EzPz

Howdy fellow Chevy fans! I'm new to this forum, and I hope someone with very good 5.7 Vortec CSFI experience can help me with a very common problem extremely difficult to resolve. I've spent hours upon hours reading through so much BS and disinformation online, and with nearly every single one of them, when it looks like I found someone who may have just solved their problem, they vanish, leaving the rest of us stuck; they don't share their solutions. Thus, I'm hoping for the opposite of that from here; I promise to share my success if so found.


For starters, I drive a 1999 Chevy Suburban which I've owned for 14 years, and she's been pretty good to me, with the exception of two failed intake manifold gaskets; I've since swapped them just recently (four months ago) to the new metallic/rubber gaskets which I suspect should last much longer than the plastic one.


SYMPTOM:


Engine began stumbling under moderate throttle about two months ago. Under heavy loads, a P0300 and P0305 trouble code was popped. Troubleshot that down to a crack distributor cap ear-bracket (screw mount), and replaced with new metallic-body distributor; that solved my misfire code, but my stumbling and jerking still exists; only no code is ever thrown. I've replaced all plugs, wires, and distributor (with cap), and still stumbles.


I've not yet changed my timing chain as I suspect it is possible my chain is worn beyond efficiency. However, this does not explain why my truck runs great during normal highway conditions (especially when the weather is cooler), but drives awful under moderate to heavy acceleration; especially when pulling a horse trailer. I almost broke down in Blairsville, GA last month while pulling a horse trailer up the mountains. With 4:10 gears installed, I've never had problem before. But this time, the truck in Low 2 barely made its way up the hill, with massive fuel loss, no power, and coolant temperature approach 230 degrees. It did better on the return, averaging about 16 mpg pulling a 3,000lb horse trailer; of course it was mostly downhill. Before anyone suggests my catalytic converters could be clogged, let me first state that I do not have an acceleration problem under WOT (wide open throttle), and my RPM's will max out close to 4,500 RPM. I know a clogged converter will not let most engines above 2,000 to 3,000 RPM, with very slow acceleration. My problem seems to be limited to partial open throttle demands.


WHAT I SUSPECT:


I've used my Actron scanner to monitor STFT and LTFT, both of which are below 10% percent. However, neither are exactly even. The Short Term Fuel Trim for Bank 1 tends to approach 9.5% percent during stumbling and hesitation, while the STFT for Bank 2 will remain around 4% to 6%. I still have not be able to determine the cause for a slight lean condition on bank 1.


I've performed vacuum checks, and all is good. I've performed the "rich" condition test with propane, and all worked as expected; the ECM reduced fuel demand, and the STFT began going negative (meaning the demand for fuel was decreased), but returns to normal once propane is removed (goes back to positive, closer to 0% - 3% percent (until moderate to heavy throttle).


FUEL PRESSURE TEST


Here is where I'm confused. The worthless Chilton repair book states that the fuel pressure on the 5.7 Vortect CFSI must be 60-66 psi "in all conditions". Here are my fuel pressure test results.


Static (key on engine off) - 3 second cycle to 60 psi, but then abruptly drops to 49 - 51 psi.


Engine running - Idle FP - 52 - 56 psi, but will momentarily climb to 59 - 60 psi under heavy snap-throttle. Moderate throttle shows little to minor climbs from 52 -54 psi. During deceleration from 4,000 RPM after snap-throttle, FP drops to about 46 psi, and takes a few seconds to climb back up to 52 - 53 psi.


Shut engine off - Pressure holds at about 40 psi after 20 minutes. With fuel pressure gage still connected, overnight the pressure is down to 0 psi (no pressure). Cycle key switch once, and FP only increases to about 20 - 30 psi. Cycle key switch 2nd time, and pressure climbs to about 50 - 52 psi. Third cycle, pressure cycles to 60 psi, and then drops to 50 psi upon ECM 3 - 5 second cut-out. I do not believe my fuel pressure regulator is bad. I do, however believe that my fuel pump might have a clogged strainer, or might be failing. The fuel pump was replaced 2 years ago and is an AC Delco. I know the Delphi pumps are much better. Unfortunately, because this is a Suburban, I am unable to perform a direct inline fuel-pump pressure test. I still need to perform an amperage test at the relay box to determine if the fuel pump is having to work hard.


