Jump to content

Need Csfi Help. Please!

Old Frog

By Old Frog
in Ask A GM Technician

Recommended Posts

Old Frog Enthusiast

Old Frog

Posted
Posted

1997 4.3, CSFI fuel system. 155K miles, Stock components/no mods.

 

Background: Intermittent no start problem fuel related which appeared to be a result of low fuel system pressure. No visible leaks. Fuel filter & pump replaced professionally. About 1 year & 40K miles later, problem reappears.

 

Because for the cost, I am doing the work myself. No CELs displayed. System Pressure low. About 50 PSI. Fuel pump relay & electrical system components all appear fine. Key On, Engine Off, pump cycles & pressure builds. Engine will start with a shot of starting fluid & continue to run & drive fine after that but will not restart without another shot of starting fluid. No visible kinks or restrictions in the fuel lines.

 

Fuel pump & filter replaced again. While I am at it, new plugs wires, cap, etc. installed. Still no start & pressure still @ around 50 PSI but will start fluid & continue to run. Return fuel line restricting valve test done (pressure to high high 60's (I did not push it higher)) indicating faulty fuel pressure regulator.

 

New fuel pressure regulator w/ screen & o-rings installed. Pressure now a biot higher, to 52 PSI but Engine still will not start cold, will start on fluid, run fine restart when hot. With engine running, pressure gage readings range in the mid 50's to low 60's. When the engine turns off, the system reads about 55 PSI. System holds pressure in the mid 50's for some time. Overnight, the pressure falls to 0. Key on cycling brings pressure to 52 but fluid needed to start.

 

I am starting to get POed by this time. Any suggestions on how to fix (other than a bit of C-4) would sure be appreciated.

Old Frog Enthusiast

Old Frog

Posted
  • Author
Posted

Anyone?

 

Now I am wondering if it is a sensor problem @ cold start or perhaps the CSFI to MFI replacement tsb issue. From what I can tell, the symptoms do not match completely.

Jeremy WI Enthusiast

Jeremy WI

Posted
Posted
Anyone?

 

Now I am wondering if it is a sensor problem @ cold start or perhaps the CSFI to MFI replacement tsb issue. From what I can tell, the symptoms do not match completely.

 

Was the fuel pulse dampener replaced when the fuel pump was? I was told the 96's had a bad problem with them being faulty and leaking

Old Frog Enthusiast

Old Frog

Posted
  • Author
Posted

"fuel pulse dampener" This is a new one to me. I have not heard the term before. I replaced the pump. Pressure still low so I ran the return line restriction test, pump produced up to 70 PSI. My impression was that it would go higher except the manual I am going by cautioned about damged if pushed too high. This lead me to replace the fuel pressure regulator under the upper intake manifold. In doing this, the Pressure when from about 48 to 52 PSI. Still low.

 

Where is the fule pusle dampener? Thanks.

Jeremy WI Enthusiast

Jeremy WI

Posted
Posted

Just above the fuel pump, looks a lot like a miniature brake fluid reservoir on my 96. I am sure some replaced them with a section of rubber fuel line, they were also called a pulsator

Old Frog Enthusiast

Old Frog

Posted
  • Author
Posted

Jeremy WI'; Thanks for the info. I when by the parts dept. today with my VIN. The part descrition came up blank for the VIN. The parts guy was confused & said it did not make sense.

 

After I run the gas out of the tank, I will be going back to double check the tank & pump looking @ the connections & to check the voltage. I will look for the pulse dampener then. Thanks for the input post what I find.

Old Frog Enthusiast

Old Frog

Posted
  • Author
Posted

An update. I have run about 3 tanks w/ Lucas injector cleaner through the van over the past week (Kind of hurts With current gas prices) and checked & driven around with with a Scan Gage II connected. Any way, here is the update:

 

- Normal cold starts are still not happening if I simply, turn the ignition on, wait for the fuel pump to cycle & crank the engine.

- However, if I "pop" the ignition (simply a quick hit of the starter letting the engine rotate a couple of times, not a prolonged fast cranking speed) several times, (usually 2 to 4), the engine will start. If I have cranked the engine, it will take up to 5 pops of the ignition to start.

 

- No trouble codes stored in PCM and none developed during approx 300 mi. driving w/ the Scan Gage connected. Specifically, no misfire codes stored.

