Hard Starting - Fuel Pressure Concepts
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Hard Starting - Fuel Pressure Concepts - 2/28/2007 8:32:22 PM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
Status: offline
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Hello All...
2000 4dr 4wd LS 4.3l V6
I've had the truck leave me stranded a couple of times recently. When it's cold and he vehicle has had a chance to sit for more than just a couple of hours, it'll turn over (and turn over and turn over)...but not start. After a couple of tries starting, this seems to result in a flooded condition. I say this because the oil smells strongly of gas...and...because it just acts flooded. When it's warmer out, the truck starts better...but, still turns over more times than "normal" before it starts. It does this whether I "prime" the fuel system or not. By "prime", I mean turning the key part way first (for a few seconds) and then turning it the rest of the way to start to allow the fuel system to pressurize prior to starting.
I've done some online reading (a significant portion of it here), and found that these are common symptoms of a bad fuel pump check valve (leaking), fuel pressure regulator (leaking), or bad fuel injectors (leaking).
I tested fuel pressure at the fuel rail and found that I have about 60psi fuel pressure immediately after I turn the key...just letting the fuel pump cycle (no start). Within less than one minute, fuel pressure falls to zero (yes, that fast). If I start the vehicle, fuel pressure stabilizes around 55psi at the fuel rail (running). All this really tells me is that I cannot maintain standing fuel pressure...because of a leak somewhere.
I have looked inside the TB past the throttle plate, and do not see raw fuel (before and after fuel pump cycle). I do, however, smell it inside the TB after fuel pump cycle. While I cannot eliminate the possibility of leaking fuel injectors...this set of cirsumstances leads me to lean strongly toward a leasking FPR.
I had the fuel pump replaced about 6 months ago. So, while POSSIBLE...I'm thinking that a fuel pump problem is unlikely.
So, here are my questions...
1) Am I on the right track to be targeting the FPR and fuel injectors?
2) If so, how do I identify the single problem component without removing the upper intake plenum for individual component inspection?
3) If not, where should I be looking?
Also, I see information on how to go about changing the FPR for "CPI" systems all over. I think that means "central port injection". I've been told that my injection system is a "multi-port" fuel injection system.
Is this true? Is FPR replacement the same for each? If they are different...what is the correct procedure for replacing the FPR...assuming that is the problem.
Thanks in advance for the direction!!
Icarus76
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RE: Hard Starting - Fuel Pressure Concepts - 2/28/2007 10:48:54 PM
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Kordog
Posts: 403
Joined: 10/22/2006
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Yes your truck has the multi port not the cpi FI. The only way you will see what is leaking is to take the upper intake off. Then put the fuel lines back on, and prime the system. The FPR is of the same design as the old CPI units. I have not replaced one yet, but it should be really easy once you are under the upper intake. Pulling the upper intake is pretty easy, and the gaskets are even reusable, but I would replace them since they are pretty cheap. Korey
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Korey
2000 Blazer LT, 30X9.5x15 Dueler AT, Cold air intake, Magnaflow exhaust.
ASE Master Auto Tech.
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RE: Hard Starting - Fuel Pressure Concepts - 3/1/2007 10:23:21 AM
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swartlkk
Posts: 14473
Joined: 5/1/2005
From: Waterloo, NY
Status: offline
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Like Kordog stated, you really need to open it up, reinstall the fuel lines and repressurize the system to find the leak. It is quite possible that it is simply an o-ring on an injector.
The stock SCFI system has an injector and a poppet nozzle. If the injector is leaking, then so will the poppet nozzle until the pressure drops to below ~45psi after which it may still weep (due to their notorious tendancy for tarnish buildup on the seat), but not at the same rate. If the pressure bleeds off from 60psi at a steady rate, I'm thinking you have either an injector oring problem, a leaking FPR or the check valve in the fuel tank is spent.
As far as buying new injectors... Well, it is MUCH more economical to purchase just the FPR if that is the only problem. But instead of buying new injectors/poppet nozzles, the updated MFI spider that is a direct replacement for the original setup is a much better option If you have to replace the FPR and 2 injectors, you just paid for a new MFI setup from the dealership, but if you only have to replace some o-rings, well... The entire MFI spider sells for $160 +s&h at GMPartsDirect.com and is available under PN 12568332, but the s&h is steep and shipping is slow in my experience with them. It should be available from the dealership for around $200-250, but could be as high as the $300 list noted on GMPD.com.
And I wasn't ignoring this post. I thought that Kordog had given the necessary suggestions and was waiting for a followup as to your findings.
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Hard Starting - Fuel Pressure Concepts - 3/1/2007 11:08:59 AM
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swartlkk
Posts: 14473
Joined: 5/1/2005
From: Waterloo, NY
Status: offline
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I didn't see it as sarcasm either. No worries!
Where in CNY are you located?
*EDIT* - Now with the removal of the plenum, you will need to remove the fuel lines. This can be a pain in the *** with the distributor in. I was able to flex mine out of the way enough to get the upper plenum off, but I will NOT do that again nor would I recommend it. I had a really fun time attempting to get the lines back into the SCFI body.
Best advice that I can give is to use a stubby wrench to disconnect the fuel lines. If you don't have enough room, then you may have to mark and remove the distributor and make darn sure that you don't bump the starter at any point before you drop it back in.
< Message edited by swartlkk -- 3/1/2007 11:19:56 AM >
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Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Hard Starting - Fuel Pressure Concepts - 3/1/2007 1:04:38 PM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
Status: offline
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Hmm...