OTHERS have stated similar problems to mine and claim that they've upgraded to the MFI spider assembly; a waste of money if you ask me considering nearly all of them did not solve their problem, despite the few who have stated otherwise. My biggest concern is with the cheap plastic tips they are using on the MFI's, which have a tendency to melt, making it impossible to remove without removing the lower intake manifold. Does anyone know if the Delphi MFI spider assembly have the same worthless plastic tips? Or are these melting problems limited to the AC Delco or after market garbage injectors?


I'm interested in anyone's advice. But I would appreciate responses from those who have experienced this problem. Trust me when I say, if I solve my problem, unlike the other a-holes on other forums, I will not simply leave; I will share my results. I look forward to your responses, and I would greatly appreciate any help with this ongoing issue.


SUMMARY:


99 5.7 Vortec stumbling under moderate or higher loads, loss of power under moderate to heavy load, jerking, and poor fuel economy during acceleration. Normal driving averages about 17 - 19 mpg. I've replaced plugs, distributor, cap/roter, wires, mass-airflow sensor (don't ask...ruined old one with incorrect cleaning methods), and fuel filter. I suspect possible timing chain has loose chain (although not getting P1345 code), weak fuel pump, or the stock spider injector assembly. I do not believe my fuel pressure regulator is bad as my pressure maintains at least 40 psi after 20 minutes to an hour, yet drops to 0 psi over night.

voypro

To EVERYONE that is experiencing odd problems. First thing first visual check your computer location (the cars brain) and eliminate it from the possible list of problems. For a few years Chevy put the computer (in aluminum clamshell like box) directly under the power steering fluid, brake fluid reservoir, windshield wiper fluid and at a location where rain pours directly on top of it. There are 4 wire harnessed that attach to it ... 2 on top 2 on bottom. Often the pin connections in the wire harness get corroded, from the fluids. This causes random acceleration problems. I experienced engine hesitation problems and Poor acceleration when I gave her the gas. (Some of the pins most affected go directly to each injector in the spider fuel injector)

Also mine threw three simultaneous O2 sensor failures. Again, all caused by corrosion in that wire harness.

The corrosion can be so bad that isn't possible to remove the bottom wire hardest connections, without tearing out pins in the connector (if that happens you're going to need to change those anyway) Furthermore the location of these computers beneath all of the fluids caused such tremendous amount of corrosion inside the clam shell casing that your computer Circuit board can covered with thick layer of aluminum oxide powder which can play hell with the computer. Mine was so corroded that four of the 10 bolts head that held it together had been pop off from the internal pressure of the corrosion.

Also, If you ever change out a wire harness be sure you do not cut your old one off without marking the location of each wire. Because you'll find that there are several of the same wire coloring that go to various pins.

Eliminating the computer as the problem should be your first step if your computer location's place underneath the aforementioned liquids.

EzPz

Thanks for the recommendation. My PCM is located atop of the driver-side wheel well underneath the hood. I suspected that when this all began. So I removed the PCM and checked the wiring harness connections, and there was no corrosion. I've also disconnected the spider assembly electrical connector and attached a node-light to test for possible circuit failure and the light flashed with each injection attempt. So at this point, I do not believe my PCM or the wiring harness to be the culprit, although I will not rule out the possibility of a faulty PCM. I only wish I had a scanner that could show me exact misfire numbers if such exists, although I have not been getting the P0300 or P0305 misfire codes ever since I replaced the cracked distributor, and everything else.

I really wish I could get my hands on a quality Tech2 scanner so that I can read possible misfires from any of the cylinders.

Today I performed a series of fuel-pressure tests; especially by crimping the return line, and the fuel pressure exceeded 60PSI but with horrible idle conditions as to be expected. I also decided to remove Banks 1 and 2 #1 O2 sensors to check for possible corrosion due to excessive antifreeze burning months ago prior to replacing the intake manifold gaskets. Both were deep ashy white, and so I cleaned them. I even swapped them out installing original Bank 1 O2 sensor on Bank 2, and Bank 2 O2 sensor into Bank 1. After driving, there was moderate improvement.

What concerns me about the graph reading from both O2 sensors is with the engine at idle, the roller-coaster fuel curve you're supposed to be reading fluctuates dramatically during rough idle. Instead of a nice smooth up-and-down curve, occasional spikes (up or down) happen.

