4.3l v6 strange miss problems

I have a 2001 chevy s10 with the 4.3l v6, Problems started about 2 months ago. Hot start after 10 minute shut down, engine does a millisecond shut down then drives ok for the rest of the trip. several days later, it throws a p0102 code twice and sets off the SES light. 2nd or third drive it clears itself. but the p0102, 01/01 wont clear, and the strange millisecond stall still occurs randomly. Have been checking various items, like fuel pressure, obdII data, etc. Cleaned MAF, but dropped it, so had to buy a new one. It is reading about 0.6#/min at idle, and as high as 12, when acellerating through gears. Also noted that starts were taking about 3 seconds, normally, they take about 1 second. Had this problem 4 years ago, and solved it with a a new fuel pump. Problem still was occurring. Came to wrong conclusion that the fuel pressure regulator was causing the problem, so replaced it with a midprice new one. First attempt to check it, the fuel pressure dropped from 57 psi to below 40psi in seconds. Didn't like that result so, put fuel pressure gauge on the output of the inline fuel filter to see if the pump check valve was leaking. Result was the pump jumped up to 90psi, bled down to 60 psi, then held between 60 and 40 psi for about 30 minutes. Concluded that the first leak down was not back through the fuel pump. Checked the bleed down at the rail schrader valve again, and the bleed down was a little better but drops from 57 to 30psi in <5 minutes. some where in here checked fuel trims and they were way out of wack, ltft > 24% both banks, stft bouncing around all positive like the closed loop system was trying to feed more fuel to the engine. On next short--3mile test run-- the fuel trims have come down ltft about 10% and stft about 0. But it threw another code P0131 as well as the original P0102 code.

I'm betting that I need to replace the new fuel pressure regulator, since it is about 5 psi low and may be slightly leaking. I'm not sure if the P0131 code is a result of the original problems and "may" go away if I solve the first problems or if it is the main culprit in causing all the issues.

I'm retired now so don't do a lot of driving--120,000 miles on the truck.

Would some one like to make a few recomendations? I have just a OBDII reader, no scope analyzer type equipment. I do have typical test equipment like VOM, clamp on amp meter, portable DSO— not specialized for autos. Lots of hand tools etc.

Regards,

Vic Jordan


I fortgot to add that driving with the OBDII reader, it was forced into a reset several times, while this has never happened in 5 years, previously--made me think that some sort of electrical intermittent is happening. Had to replace the radiator about a year ago, since then have added 50/50 mix twice about 2 qts total--haven't checked for a head gasket leak, but don't think that is a problem. Don't see any white smoke or any smoke at all.

 

Before you do anything else, you need to get solid fuel pressure results. Read the sticky and report both intial pressures and then leakdowns at 10 min (4 numbers). If you are still having problems after we straighten out your fuel pressures then we can move on to other areas.

George

 

Hi George,

l was hoping you would reply to me after reading the discussion where you were helping someone while in a hospital waiting room. So far I’m too new to this web site to be able to recognize what a sticky is! But I do have some numbers on the bleed down of fuel pressure which I will include below. I have also done some testing on linearity of the TPS—it’s good from 0 to 100, MAP reads 24.8 inches engine off— altitude is 5260 msl, it reads idle vacuum of about. 8 inches.

coditions: engine off, key off, fuel pump relay removed contacts shorted for 3 seconds.

pressure gauge connected to output side of new fuel filter with hose clamps rubber fuel line tubing. Just testing the pump check valve.

pressure jumps up to 90 psi guage.

time Fuel pressure

11:10:15. 60 psi

11:14:15. 57

11:18:15. 55

11:24:15. 50

11:31:15. 46

11:40:15. 42

11:46:15. 40

conditions: fuel rail testing closed loop fuel system, key off, engine off, relay contacts shorted by hand.

max pressure. 57 psi guage

time. Pressure

12:05:45. 57 psi

12:06:45. 42 psi

12:07:45. 38

12:09:15. 34

12:12:00. 30

I can do these tests again if your sticky note has some other test.

regards,


Vic Jordan

 

Here is the fuel pressure sticky:

https://blazerforum.com/forum/2nd-ge...eakdown-88305/

The main take away is to record fuel pressure at key on and then ten minutes later to monitor leak down first at the schrader and then after the fuel filter. That helps us figure out if you have a problem and if so is it in the intake plenum or back at the tank (or both). You want to see 60-66 psi at key on at the fuel rail and hold at least 55 after ten min and 73-108 at key on at the fuel filter and again hold at least 55 after ten min. What brand fuel pump is this? How about the injectors and regulator?

George

 

Fuel pump was installed 3.5 years ago, Delphi new, with life time guaranty. Fuel spider is original, looked dirty when I replaced the fp regulator. I should have taken a picture but didn’t. Was wondering how the shut off solenoids work and if their is some way of putting an O’scope on the pins to check if the pcm has drive problems.

from the data I have, the closed loop fuel pressure hardly holds above your sticky data for a minute. So I’m betting I need to get a better fp regulator. Is it possible that the intake fuel seals into the spider are leaking and are replaceable? They are really hard to pull out and shift away from the spider in my model S10.

vic

 

Yes, it looks like you are leaking at the engine. That can be the regulator, the injectors or the hoses in the plenum. Usually if its the regulator or hoses/tubes the intake is clean and shiny under the leak unless the regulator is leaking into the return line. If its the injector(s) then you should have some wonky plugs and/or smell gas in the oil. One way to test the injectors is a balance test where a fixed set of pulses is applied to each injector in turn after charging the rail and watching the pressure drop, then comparing how uniform the results are. This can be dome with an injector pulse box or a capable scanner.

George

 

George,

i have a borscope, I think I can put it down the butterfly valve, then run the pump by hand to see if I can see a leak. I won’t be able to see it at the injector tube outputs. I’ve tried the smell test for fuel no luck yet. I’m of the general opinion that if I have to go back into the plenum that it would be smart to replace the spider. I’d rather spend money on a 2001 s10 than to spend 50k on a new truck, then not be able to repair it myself. I had read about the idea to watch for clean leak spots, but I didn’t see any. I’ll pull the plugs to check for carbon or wet plugs before I buy the new fp regulator or spider.


thanks for the help,

vic

 

AC Delco spiders and regulators are available again so hopefully that provides reliability for the repair.

George

 

Hi George,

I spent today in a waiting room while my wife got a total knee replacement. Funny how Life seems to repeat itself.

 

Good luck for your wife's surgery. Gettin' old ain't for sissies.

George