‘97 5.7 Vortec - ̶n̶o̶t̶ your typical crank no start

[wyn97]

Update: I see no excessive play in the timing chain checking with the method described above. Less than 5 degrees of play. I re-checked the compression now that the truck isn’t stranded in the grocery store parking lot but is instead back home, and now I’m getting closer to 90psi on all cylinders. I believe I might’ve overlooked holding the throttle down and likely didn’t crank it long enough in the parking lot; I was too worried about shaking my booty for all the folks driving by I suppose. After standardizing my approach for each cylinder I’m seeing much more normal compression numbers. Without getting the engine warm I’m not too stressed about these being a touch low, until it doesn’t start after my next try.

1 90 2 110
3 90 4 95
5 75 6 90
7 95 8 85

I took the battery by the parts house so they could charge it (my battery charger disappeared with a neighbor about two months ago when they moved, mysteriously) and when I picked it up grabbed a new cam sensor/distributor module. Having pulled the distributor I see no signs of excessive wear on the gear and the roll pin is firmly affixed holding it in place. Everything seems mechanically sound as far as I can tell at this point.

Once I get back at it and swap the cam sensor out on the distributor, I’ll button everything back up and try again. After that fails I’ll just take the thing to the shop and let someone who’s getting paid 8 hours a day and knows a thing or two look at it. Maybe it did jump time after all, had the lifters go, maybe a magic unicorn fairy made sweet love to my pushrods while bending through time and space. Here’s hoping I don’t have to sacrifice my beer budget for someone else’s

 

[Awest623]

Sorry if I missed it. But did you check the distributor gear? I had one wear through on me and it had the exact same symptoms that you described.

 

[GoToGuy]

Thank god the compression came up. If you have a service manual you could see what the drivabilty diagnostics fits your known conditions, maybe narrow down which logic branch to follow. Good luck.

 

[Supercharged111]

Isn't compression usually higher when cold? That 75 hole is a bit more than 10% lower than the high hole and a bit more than 10% off the more median 90 holes.

 

[Donald Mitchell]

I had a situation with the engine quitting, then later it would start and was suspecting a bad fuel pump. Eventually I removed the cap and rotor looking for problems and found the connections and terminals to the module had almost rusted into, I dont remember finding it till I completely removed it. I hav also never seen another rusted like that, It was probably a chinese part. Good luck!

 

[Vort123]

I need some help from someone wiser than myself.

‘97 Vortec 350 has me stumped. I was driving it around town, running errands as one does. I got to my last stop of the day, and upon wrapping up and leaving the parking lot became stranded. I fired the truck up, and made it about 200 feet before the engine abruptly but without fanfare died. I attempted to refire it and was greeted with the sounds of the engine trying to start but not at all in a healthy way.

Here are specifically the symptoms I’m seeing:
Free cranking, sputtering but no running
Ether/starter fluid leads to a large fireball out of the throttle body
Gas directly in the intake leads to a backfire

Here’s what I’ve checked so far:
Fuel pressure, 60psi, and does not bleed off. (Not a blown regulator diaphragm)
Spark happens, at least on cylinder 1
Distributor turns, so timing chain is still there supposedly.
Low compression on 1-3-5-7 (60psi)
Cylinder 2 is at 115psi, 4 is at 60. I have not checked 6 or 8 yet.
Plugs were a little wet, from cranking so much with no running I suppose.
Distributor is tightly held down, the base does not turn.
The cap and rotor are brand new Accel parts. The coil is a brand new MSD coil. Plugs wires to match.

I think, somehow, my 25k mile rebuilt motor jumped time. With no tensioner in there I don’t have the foggiest clue how that happens but, if it quacks like a duck and waddles like a duck…

I used a code reader and got no codes displayed, and the data reads on all sensors I recognize. MAP, MAT, CTS, TPS, MAF, RPM, all read normal and respond under cranking.

The only other thought would be a bad distributor / cam sensor pickup. I don’t know how these respond and determine crank timing but if somehow the distributor pickup was giving poor data perhaps it could advance the timing enough to cause the fireballs on ether?

I am absolutely stunned but I am out of ideas. This truck is my daily right now, so getting it fixed is a priority for me. Where would those long in the tooth go from here? Check my work again? Tear into the top end and look? Leap into a river? Any guidance is appreciated.