I wonder if my O2 sensors need to be replaced. Any thoughts on how to troubleshoot a faulty or intermittent O2 sensor?

I'm one of those people who refuses to simply buy parts out of mere suspicion; I try to be as thorough at testing as I can. And right now it appears neither O2 sensor is operating smoothly at idle. Of course this could still be a fuel-delivery problem, and I won't rule out the possibility of sticking poppets. However, with sticking poppets, fuel pressure drop should be evident, which I am not seeing at this point. And the MFI spider assemblies are so expensive.

As stated about my timing chain, I do know that my chain as about 16 degrees of slack based on the backlash measurement on the harmonic balancer to distributor rotor button play. And my engine is has 198,000 miles on it, and my chain has never been replaced. So I wonder if a loose timing chain will cause stumbling. Is this true?

Joe

EzPz

Howdy GM lovers! Here's a follow up to my 99 Chevy Suburban stumbling problems.






Today, I finally decided to swap out my CSFI to the MFI upgrade. Upon removing my upper intake plenum, I inspected for possible cracks or damage, and wouldn't you know it! The plenum seal was not seated, and apparently kinked during installation four months ago after replacing the lower intake manifold gaskets. So that is probably what caused the stumbling, although I am still uncertain. I performed a vaccum leak test several times, I could swear that no indications of a vacuum leak were identified. My guess is that the leak was very small, but enough to cause a minor lean condition. But it still shouldn't stumble as it was doing; especially under partial to wide open throttle, where a minor leak would not be recognized. Anyways, the plenum seal was definitely not seats in its slot, and was folded. So I had to use sealant to hold the seal into place before re-installation.
Another problem I found were three leaking fuel injector tubes protruding out of the base. I saw fuel wetting underneath the tubes for cylinder 3, 5 (Bank 1) and cylinder 6 for bank 2. This is what likely caused my fuel pressure loss while sitting overnight. It might also explain the dramatic loss of power when trying to climb a hill last month in Blairsville Georgia.
I replaced the old leaky CSFI with the highly coveted MFI system, put everything back together, and test drove it for 67 miles to allow the computer to relearn my driving characteristics. And so far, she runs great, is more responsive, and is not stumbling or missing. However, I did notice that the computer-controlled Ignition Advance Timing (read on the scanner) kept fluctuating between 32 - 49 BTC at 2,000 RPM on a steady travel as 75mph. My distributor is new, but I'm quite certain my timing chain is worn (about 18 degree based on slack calculations). If the timing chain is too loose, my theory is that the ECM is constantly having to relearn timing, despite the crank-shaft to cam-shift sensor correlation is within the +/- 6 degrees. So while the engine is running much better than before after repairing the leaking plenum seal, and replacing the spider injector assembly, I believe the engine will run near 100% percent once the timing chain has been replaced.
More to come folks. As promised, I will not leave anyone out of the loop for those who have had similar problems as mine.
Joe

Gmc tater

Hello , I am currently having a bad encounter with my truck . It has real bad power loss at times and when it wants it runs like a champ. Driving down the hiway I step on the gass pedal to punch it into passing gear and it seems like I switched from drive to neutral. It's sputters a bit and then I easy off and then regains power. I have changed the o2 sensors note all 4. Sparkplugs and wires distributor cap and rotor. Tps sensor maf flow sensor. Egr sensor, ignition coil. New fuel pump and fuel filter. Added Lucas and seafoam . New air filter and still no improvement. I really want to get this truck running right I know it has alot of power and I'm not seeing it right now. I especially don't want to hear that dreadfull I TOLD YOU NOT TO BUY THAT OLD TRUCK MY WIFE ! please help thanx.

EzPz

When checking for vacuum leaks, a code reader with the capability of monitoring real-time fuel trims will help identify the possibility of a vacuum leak. If the 5.7 Vortec has any kind of vacuum leak (even a small one), the LTFT and STFT will begin to rise, usually above 10. This is because the detects more air than fuel mixture and so the PCM tries to compensate for the unaccounted for air by adding more fuel. If the LTFT and STFT remains near "zero" or +/- 10, then all should be well...SHOULD be well.