- Gage shows idle steady w/ an occasional 25 to 30 +/- fluctuation. The fluctuation is not rhythmic. The RPM varies slightly @ idle.

- Scan Gage voltage readings are interesting (A new charged battery) and the reading double checked @ the battery w/ a multi meter:

When the engine is running: @ 13.8 to 14. V.

When engine has been turned off after running: @ 13.2.

When engine is off in the morning, just before cold start: @ 12.2 V

- I have noticed that (new pump): 1. The fuel gage reading is a bit off (empty occurs @ about 1/8 tank) and 2. The gage will rhythmically fluctuate with in time with the blinker flash or fluctuate when an electrical load is placed on the system.

 

 

Based upon the above, I am inclined to think:

1. There is one, or possibly more, electrical problem(s). Something is dragging the battery down overnight and proper voltage is not getting to the pump.

2. That it is not an injector problem, particularly given the absence of no stored codes, particularly no misfire codes.

 

Any thoughts on this are welcome as are suggestions as to where to first look. Bob

Jeremy WI Enthusiast

Jeremy WI

Posted
Posted

Remove and clean battery terminals, might just be corroded. They must have gotten rid of the pulsator in 97, according to rockauto, you can't just replace the pump, you replace the sending unit

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • Atlas
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Atlas · Posted

      I will be doing that for sure, but I need to solve who has/ where I can find a bidirectional scan tool that will support OBD 1.5. I'm kicking myself because I ebay'ed a Snap On MT2500 that I didn't think I'd ever need anymore. D'oh!! I'd rather not buy another, so I'll contact a few local shops to see if they have one and how much they'd want to do the procedure. I'd rather have the ability to do it myself... I wish there was a modern tool that could do it all, but I'd have no idea what to buy.   The theory with the pulled timing is that it mimics a rich condition. The delayed spark causes incomplete burn and the O2 sensor picks up low oxygen levels. That's interpreted as a rich condition so the PCM pulls fuel and that shows up in the deeply negative fuel trims.
    • Chuck FB
      Joke Thread

      By Chuck FB · Posted

      An ultra wealthy man had the most beautiful daughter. But, there was a problem. Everything she touched would melt in her hands. No matter what, Metal, Wood, Stone. Anything she touched would melt. She could not feed herself. Because of this, men were afraid of her. Nobody would dare marry her. Her father was despaired. What could he do to help his daughter? He consulted doctors, scientists and anybody who could solve this problem. Finally one of them said, "If your daughter touches one thing that does not melt in her hands, she will be cured." He was overjoyed and came up with a plan. The next day, he held a competition. Any man who could bring his daughter an object that would not melt in her hands would be given billions of dollars to marry her. Three extremely intelligent and handsome young men took up the challenge. The first brought a very heavy steel rod, But alas, when the she touched it, it completely melted in a matter of seconds. He sadly went away. The second brought a beautiful diamond, knowing diamonds were one of the hardest substance in the world and would not melt. But alas, once she held it in her hand, it melted. He too was sent away disappointed. So now, there was one left He was very nervous & sweating. He approached the daughter & said, “put your hand in my pants pocket and feel what is in there." She did exactly what he asked. She felt something very hard. She held it in her hand, squeezing it as hard as she could. It did not melt & remained extremely hard. Her father was overjoyed. Everybody was overjoyed. She was finally cured. Nothing never, ever melted in her hand again. They married and they both lived happily ever after, raising a wonderful family. Question: What was in the the groom’s pants pocket??? Answer below ↓ M&Ms of course! They melt in your mouth, not in your hand. What on earth were you thinking?
    • asilverblazer
      Wow I'm in a pickle. (Broke down truck) and a story.

      By asilverblazer · Posted

      There's a bunch of tea leaves that you've read, but in any case the delayed timing is unusual. Not sure how that relates to the rich at idle vs. 'normal' while driving.   If you're in this deep, might be worth investigating, and re-learning the sensor. What have you got to lose? Plus, it properly fixes the timing cover leak.
    • asilverblazer
      Wow I'm in a pickle. (Broke down truck) and a story.

