water went?
Now drill out the nozzle end of the syringe to, for the sake of conversation, 1/4". What would you expect the water to do now - with all other conditions the same?
The water would be easier to push out of the bigger hole, but wouldn't go nearly as high. This is the same as putting in a bigger injector without changing the pressure supply.
Now, let's fill it again and push the plunger two inches in one thousandth of a second. This is the effect of a bigger injector with more pressure.
Back to the adjustable regulator, it can only allow as much pressure as is available from the pump to reach the injectors. Consider it as a limiter. For the sake of conversation, it will allow a 39lb pump to deliver 39lbs - only at wide open throttle, but only at wide open. At partial throttle it is set to deliver say, 29lbs (completely arbitrary numbers) It reacts to the lack of manifold vacuum and an internal spring pushes it open. An adjustable one allows the partial throttle pressure supply to be increased to a set point, say 33lbs. Now, what if you need 38lbs on a flat road? You're set - until the first hill... Now you can only deliver 39lbs at WOT. With a properly sized pump that can stand up to the injector demand, and a regulator set to limit partial throttle pressure, you can be sure you have what you need to feed this beast.
The mind numbing stuff... Then we need to know, what compression ratio are you running and what is the camshaft? Cylinder compression - and even piston crown design play a huge part in how heat is transferred into mechanical energy. The camshaft determines how much air is allowed into the cylinder - and when. The when also plays a big part in dynamic compression as well as how much fresh air is in the cylinder to mix with the atomized fuel (there is always a small amount of leftover exhaust in each intake cycle). You can also look into running a "cooler" spark plug. These effectively transfer heat from the plug into the head - and cooling system a bit faster. It can help to remove just a smidgen of heat that's left-over from the last power cycle. This is more for the final detail, dyno type tuning but may possibly help reduce pinging.

[Zoobi]

Did you have it checked on a dyno? If your fuel pumps not putting out the volume as 6speed said, there's an easy way to test it. You can put the regulator you mentioned in and crank it up, if it gets better you need bigger injectors. The other way is, using pliers designed for hoses (special so they dont kink) pinch off return and drive it. if its better you need injectors, if not then its fuel volume (pump, lines). The pcm does control the injector but if its the wrong size, it wont meter fuel correctly.
The only way to find out what exactly is happening is to put it on a dyno with a gas analyzer. If the test shows your very lean then you play with injectors. The other issue can be (but not likely) is your pcm isn't powerful enough to work the aftermarket injectors. Your compression may be too high also.

As we discussed in calico, you need a base starting point. If you take it to a good dyno shop your going to need all the engine info, cam profile, compression... The problem your faced with is the people who are looking at your problem have no experience diagnosing this type of issue and are not equipped to do anything but guess and throw parts.

I wish I was allowed to bring your vehicle into my work and throw it on one of the dyno's(i did ask). We purposely cause these kind's of issues for diagnostic training. One of the instructors at my shop has a relative who owns a very good tuning shop. I don't know if they would look at your jeep but if you want I could get their name and you could call and see.

Scott

[vwtipeii]

Thank you gentlemen. Josh at leadfood tried to take the YJ to a shop for the power pulls however a rocker started coming loose at the time and that made a horrible ticking and they couldn't actually do any full pulls on the dyno. IF you guys have any dyno shops around you recommend just let me know!!!

Thanks,
B

[Zoobi]

So you fixed the rocker and brought it back, or you still have the issue with the rocker or? You had mentioned this in Calico I think but I don't remember.

A misconception with dyno's is people think you only "do power pulls" for horsepower/torque. While that's the is one of the many things that can be done, using it to put a load on the engine while diagnosing is what I'm referring to. The one that I know of is out in Riverside somewhere, and again not sure if they will take yours in.

If the shop you referred to in your post is capable of doing this it may save you some phone calls. What you have to look at here is not that your Jeep is broken because it probably isn't. Broken would be, your Jeep was fine until... What you have is a mismatch of parts. That means its going to take someone alot of time to narrow down what is lacking and modify from there.

A typical shop can fix whats broken and or bolt parts on and hope they match. If there's an issue, their knowledge goes only as far as testing parts and comparing them to a spec (assuming they know how to do this). On your vehicle the "spec's" cannot be found in a book because it's custom, one has to know what everything is suppose to be and what it takes to make it. That just eliminated 95% of the shops out there. No one can assume anything is what its suppose to be. So you need a baseline.

Bottom line, some of the dyno-tuning shops will deal with this as long as its injection related and tune your fuel accordingly. Your issue screams lean mixture, which by the way is very common on modified vehicles. If its not Fuel related, it's still a step in the right direction. You have to have the issue narrowed down. What your looking for isn't someone to see how much power but to see how the fuel system is working under a load.

I will get the name of the shop I mentioned on Monday and send it to you. If they wont take your vehicle, they may know of someone who will.

Scott

[vwtipeii]

Thanks Scott... perfect.

[vwtipeii]

well.. a little progress has been made. Josh finally got it to a dyno shop that has the appropriate equipment to read the air full mix under load. It appears the jeep runs just fine under normal conditions under 200 degress and when not under load, and she runs fine at WOT. However, any time the Jeep is over 200 degrees and under partial throttle..she runs lean. We we put in the stroker we didn't upgrade the fuel pressure regulator or the fuel pump. A few calls and 505 who build the engine is sending their adjustable fuel pressure regulator overnight tonight Josh with the hope we can get it installed tomorrow and back to dyno on Friday am.. home to pack up Friday night and hit the road at 4 am Saturday to enjoy Memorial Day weekend out with Tom Severin and crew. We are not out the woods yet but this is a step in the right direction.

Thank you gents for all the feedback and ideas. I don't know why I didn't do this when the engine was put in originally..but lesson learned...

B
and had some dyno numbers... not happy with them.. but will share anyway; 165 hp and 215 torq. Will try again with more fuel and should be much better... I hope!

[6spdYJ]

Sounds good. As far as the lean condition, an adjustable MAP sensor makes the ECU think there's more air, so it allows a bit more fuel. A regulator might help a bit, but the MAP sensor will stretch out the time the injector is allowed to fire. Since it isn't lean at WOT - the condition the stock fuel pump is allowed to run at full pressure - it sounds like your existing pressure is fine.

[Zoobi]

Good Deal.
Sadly it's the simple things that kick us hard. Most people with modified fuel injected engines stop after the injector up grade. While this will be fine for most people, they don't realize the engine is not running well. As you noticed, the system had to be tested under the circumstances that the problem occurred. I'm glad your going in the right direction. A little bit of tuning and you will notice some higher numbers, most likely torque. But those numbers to the ground look like what I would have expected.

Scott