According to the chevy dealership...I cannot get a "spider" for my vehicle. GMPD verifies this. PN 12568332 is not listed under my vehicle in GMPD's catalogue...only the sigle FIs (PN 17091432). I guess I'll just grab a couple injectors...and hope that I don't need them.
Icarus
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RE: Hard Starting - Fuel Pressure Concepts - 3/1/2007 1:25:08 PM
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swartlkk
Posts: 14473
Joined: 5/1/2005
From: Waterloo, NY
Status: offline
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This is wrong and is because they do not show it for your application is even more wrong. It is a direct fitment and what is used on the 2001 or 2002+ engines. The PN is correct. It won't show up under GMPD.com's catalogue, but I assure you it is correct. I have a TSB referencing this replacement spider for the fix for varnished poppet nozzles that resist cleaning.
quote:
Fuel System - MIL ON/Rough Idle on Start-Up
File In Section: 06 - Engine/Propulsion
System Bulletin No.: 00-06-04-003B
Date: February, 2003
TECHNICAL Subject:
Rough Idle After Start, And/Or A Service Engine Soon (SES) Light (Unstick And Clean Central Sequential Fuel Injection (CSFI) Poppet Valves or Convert to MFI)
< Message edited by swartlkk -- 3/1/2007 1:26:33 PM >
_____________________________
Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Hard Starting - Fuel Pressure Concepts - 3/1/2007 1:53:58 PM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
Status: offline
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Maybe I'm confused...
Does this PN 12568332 include fuel injectors, or is it just the spider body?
If it all inclusive, I may still be interested. I understand it requires the use of an additional bracket (PN 88894355).
Does it come with seals and retainers for the FIs? If not, are the seals and retainers the same as in kit PN 17113205?
Icarus
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RE: Hard Starting - Fuel Pressure Concepts - 3/1/2007 2:46:32 PM
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swartlkk
Posts: 14473
Joined: 5/1/2005
From: Waterloo, NY
Status: offline
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PN 12568332 is an entire injection spider kit. It includes the injectors, metering body, the FPR, retaining plate, and all internal orings. If you did need to replace any of the orings, they are the same as those used in the current metering body.
The bracket is exactly the same as the one in your engine.
_____________________________
Kyle-
2004 Rainier
1970 Chevelle - Resto
1974 K5 Blazer - Resto
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RE: Hard Starting - Fuel Pressure Concepts - 3/3/2007 5:37:28 PM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
Status: offline
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I did end up finding the MFI spider...and buying one.
When I got into the upper intake area I found signs that several of the fuel injector o-rings ~had been~ leaking (moistness, gumminess, tarnish). But, for some reason, they did not visibly leak when I had everything opened up. I pulled each fuel injector out of its hole, while having someone cycle the fuel pump for me (once for each fuel injector). None of the poppet nozzles appeared to be leaking...nor did the FPR.
As I said before, I just had the fuel pump replaced about 6 months ago. So, I started thinking about what else could be going on. I don't know enough about the metering body, as a system, to be sure. But, I thought that fuel pressure could be bleeding to the return line when it shouldn't be. It would have been nice to have had caps for the fuel lines (before the fuel rail) to isolate and test before the metering body...but, no gots.
Anyway, partly because I was there, with everything open (and the MFI spider was only a couple hundred dollars) I did install the MFI spider. Before putting the upper intake plenum back on, I did replace the connections, pressurize the fuel lines, and test.
What I found was that fuel pressure was still bleeding off, as steadily as before, but much more slowly than before. Now, it fades from about 60 psi to about 20 psi in one minute...and then hovers around 20 psi for about 2-3 minutes before falling the rest of the way to zero psi. There wasn't much else I could do in the area I was working in. So, I put everythng back together and ran the vehcile.
Some things are better...but, the truck's still not right. The vehicle acclerates more smoothly and quickly...and that's about all I earned for a days work. It still idles roughly...and starts like crap. I still need (or at least want) to change the plugs. I haven't checked them yet (I know I should have)...but, I estimate the excess fuel they were getting gummed them up. I suppose that might help the idle...not sure.
It's dissapointing to think that I could be having problems because of the fuel pump check valve 6 months after having it put in...but, I'm thinking that that's my next target.
Any feedback would be appreciated!
Icarus
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RE: Hard Starting - Fuel Pressure Concepts - 3/5/2007 11:28:50 AM
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Icarus76
Posts: 45
Joined: 8/22/2006
From: Central New York
Status: offline
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I had a look at a friends factory service manual for his '95 (I do not have one for my vehicle). I imagined that some things may be similar enough to at least give me an idea of other things to be looking for, or at.
In the troubleshooting section for hard cold weather starting, there is some information on how the fuel pump is wired from (or through) the oil pressure sensor. The manual outlines that when the fuel pump relay fails (or becomes intermittant), a fuel pump start signal will come from the oil pressure sensor BUT only when proper oil pressure is achieved. Apparently, this was done to prevent the fuel pump relay from being a single point failure. This set of circumstances explains the difficulty in cold weather, as proper oil pressure is more difficult and time consuming to achieve.
Could this be the problem in my vehicle? Is this configuration still used in 2000?
If this is a problem for me, or anyone else, I'm suprised it would go undetected. I would think the ECM would be aware that the fuel pump relay was no longer generating the start signal and post a fault.
Thoughts?
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RE: Hard Starting - Fuel Pressure Concepts - 
...I assume I must be on the right track to be looking at the FPR and injectors for leaks. 