      By asilverblazer · Posted

      The only problem I have seen this cause is longer crank times. 
    • Atlas
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Atlas · Posted

      Injector is being sent off today for rebuild and I estimate I'll have it back in 10 days or so.   It may not be the injector...of course...now that I've torn down the intake again. But, let's rule out the injector and replace those spider legs that have been almost rubbed through.   The truck has always had negative timing and I'm reading "normal" timing at warm idle should be +16 or so. I'm negative 16 to 25 or more, and it's always been like that since I bought it.   A light turned on upstairs last night in the old noggin. Rare, I know...   This will be wild, if it turns out to be the cause!   In 2001, according to the old service documentation, the muffler was replaced. Why? I have no idea, it wouldn't have been rusted through by then. But they did a crappy job.   In 2019, another shop replaced it and noted the prior install was poorly done on the work order. "Exhaust system vibrates on crossmember". Except...I guess they just left it be? I believe the husband, the couple who were original owners, had passed by then. Maybe she said it's just not worth it to have the exhaust system fixed and declined repairs. Very few miles were driven between 2019 and 2025.   The exhaust system vibrates heavily on the crossmember and you can feel it and REALLY hear it, even today. Not always, but at idle, it gets going pretty good sometimes.   What if....   ....What if that's enough to trigger one or both of the knock sensors? Could it be tricking the sensors into sensing knock, so it's pulling timing aggressively? Pulling timing heavily means it's firing after the piston reaches full height which means incomplete burn which means the O2 sensor is sensing a rich condition, which means I've been chasing my tail, and what I thought was an inconsequential problem (janky exhaust) has been THE issue for this truck for 25 solid years?   That would be wild. Maybe it IS wild.   The service documentation thereafter, for years, shows visits for rough idle, replacing O2's, replacing the cat, replacing plugs and wires, a misfire condition, like they could never solve the issue. The injector has been replaced 4 times in 80k miles, that's just crazy.   The secondary theory....   The engine has clearly had a leak at the front seal for a very long time (the greasy trench...). I think the truck changed hands quickly ~2025 because there's Napa receipts from someone I don't recognize in the ownership history. They apparently replaced the timing cover seal, and they did a terrible job. There's RTV smeared all over and the leak I had reduced to a weep by snugging the front oil pan bolts is now a leak again.   HOWEVER....I read about replacing the crankshaft position sensor. Any time the ckp sensor is disturbed or timing cover is removed, the truck requires relearning, and that can only be done through a bi-directional scan tool. Skippy with the RTV probably didn't do the relearn procedure is my guess. His scan tool is lost in a pile of RTV goo somewhere.   So, it's very possible the sensor has been disturbed and the truck is just running on the old learn data but not setting a code for anything. The distributor has since been replaced and so has the camshaft position sensor, so all bets are off for that thing.   In the theme of one step forward, two steps back, I returned the accumulator for the AC. The gal I've been working with at O'Really's has been great. She refunded it under manufacturer's defect and we compared it to the replacement I ordered, and sure enough, the replacement is machined very differently (and a gauge actually fits on it!).   Got it home, installed it, started vacuuming it down.... and I couldn't get good vacuum.   The high side service port, where I replaced the old GM ball valve suspecting that was a source of the previous leak....well, I've clearly exposed whatever pre-existing crack in the line where the service port is welded, and made it much worse. Blessing in disguise? Except there goes another $25, now I'm waiting for a replacement AC line.   In 10-ish days ALL the parts will be here. Rebuilt injector, new exhaust system, new cat, new high pressure AC line.   Oh, did I mention the squeaking ISN'T coming from the AC pump? The truck still squeaks when started, and there were words after I started it with the new AC pump installed. But, there was more to replacing the AC pump for just a squeak. A truck with good working AC is something of value, for the comfort alone.   I've ordered a new harmonic balancer because, 30 years is a good run for one of those. Rule it out. The squeak may be something more sinister, though. I'm worried about that ckp sensor and if it was shimmed correctly, or if the timing set was installed correctly. The squeak may be coming from UNDER the timing cover.   At this point, once I get it put back together, I'm thinking I'll take a 50 mile victory lap and then promptly put it up for sale. This truck is cursed. Betty, from beyond the grave, doesn't want anyone messing with her Blazer. Or maybe she's getting revenge for 30 years of shop visits with that thing.

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...