Timing issues

 

[Vort123]

Timing issues

I’ve had the gear on a distributor sheer a couple teeth.had similar symptoms

 

[wyn97]

I replaced the module on the distributor to no avail. I unplugged the cam sensor, and she backfired worse through the intake with no ether. So, I put the balancer on TDC to check timing. It's really hard to tell with these crab cap dizzys but the rotor is pointed just at if not past the #1 post on the inside of the cap. If it jumped time it was a tooth or two at most.

The distributor gear looked good to my eye, no marred or missing teeth. I'm ordering a new one anyways, I can get an MSD Street Fire one for pennies on the dollar effectively, since the plastic bodied one I have is struggling to retain the cap after this round of diagnostics. I would think if this was the problem, that it wouldn't have been all of the sudden.

A handy friend of mine was able to track down a technical service bulletin pertaining to a no start/hard start occurring due to a faulty crank sensor that required a re-learn. Apparently a faulty crank sensor can cause timing to advance up to 50° only at cranking. This should throw a code however, and my scan tool does not show any codes stored. The only fix listed is a fresh sensor AND running the re-learn procedure. I've never worked on early OBD2 stuff to this capacity, so I don't have a scan tool / read-write tool that will work for that procedure. Both procedures involve getting the truck running, so, guess I'm SOL anyhow? Has anyone else encountered THAT problem? TSB and procedures attached.

I'm not going to lie, I'm not a mechanic by trade or by hobby, I have a breadth of experience but not depth, and I really don't enjoy this work that much, unless I end up with something faster that makes cooler noises ‍. This truck was meant to be a paid-off daily while I waited out the market to get a reasonable price on another daily driver, since it had such a low mile engine. I expected goofy things to happen, and wasn't exactly stunned at being stranded, however I really didn't think this thing would kick my teeth quite this hard. Just a bit of a vent to top off this empty post. More "idfk" to round out the evening.

Thanks to all that have offered their suggestions so far.

 

[SUBURBAN5]

I know this sounds dumb but your exhaust system isn't clogged right? Or at least messed up?

 

[CNY99K1500]

I need some help from someone wiser than myself.

‘97 Vortec 350 has me stumped. I was driving it around town, running errands as one does. I got to my last stop of the day, and upon wrapping up and leaving the parking lot became stranded. I fired the truck up, and made it about 200 feet before the engine abruptly but without fanfare died. I attempted to refire it and was greeted with the sounds of the engine trying to start but not at all in a healthy way.

Here are specifically the symptoms I’m seeing:
Free cranking, sputtering but no running
Ether/starter fluid leads to a large fireball out of the throttle body
Gas directly in the intake leads to a backfire

Here’s what I’ve checked so far:
Fuel pressure, 60psi, and does not bleed off. (Not a blown regulator diaphragm)
Spark happens, at least on cylinder 1
Distributor turns, so timing chain is still there supposedly.
Low compression on 1-3-5-7 (60psi)
Cylinder 2 is at 115psi, 4 is at 60. I have not checked 6 or 8 yet.
Plugs were a little wet, from cranking so much with no running I suppose.
Distributor is tightly held down, the base does not turn.
The cap and rotor are brand new Accel parts. The coil is a brand new MSD coil. Plugs wires to match.

I think, somehow, my 25k mile rebuilt motor jumped time. With no tensioner in there I don’t have the foggiest clue how that happens but, if it quacks like a duck and waddles like a duck…

I used a code reader and got no codes displayed, and the data reads on all sensors I recognize. MAP, MAT, CTS, TPS, MAF, RPM, all read normal and respond under cranking.

The only other thought would be a bad distributor / cam sensor pickup. I don’t know how these respond and determine crank timing but if somehow the distributor pickup was giving poor data perhaps it could advance the timing enough to cause the fireballs on ether?

I am absolutely stunned but I am out of ideas. This truck is my daily right now, so getting it fixed is a priority for me. Where would those long in the tooth go from here? Check my work again? Tear into the top end and look? Leap into a river? Any guidance is appreciated.

I'm new here and you may have already received a response about this, but I had the exact same thing happen on my 99 K1500 truck and a couple of times before on different gm cars. No codes, just sputtered and quit. It had spark but it was sporadic. The ignition module is bad. It's on the passenger side between the throttle body and valve cover. It has a 3 or 4 wire connection and a heat sink. I've owned a few of these trucks and when the thermal transfer paste dries out, it overheats the module cooking it. There used to be a way to bench test them and a few parts stores had testers years ago, but I'll try to attach a pic of the part.