Hello to all.
I have a 95 4x4 V6 (4.3 i think) 4 door Blazer and up until today this was my most reliable vehicle (for winter use) I store it away in summer and come around this time of the year I un-wrap her and try to fire the beast up, however this weekend did not go to well.

I have searched but not really found anything that explains the situation.

The engine cranks and cranks, but does not start, I have done the following:

1) Checked pump (will come and run for 2-3 secs when key turned (but not started))
2) When trying to start the engine there is exhaust pressure when I place my hand over the tail pipe (so getting air)
3) Changed fuel filter
4) Checked spark (took plug out, grounded it and tried to start, got a good spark.
5) Put fuel pressure guage on and that is where the confusion starts.

When key is in position II (When lights on dash come on) the pump starts and runs for a few seconds, the pressure goes to around 60psi...great, but then the pressure drops to around 15-20psi. When I try to start the engine (just keeps turning over) the fuel pressure stays around 20 psi. I turn the key off, wait for about 10 seconds and then the same thing happens, gets initial pressure around 60psi and then I think when the fuel pump stops running it drops down to 20psi again, and stays there when I try to start.

Questions...

1) Is this normal for the fuel pressure to drop down after the pump stops working? I would have thought the fuel would have been a closed system so no loss in pressure?
2) What to try next? Could it be the fuel pressure regulator?

I'm hoping its not the pump on the way out, but if it is, then so be it.

Any help would be appreciated.

Thanks,
Ryan.

 

Turn ON the ignition leaving the engine OFF, the fuel pressure should be 415-455 kPa (60-66 psi) when the pump is running. This pressure is controlled by a spring pressure within the regulator assembly.

The fuel pressure that continues to fall is caused by one of the following items:

- The in-tank modular fuel sender is not holding pressure.

- The fuel pressure regulator valve is leaking.

- A Central SFI injector is leaking.

- Fuel line is leaking.

If the fuel pressure is less than 379 kPa (55 psi) at idle, it falls into the following 3 areas:

- The pressure is regulated but less than 379 kPa (55 psi).The amount of fuel reaching the injector is sufficient, but the pressure is too low. The system will run lean, hard starting cold, no start, overall poor performance, and may set a DTC. Refer to Engine Cranks but Does Not Run

- A restricted flow causing pressure drop -- Normally, a vehicle with a fuel pressure of less than 300 kPa (44 psi) at idle is inoperable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop running as the pressure begins to drop rapidly. This is most likely caused by a restricted fuel line or plugged filter.

- A leaking or contaminated pressure regulator valve or seat interface may not allow the regulated pressure to be achieved.

Notice: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel system.

Restricting the fuel return line allows the fuel pressure to build above regulated pressure. With the fuel pump commanded ON, the fuel pressure should rise above 455 kPa (66 psi), as the valve in the return line is partially closed.

When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel pressure regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on the barometric pressure; however, the pressure at idle should be less indicating the pressure regulator control.

 

Chevy Lover, thanks for the quick and very detailed responce.

I think it is time to remove the inlet plenum and see if there is something leaking internally. Hopefully it is noticeable inside.

I have not been able to start the truck, and I do not want to start using ether (or some other starter fluid) in the inlet until I can at least look inside for excess fuel, I dont want to cause anymore damage than necessary.

Again thanks for the help in thi issue, I will update my findings later.

Ryan.

 

Ok, another update..

So I took off the upper intake and there was some signs of fuel on the left hand side, but I think one of the poppet valves was loose, so that explains that.
To confirm the falling fuel pressure I restricted the return fuel line and the pressure now doesn't even go over 20psi? No leaks anywhere, inside the fuel injectors, leads, filters or joints, I'm thinking that it must be either the fuel pump (however this runs for 2-3 seconds) or the sending unit. I am thinking the sending unit but didnt want to rip out the tank before at least someone agrees with me on this.

Would it be best to replace both pump and sending unit while I am in there?

I dont think its the regulator valve as no fuel is leaking even if I clamp off the return.

Can the pump still run but not produce a high fuel pressure? Is this the failure mode?

Any help would be appreciated.

Thanks,
Ryan.

 

Yes, the fuel pump can run and not produce the required pressure. I believe you have a pump problem. It sounds like you get your 60psi initial pressure, but then it drops to 20psi. The engine won't run on 20psi.
The fuel pump is in a module, which contains the pump, the pulsator and the level sensor.
When you get it out, have a look to see if the pulsator is loose. It's possible to have a pressure drop if it is.

I'm looking for a pic...

[IMG]local://upfiles/2910/7062C2500EA44E319B20112C6D9D7888.gif[/IMG]

 

Ok, So I replaced the fuel pump in the tank and checked to make sure I got the right pressure before I fully installed the tank and what a reflief I now have a full ~60psi and it holds! So that was the good news, now let me tell you about my past few days....which had some bad news associated with it.

