York

Hi everyone. This is my first post here.

I have a couple Chevy's, but the subject of this post is a 2000 Blazer (S10 variant) with the 4.3lt engine in it.

It's developed an interesting issue and I thought I'd get a collective opinion on it.

I'm not its designated driver, just the designated fixer. I'd received complaints of loss of power "cutting out" stalling, etc, but whenever I drove it, the vehicle had plenty of power and drove perfectly. Further quizzing on when does it do it, hot? cold? initial start up? etc was met with, uhh, dunno. Gotta love that.

Since it always drove perfectly with me, and it had reached 120K I thought a tuneup was more than in order considering it had original plug wires, cap, and rotor. Plugs had been replaced with an OEM variant at 100K. So I did a tune up evolving replacing the Plug wires, Cap, Rotor, and fuel filter. Still the driver reported occasional loss of power and cutting out.

When? Dunno. Hot cold warm CAN YOU PLEASE WORK WITH ME A LITTLE HEAR? dunno. sigh. After a bit I did seem to work out that it appeared to happen shortly after start up, usually after it was hot but not always. So I tried to simulate that and finally got it to act up.

What it is doing. I haven't check it cold, but, after driving a bit, if you pull off, shut off the engine, wait 3-5 min, restart, anything above about 1/4 throttle with make it sputter and bog down almost to the point of backfiring. This will carry on for about 20 seconds/100 yards or so then clear up. Backing off the throttle to about 1/4 throttle for the 20 seconds/100 yards works too. Or, just sitting and letting it idle for about 20-30 seconds before you take off will work as well.

After that it has plenty of power, runs perfect.

It does and always has started up on first tickover, very fast and easy starting engine, never had any issues there.

So no starting problems, no performance problems after the initial short period. The key here though is you can be driving alone running perfect, pull off, shut off, wait 3-5 min, and initially you won't be able to go above 1/4 throttle or so until you've covered a few hundred feet or about 20 seconds.

I thought at first perhaps it was a leaky injector bleeding down the pressure and flooding it with fuel, but there is no smoke out the tailpipe upon start up like I would expect if it was flooded enough to cause it to stutter for so long, and it has no problems starting as one would expect if pressure had bleed down, also it sounds as if it's almost ready to start backfiring which usually means lean.

My guess therefore is that it has pressure, but not volume. A failed regulator perhaps, or a dying pump that can archive pressure but not volume is my guess.

Has anyone ever experienced this issue before?

I don't have a pressure gauge and it will probably be Tue before I can get one. At that time I will be able to run some tests, check out the regulator etc.

In the meanwhile, thoughts? Opinions? On base? Way off base? Gee this guys an idiot?

York

Hi Gary, thanks for the warm welcome.

I'm back with pressures! Sorry it took so long, it took me a bit to get a gauge setup, and then a bit longer for the vehicle to stop moving long enough for me to snag it into my troubleshooting lair.

Also, as per your earlier inquiry, no, I'm afraid I didn't put AC delco cap and rotor on it. It was late at night (8:55pm if I recall right) and the only place that was still open was an O'Reillys autoparts. I did get the better of what they had though. That's a very expensive Cap and rotor, I think I spent $50+ on them. (I'm used to my old Saab C900's, $15 will get you an OEM cap and rotor)

I don't think they were the problem though, as the problem existed both before and after replacing the cap, rotor, and wires. Don't ya just love that? But it needed them, they were the original ones I belive.

Getting to the point though, pressure test results.

Ignition switched on, engine off. 60 PSI. Pressure drops to zero after the pump stops it's 2 second primeing session.

Engine running. 54 PSI. Wobbly. Apply slight throttle, gauge needle stabilizes rock solid at 55 PSI. Let off throttle back to idle once again vabrating gauge neeedle at 54 PSI. Sbut engine off, pressure drops to zero.