Another way you can check for vacuum leaks is to pick up a can of carburetor cleaner and begin spraying around the edges of the intake manifold. If the engine tries to stall, then you know you've got a leak. Most vacuum leaks are caused from poor mechanical practices when replacing the pesky intake gaskets. The newer gaskets have a thicker rubber on them with a metal strip, and has been known to cause leaks when not properly torqued with a torque wrench.


Reading some of your earlier posts, and learning that Bank 1 (driver side: 1,3,5,7) is misfiring seems to indicate a harness or PCM problem. HOWEVER, there is another common problem with these engines from the 1996 - 1999 models. The late model 5.7 vortec heads are lighter than older heads because GM tried to lighten them up by shaving as much metal off as they could. Unfortunately, this leads to LOTS (and I do mean LOTS) of late model vortec heads cracking, usually between cylinders 2 and 4 on Bank 2, and 3 and 5 on Bank 1. I noted you performed a compression test, but these are not always conclusive; dry or wet. Do a leak down test to see if the cylinders are not holding pressure. This will also help determine if you have a failed head gasket.


Fuel and air requires near perfect mixture in order to combust sufficiently. If the mixture is too lean or too rich, combustion is not at optimum performance. To make matters worse, if a cracked head or blown gasket causes slight compression lost under heavy load, the fuel will not combust correctly and thus cause a misfire. The PCM cannot directly determine which cylinder is misfiring accept by rapid RPM loss at a given degree. If the same cylinder keeps misfiring (I believe after 50 consecutive times), the misfire code will be given (check engine light) P030X with X being the specific cylinder 1,2,3,4,5,6,7 or 8).


Also, on some occasions, the camshafts on these engines wear down due to improper oil change frequencies. Although this is rare.


Right now, I've spent almost $2,000 dollars troubleshooting my continued misfiring problems on cylinders 3 and 6 but mostly 6. As with everyone else, I've replaced all ignition components (to include the distributor) to no avail; even the spider injectors to the MFI upgrade; no luck to fixing the problem. One day I decided to pull my heads off, and there it was!!!! Bank 2 head (cylinders 2,4,6,8) was cracked in three placed; the worst crack being on cylinder 6 between the intake and exhaust port; no repair possible! And heads are too difficult to find (high quality heads). Standard factory Vortec heads come a dime a dozen, but they are crappy and prone to cracking. DO NOT buy GM heads from 96 - 99. Pick up a set of nice performance heads with at least 63cc; the higher cc heads will cause compression issues unless you go to a larger cam.


In summary, I'm willing to bet you either have a PCM problem, or your bank 1 head is severely cracked or head gasket is blown.


Keep me updated.


Joseph

EzPz

Any fault codes?

psychosurveyor

Hello,
just wanted to chime in and say i bought a 97 sububan from a coworker about 2 years ago. it ran like **** on 6 cylinders cause of cracked heads (2 and 4) drove it 700 miles to my girls dads garage and started this whole r and r shabang off. there is nothing and i mean nothing that is not new on this motor 3000 deep on top end. (paid 500 for it) . has been a super super truck since new delphi fuel pump spider jeez name it i put it on. just as of yesterday she quit just quit messed with it today all day first no start then started rough then run good then started putting out strange white smoke under the hood didnt smell normal either then went back to no start again. ive got the patience money and know how to go back to fighting this thing but is there any other person seen this before?

oh yeah i did do the im tired of working on it deal and didnt replace any sensors since it did so well could a sensor cause such a ruckus? its almost like it is going in and out of time

the smoking thing though scares the crap out of me its coming from under hood. i have noticed talk about crank sensor jumping 50 deg. going back at it tomorrow changing maf and crank sensor see what happens.

psychosurveyor

distributor is original though but has the expensive brass cap and rotor because of the condensation problem vortec v8 have

Mr camshaft

Take the upper plenium off, on the side that is sooting the plugs, take an injector from the intake one at a time & get a friend to switch the truck, don't crank it just switch it to make the fuel pump run, if gas runs or trickels out of any of the injectors odds are good you got a burned out PCM . I read a while back that when an injector shorts out it will eventually short the PCM controls & it will leave the injector open when it's just switched​. I may be wrong but it's worth a shot. Be careful with the fuel. To everyone else I know this is not the way to post, but I'm new & I really think that is his problem, sorry.