I removed the upper plenum to again check all the spider assembly for new leaks as I now have the correct pressure and noticed the fuel return line was leaking a little bit from the spider assembly, I thought no big deal, I will remove the rectangular retaining clip and replace the o-rings, in my excitment about thinking it could almost be running due to the fact that I replaced the fuel pump I inadvertinly dropped the rectangular clip down the upper left air passage to the cylinder #$$#%^#%^ even with my 2 foot long claw tool I could not get the clip out, it was nowhere to be seen. So this meant the whole lower part of the intake had to come off.

So after removing everything in sight and the distributor (which I marked correcly) I finally got to see a glimpse of the clip, teatering on the edge of the valve. I was able to grab it with my claw tool and a sigh of releif was felt. While I was in there I also removed the valve covers and degreased everything, replaced the PCV grometts, replaced all the gaskets and my, it does look clean.
So put everything back together and got round to replacing the distributor, as I said before I was very careful to mark everything and made sure I did not turn the engine.

So i was puzzled to the fact that my paint lines would not line up. I placed the distributor back into the hole with the new round seal, lined up the spirol pin with the base of the distributor and put the clamp back over, but when I tried to line the black round metal disc to the mark on the ditributor body it was off by about 20deg.

I kept the spirol pin located with the base and rotated 1 tooth, this seemed to line up perfectly yet it would not seat all the way down when I align everything. It seems the spade shapped piece at the very end of the shaft can only be inserted 180 apart? Panic starts to set in....

I tried not lining up the spirol pin with the distributor body, every mark then aligned, but the distrubtor body was rotated by 20 deg clockwise, enough that when I tried to put the upper intake back on the plug wires were interfering with the intake.....ahhhh...I knew I should have taken photos at the start of the job...

So I put it all abck together with the 20 deg offset so the lines did not line up internally to to the distributor rotor and tried to start it gently, but nothing, just a few missfires. It also seems to want to start but when I think it has ignited the engine stops rotating with a thud?

So questions:

1) Does the spirol pin and ditributor have to align?
2) How can I check to make sure that the timing is in fact correct. I know there is a sequence of removing #1 spark and checking for pressure, then I get lost, I see on the main crank damper there are two slots and a mark onthe actual engine block, but do I align these to find the correct position for cylinder 1?
3) Is there any other way of installing the distributor to get around the spirol pin assembly?
4) Why does it not line back up again, maybe it was not correctly located to start off with?

Please help, I am so close in getting this thing to run, just a few more days and I should be there.

Also I noticed that when trying to crank the enigne seems very slow in turning over. I think it rotates about once every second, is this two slow? Do you think the starter is on its way out?

Thanks, I appreciate any feedback to help solve this problem.

Ryan.

 

See the post "how do I check the timing" USMaverick101
I wrote a fairly detailed post on finding #1

The slot you see in the bottom of the hole below the distributor is the oil pump drive and sometimes it moves a little when the distributor is removed. You can use a long flat blade screwdriver to turn it to line it up with the distributor, or, bring your timing back to #1 as posted, get your distributor installed to the lowest point it will go down (and you figure if it went down the last 1/4" that it would line up), then hold a little downward pressure on the distributor, so it doesn't pop up, and have someone crank the engine til the distributor drops into position (as the slot lines up with the oil pump slot)

I hope this is clear...if not , post to let us know and I'll try to explain more clearly.


Isn't learning fun....lol

 

Chevy Lover, you were spot on about the oil pump drive, I lined up all my original marks and rotated the engine using a socket wrench on the crank and pushed on the distributor, not an easy task I may add by a single person, anyway it dropped right in and I now have the original timing and distributor placement back and the paint marks line up exactly. Very Happy.

When I tried to start it still won't start, however there is what seems like an internal backfire coming from somewhere within the engine?

So far all that I have done (that seems to have improved some what from the initial problem) is to replace the fuel pump and verified ~60psi. I have checked all the spider assembly and verified that nothing leaks internally. There is air going into the system and pressure in the exhaust when I crank.

I am getting a new spider system (should arrive this week) to see if the poppet valves are working correctly.

It still seems to turn slowly, I even tried to jump start using the battery from an 04 explorer (wifes car) but still does not seem to turn over quick.

Any ideas on what to try next?

I have replced all the distributor compoenents including cap, body, leads and spark plugs, and I do have a good spark (verified on #1)

Could it be flooded? Do I need to crank it a few times with the plugs out?

We're getting closer I can feel it

 

Are you sure you are on the compression stroke.
Remember that your timing marks on the crankshaft pully will line up twice, once on compression and once on exhaust stroke.
If you are experiencing internal backfiring, your distributor might be out 180 degrees. That's why I recommended that you use a helper so you can feel the compression stroke with your finger.

 

Let me just say that seeing as how you rotated the engine after installing the distributor 1 tooth off, chances are your original marks on the distributor mean nothing now... You really have to go through finding TDC on cylinder #1 then setting up the distributor so the rotor is lined up on the #1 post.