I had the gauge on the port at the back of the engine. I assume this is the only port and I didn't have it on the return line, they wouldn't put a pressure port on a return line would they?

Also, I'm a bit confused on what kind of system I have. The vehicle is a 2000, so I'm assuming CMFI or CSEFI, but it doesn't look like any of the illistrations in the book, and the description in the book isn't very clear on how to determine what is which.

So attached for your viewing pleasure...





Any idea which system it is?

And the problem. Does this system have a fuel pump/line check valve/anti flowback?

Or would it be the fuel pressure regulator? It wouldn't be able to achieve and maintain 60 PSI if the fuel pressure regulator was knackered would it?

Cheers!

Thanks for any help or ideas. (:
York

drperry

The pressure seems good...

But it should definitely hold the pressure for longer than 2 seconds after the engine is shut off...

It could be the pump is slowly on its way out, as well... Especially if it's never been done.

But definitely something wrong in the fuel system...

Hopefully someone with a more specific idea chimes in soon!

I have to track down random hesitation in mine... Which can apparently be a bad distributor drive gear! lol

chevyboy572

ok.. heres my 2 cents.. spend them as you will, I am not ruling out fuel or ignition, but im trying to broaden the diagnosis, it can also be an intemident tps fault. not enough to set the SES light, but enough to cause a cough.

Now if it isnt that, fuel, a weaker pump will definatly cause this. it will give you what you need and then go, "oh god!" then keep up with you again. and as to the pressure bleeding down, it can still be an injector or the Pressure regulator. other than that, im not ssure where else to look.. hmmm. let me think an ill chime in again..

oh wait! Last oil change? when? what does the oil smell like? smell like gas more than it should? Any leaks around the manifold?
Eric

Turn this car around

Did you blip the throttle wide and record the psi? If so what is it.

drperry

The fuel pressure should not change very much.

The 5.3L V8 has the same pressure readings as the 4.3

It should be reading 60PSI or so before you start it, and drop to 55ish, I think, once it's running.

Turn this car around

I do believe if you check the spec. For it it will tell you wide open throttle psi is 66psi .Idle 55 to 60 you just might want to check it. And I'am talking 4.3 here Blazer............

drperry

I did say "should" not definitely, lol

But yeah, 55 or higher at idle... But it does have to be at 60PSI to start, IIRC.

far2grumpy

Don't know if the following is anywhere close but is extract from SB covering several 4.3, 5.0 and 5.7 "rough-idle" engines.

This is extract only ... I can send the whole deal if you PM an address.

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) #00-06-04-003B - (Jan 30, 2003

Some customers may comment on rough idle after start-up, especially if the vehicle has sat overnight. These symptoms may be intermittent. The Service Engine Soon (SES) light may also be illuminated.

Current misfire or history misfire codes may be detected with the Tech 2 scan tool.

Cause

A deposit build-up on the CSFI poppet valve ball and/or seat may cause the poppet ball to stick open or closed. In either case, the specific cylinder will be mis-fueled, resulting in a cylinder mis -fire condition.

Correction

A new injector unsticking and cleaning process has proven to be effective in restoring poppet valves to an "as new" condition. CSFI injector replacement should NOT be considered as a correction for this
customer concern.

Check the vehicle history to determine if the vehicle is returning for a second fuel system repair for this condition. If the fuel system has been repaired for this condition previously, then inform the customer that an alternate fix is available. A new MFI fuel system has been developed that will back service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a unit. Refer to Central SFI to MFI Conversion instructions in this bulletin.

Notice

Individual CSFI injectors can not be replaced with MFI injectors. The entire CSFI fuel meter body will need to be replaced. The bracket used to retain the injectors in the fuel meter body is different between the CSFI and MFI unit. The unit may not seal if you mix injectors. Severe engine damage could result.

Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with an MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.

Turn this car around

Have you tried any mechanic in the can solutions.I would use some 44K or some sea foam to see if this helps you first.As a one time check you don't want to run it all the time.