1998 Yukon How to test fuel filter/Weird pressure readings.

[OilBurner2003]

Hello everyone! Have been trying to fix this pressure and misfiring issue of mine for a while! Just did the injectors last night, (Didn't do a test because it was late,) Woke up and checked the pressure and it was still at 55, but running Decently, I'm no longer losing fuel pressure so at least I was fixing that problem, took it for a test drive. Did pretty damn well. Came back home and wanted to test FP again, shaky idle, p0300 showed up, acting just like it did before the injector change. Key ON 60 PSI, Engine Idle PSI 55-54. So what does that tell me? Fuel pressure regulator, Pump, Injectors, are all new. Something to note is I installed the Multi port upgrade. Doing the injectors did fix my fuel pressure leaking problem, now I can't figure out why it's not getting to at least 60 idling. My only other thought is that it could be the fuel filter? We did that like a year-2 years ago. One of the fine gentleman on here gave me a whole instruction guide to test it but I don't have the right fittings. Does anyone know how I can test a fuel filter, or is it the type of thing I throw in and see if there's a change? It's the only fuel related component I haven't looked at yet.

Before my work and after, I have never seen this gauge hit 60 PSI idling, Or anything above 55.

Update, New filter and idle is almost perfect, only slight vibrations which is probably something else, Fuel pressure key on is now 62, Idle is 57, Accelerates well! Have to go stress test it today, gonna go floor it up hills and try to get that code to show up! Praying it doesn't. Most importantly I'm not losing fuel pressure when I leave the gauge on when key is off, here's hoping my P0300 issue is finally fixed! Will update on how it does today.

 

[OR VietVet]

Get your line wrenches out and change it and then retest. The frustration you are experiencing is not worth the hassle. Get a good Wix filter like the link I supplied and change it. It is easy and inexpensive. Did you see ANY debris in the tank when you did the pump and what did the sock/screen look like on the old pump you removed. If you have air, unhook the lines at the tank and at the injectors and when doing the filter, blow those lines out to make sure you have no restriction. Is there any kinks anywhere?

 

[OilBurner2003]

Get your line wrenches out and change it and then retest. The frustration you are experiencing is not worth the hassle. Get a good Wix filter like the link I supplied and change it. It is easy and inexpensive. Did you see ANY debris in the tank when you did the pump and what did the sock/screen look like on the old pump you removed. If you have air, unhook the lines at the tank and at the injectors and when doing the filter, blow those lines out to make sure you have no restriction. Is there any kinks anywhere?

Taking out and replacing fuel filter today, old pump screen was a little dirty. Although 20+ plus years tends to gunk stuff up. You’re referring to the lines that go into the spider injector bracket, correct? The ones by the cap and rotor?

 

[OR VietVet]

Yes. You don't want to blow in to the injectors. You want to disconnect where the feed line supplies the fuel to there. You want completely open lines from both sides of the fuel filter connections. DO NOT blow into anything that connects at the ends of those two lines.

 

[OilBurner2003]

Yes. You don't want to blow in to the injectors. You want to disconnect where the feed line supplies the fuel to there. You want completely open lines from both sides of the fuel filter connections. DO NOT blow into anything that connects at the ends of those two lines.

You know, and I’m not sure why I’m remembering this now, but when I removed the fuel lines to do the injector job I thought I saw some discolored fuel. I can’t be 100% sure with the lighting I had, but that would explain some things as well…Gonna drain the fuel in the lines and get to work!

 

[OilBurner2003]

Yes. You don't want to blow in to the injectors. You want to disconnect where the feed line supplies the fuel to there. You want completely open lines from both sides of the fuel filter connections. DO NOT blow into anything that connects at the ends of those two lines.

Looks like the filter made a good improvement, Idles much smoother and so far I can't get p0300 to come on, but we'll see after some driving. Funny thing, Fuel filter nut to the gas tank side was actually not snug, could move it with my hand. I have no clue how it wasn't leaking! Good thing I thought about all this lol, New wix installed.

 

[OR VietVet]

Funny how sometimes basics do the trick. Please drive it and report back asap.

 

[OilBurner2003]

Funny how sometimes basics do the trick. Please drive it and report back asap.

Went for a drive and it seemed really good, Although now I am staring to wonder what's going on now, and if this is what I've been trying to track down the whole time. When the engine is cold is idles really well, when it's warm it gets rough. Because the only thing that changed during my test drive is the engine temperature. it's to the point I think a misfire code will show up but it hasn't yet, checked all my work, wires, plugs, Fuel pressure test which are still within the ranges I updated earlier, there's really not much I haven't diagnosed which I KNEW was bad. I'm not sure how to check the IAC or if this would even affect it for the symptoms I'm having, however, I did notice something really strange. When you give it some gas, The rpm's go up, but when they go back down it acts like its catching up, like they were getting too low for a second. I did hear that the distributor vent screen can cause problems like this, I'm just not sure what it looks like or where it is. I'd imagine it's underneath the cap and rotor?

 

[OR VietVet]

Yes, the vent screen can cause problems of dist cap tabs build up and that can cause a misfire. Screen location is in the bottom metal plate of the distributor. If do a cap, always do the rotor at same time and get quality OE aprts and not aftermarket crap. The IAC is pretty easy. It will be at the driver's side back corner of the throttle body housing. Will have a plug in. Unplug and use a large wrench or socket to unscrew and remove. The object of this part is to control air flow mixture with the fuel for different load conditions and does play in to what you are experiencing. Carbon can build up badly in the post area. Will need to use carb cleaner and a small wire brush to clean and to clean evenly, use a tapered round wire brush like is used for cleaning the inside/female part of a battery cable end. The cleaned can also be used on the adjustable spring loaded rod of the IAC but I always just replace the IAC. A cleaning of it can work in the short term but typically the damage is done and the problem comes back. At end of rod, if you try to clean, is a tapered end that goes back and forth in the port of the throttle body and that can be cleaned as well.

https://www.rockauto.com/en/moreinfo.php?pk=88851&cc=1305076&pt=6072&jsn=896

More Information for DELPHI CV10011

I just wish your system would set a code for the rough idle when engine is war. It could be the IAC and could be related to a MAP and/or MAF and even a Air Intake Charge Temp Sensor.

https://www.rockauto.com/en/moreinfo.php?pk=1821902&cc=1305076&pt=5072&jsn=926

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What I really wish had been done, while you had all the plugs out, is a compression test.

 

[OilBurner2003]

Yes, the vent screen can cause problems of dist cap tabs build up and that can cause a misfire. If do a cap, always do the rotor at same time and get quality OE aprts and not aftermarket crap. The IAC is pretty easy. It will be at the driver's side back corner of the throttle body housing. Will have a plug in. Unplug and use a large wrench or socket to unscrew and remove. The object of this part is to control air flow mixture with the fuel for different load conditions and does play in to what you are experiencing. Carbon can build up badly in the post area. Will need to use carb cleaner and a small wire brush to clean and to clean evenly, use a tapered round wire brush like is used for cleaning the inside/female part of a battery cable end. The cleaned can also be used on the adjustable spring loaded rod of the IAC but I always just replace the IAC. A cleaning of it can work in the short term but typically the damage is done and the problem comes back. At end of rod, if you try to clean, is a tapered end that goes back and forth in the port of the throttle body and that can be cleaned as well.

https://www.rockauto.com/en/moreinfo.php?pk=88851&cc=1305076&pt=6072&jsn=896

More Information for DELPHI CV10011

Will do that now! Do you have a picture of what the vent screen looks like? I can't find it anywhere.