What could it be.......

[kennythewelder]

Fuel pressure needs to be over 60 PSI, key on pre start. Any thing else is low fuel pressure. 58 is low. I just replaced my fuel pump today. It was at 58. Also I agree with spider issues, leaking fuel pressure regulator it is on the side of the spider. You can get creative, and pull the throttle body, then jump the fuel pump relay, so that the fuel pump stays on, and look inside of the intake with a mirror, and a flash light. I have done this on my 97 5.7L. you can see all of the spider hoses, and the fuel pressure regulator. Although this is a long video, it tells you how to jump the relay and keep the fuel pump on, while you check things.

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[stutaeng]

Um, I thought spec for these was 58-62 psi?

I believe the poppets need a higher pressure to start than to run. So if his engine is starting fine, then likely not a fuel delivery problem. Otherwise it would not even start.

Of course, it could be below spec., but not the problem to his question.

 

[east302]

Here are the diagnostics for 1998 for P0174, maybe it will help.

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[kennythewelder]

Here are the diagnostics for 1998 for P0174 and P0300, maybe it’ll help.

Edit: the images below don’t show up when I view my post. If it’s not just me, let me know and I’ll try to PM them to you.

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And P0300...

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Cant see any of your pics.

 

[east302]

Yeah, I don’t know what is wrong with it but it isn’t cooperating. I tried to re-post it a few times and now it’s all sideways.

To the original poster, GM has diagnostic tables in the factory manual for each code which is what I tried to post for you. I’d run through the P0174 and P0300 tables and see what that does for you.

PDF scans of the 1998 manual can be downloaded here, DTC tables are in volume 3.

https://www.gmt400.com/threads/88-95-service-manuals.43575/


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[kennythewelder]

Um, I thought spec for these was 58-62 psi?

I believe the poppets need a higher pressure to start than to run. So if his engine is starting fine, then likely not a fuel delivery problem. Otherwise it would not even start.

Of course, it could be below spec., but not the problem to his question.

I have had my truck for 18 years. I have replaced the FP IDK maybe 7 or 8 times. Anything under 60 PSI, and the truck gets hard ti start but only sometimes. Also there is a lack of power at WOT at high RPMs as the engine is starving for fuel. If you hook up a pressure gauge, you can see the changes in pressure as the engine RPMs go up, the fuel pressure goes up. This happens as the fuel pressure regulator sees more vacuum. Before starting the engine, when you turn the key on, the ECM cycles the fuel pump for 2 seconds I think. This builds fuel pressure to max ( 60 min, 61, or 62 PSI ) this gives enough pressure to force fuel through the spider, and poppet valves.

 

[stutaeng]

Ok, I understand. I've never seen over 60 psi in either my 4.3 Vortec or my 5.7 Vortec. More around 58 psi.

I did have a crank-no-start on the 4.3 that I never figured out, but only happened on damp or raining conditions. Pretty sure I ruled it to distributor. I just pulled that engine because it also had low oil pressure. So I didn't want to spend the money on a new distributor. I never suspected the fuel pump. I did have a low leak down, so could have been a FPR. Injectors, surprisingly checked ok, LOL.

On the 5.7 is where I learned how to diagnose the P0174. Messed around for about a year checking sensors with DVOM. Changed all 4 O2 sensors. I also had an intermittent sensor code about O2, but that was a result of the P1074 code


Finally got a basic scanner with live data and within an hour I had 100% percent certainty it was injectors. Put a new set and problem solved.

A $30 Fuel pressure gauge probably has saved me about 3 or 4 fuel pumps on those 2 trucks if I did the parts cannon approach.

Fuel pumps have got to be the most wrongly changed part on these trucks, after plugs and wires and cap and rotor.

I'm positive we can diagnose OP's 0174 code by simply looking at fuel trims...no need to start changing part. At least not yet.

 

[stutaeng]

Kenny, you are right though on spec. fuel pressure.

Those service manual PDFs are now showing up correctly and they specify 60-66 psi...

My bad.

 

[kennythewelder]

Kenny, you are right though on spec. fuel pressure.

Those service manual PDFs are now showing up correctly and they specify 60-66 psi...

My bad.

No problem. I have never seen 66 PSI, but I know it is max. Another clue to low fuel pressure, is an O2 sensor code. To much O2 and not enough fuel. Mostly at WOT, or at higher RPMs. For an old man ( almost 62 years old) I have a lead foot. My truck has some performance mods., and I like to drive hard and fast. My truck is at about 325 HP and runs a 15 second 1/4 mile. So not super fast, but better than stock by far. So I notice a lack of fuel pressure when it happens, or better yet, when the truck is starving for fuel. If someone drives easy, slowly, ECT they may not notice this as quick as I do. My driving habits demand more fuel than your average driver.

 

[mark hilburn]

get a new spider assembly .