1994 TBI 350 Stretched Timing Chain

[megafan0258]

Hello all!

Long time thread lurker here.

I've been chasing a problem with my 94' for over 2 years now. It began as an idle surging issue, developed into "laggy" throttle response and has ended in a lean back firing issue.

After replacing and testing and replacing and testing part after part, checking all my grounds, I finally did a compression test. These are my results:

8-148 7-152
6-152 5-145
4-147 3-150
2-150 1-140

I performed this cold due to having headers. I put some oil in 1 being the outlier and it rose to 150. Considering the engine has 180,000 miles and a questionable maintenance history, I am pretty happy with that.

I got sick of waiting for my ALDL cable to ship from RedDevilRiver so I cracked open the timing cover and found a nice surprise. The Ole man kept telling me it's a timing issue and that the chain is stretched. I'm thinking he was right.



Looking for input from others on their experiences with timing chain stretch.

Thanks!

 

[Schurkey]

I've seen WAY worse.

Chain slapping so hard that it wears a hole in the timing cover, for example.

It's opened-up, I guess you might as well toss a (quality!) timing set in there. DEGREE THE CAM when you do.

Your cranking compression numbers are about what I'd expect. They're fine. I quit doing "wet" (oil-added) cranking compression tests ages ago. I don't see how oil squirted in the spark plug hole on a slanted cylinder bank--"V" engines, slant-4s, slant-6, etc. can climb to the high-side of the piston to wet the rings. The compression pressure increases because the oil you pumped into the cylinder is not compressible, it essentially reduces the chamber size, increasing the compression ratio.

As for the actual driveability issues, I suggest

The Usual Three:

1. Verify fuel pressure at prime, at idle, and under load. Most fuel pressure gauge assemblies have a push-button pressure release connected to crappy vinyl tubing. Route the tubing so it empties into a drain pan, then push the button while the engine is running. This simulates higher fuel demand if you can't check fuel pressure on the highway. Fuel pressure should remain steady even with fuel flowing down the pressure-relief tubing. How old is the fuel filter? Have you ever dumped a bottle of Chevron Techron Complete Fuel System Cleaner into the gas tank? (Recommended at every oil change.)
   
2. How old are the usual “tune-up” parts and procedures? Inspect/replace distributor cap, rotor, plug wires, spark plugs. Make sure the ignition coil will reliably fire a spark-tester calibrated for HEI when the coil is fully warm, and misted with water from a squirt-bottle. Cranking compression test of all cylinders while the spark plugs are removed. Verify EGR, PCV, EVAP, and Heated Air Intake (if used) systems for proper operation. Verify proper initial timing (TBI) and electronic spark advance (TBI and Vortec). Replace old O2 sensors unless you can PROVE that they're working properly—old O2 sensors get lazy, they don't provide accurate data, but they do provide “data” that fools people into thinking they're “working”.
   
3. Connect a scan tool (NOT a crappy “code reader”) and look for “codes”. More important, look at the data stream to verify EVERY sensor and computer output. Verify fuel trims during the time that the vehicle is not running properly. Look for misfire counts for each cylinder (OBD2 only.) “Codes” have official diagnostic procedures that will be found in the service manual set for your vehicle. The service manual set can be downloaded from the links in the Sticky thread section of the Engine forum on this web site.

 

[megafan0258]

I have a Cloyes C3055 timing set. As for degreeing the cam, I don't have a degree wheel and didn't really plan on doing that.

You're recommendations for the drivability issues have already been conducted. See list of items replaced and tested on truck:
- Plugs/wires (AC Delco/Taylor)
- Distributor (Jegs 555-40006)
- Coil (Standard Blue Streak **Tested**)
- Multiple MAP sensors
- GM CTS **Tested**
- AC Delco TPS **Tested**
- WVE 4F1014 EGR **Tested**
- Multiple IACs
- TBI Rebuilt w/ Reman Injetors
- Bosch O2 sensor
- ALL grounds redone with new straps or eyelets.
- MAP, TPS, CTS, IAC pigtails replaced and double check for being correct.
- Delphi Fuel Pump **PSI tested/not volume though**
- Intake Manifold Gaskets

I've also a done the following as an aside:
- Full stainless exhaust (PowerGo Motorsports 304 Shorty Headers, CATCO CTO-9648 Y-pipe/Catalytic converter, Gibson 615576 Cat back)
- Powermaster 140 Amp Alternator
- Nylon Fuel line kit.

I've went through most everything on my truck BESIDES having a live data stream.

As I mentioned before I purchased an ALDL cable from RedDevilRiver but I got a tracking number just this Monday after purchasing 8/25.

 

[rebelyell]

I have a Cloyes C3055 timing set. As for degreeing the cam, I don't have a degree wheel and didn't really plan on doing that.

You're recommendations for the drivability issues have already been conducted. See list of items replaced and tested on truck:
- Plugs/wires (AC Delco/Taylor)
- Distributor (Jegs 555-40006)
- Coil (Standard Blue Streak **Tested**)
- Multiple MAP sensors
- GM CTS **Tested**
- AC Delco TPS **Tested**
- WVE 4F1014 EGR **Tested**
- Multiple IACs
- TBI Rebuilt w/ Reman Injetors
- Bosch O2 sensor
- ALL grounds redone with new straps or eyelets.
- MAP, TPS, CTS, IAC pigtails replaced and double check for being correct.
- Delphi Fuel Pump **PSI tested/not volume though**
- Intake Manifold Gaskets

I've also a done the following as an aside:
- Full stainless exhaust (PowerGo Motorsports 304 Shorty Headers, CATCO CTO-9648 Y-pipe/Catalytic converter, Gibson 615576 Cat back)
- Powermaster 140 Amp Alternator
- Nylon Fuel line kit.

I've went through most everything on my truck BESIDES having a live data stream.

As I mentioned before I purchased an ALDL cable from RedDevilRiver but I got a tracking number just this Monday after purchasing 8/25.

C3055 is a Heavy Duty set; that's a good thing. So, get on with the TC set swap and let us know.

 

[pressureangle]

Hello all!

Long time thread lurker here.

I've been chasing a problem with my 94' for over 2 years now. It began as an idle surging issue, developed into "laggy" throttle response and has ended in a lean back firing issue.

After replacing and testing and replacing and testing part after part, checking all my grounds, I finally did a compression test. These are my results:

8-148 7-152
6-152 5-145
4-147 3-150
2-150 1-140

I performed this cold due to having headers. I put some oil in 1 being the outlier and it rose to 150. Considering the engine has 180,000 miles and a questionable maintenance history, I am pretty happy with that.

I got sick of waiting for my ALDL cable to ship from RedDevilRiver so I cracked open the timing cover and found a nice surprise. The Ole man kept telling me it's a timing issue and that the chain is stretched. I'm thinking he was right.



Looking for input from others on their experiences with timing chain stretch.

Thanks!

Here's a horror thought; truck 5.7 still has flat tappets. With that many miles and 'unknown' history, you may be losing an exhaust lobe. Traditionally, your symptoms fit. Ultimately, when the lobe is pretty close to round, the cylinder charge retains enough pressure to light off what's in the intake manifold, usually worse with increased throttle. It's an easy check, pull the valve covers. You might do a vacuum test, if you have a high fluctuation in manifold vacuum it's most likely the cam. Best part is, you're already there!

 

[pressureangle]

Here's a horror thought; truck 5.7 still has flat tappets. With that many miles and 'unknown' history, you may be losing an exhaust lobe. Traditionally, your symptoms fit. Ultimately, when the lobe is pretty close to round, the cylinder charge retains enough pressure to light off what's in the intake manifold, usually worse with increased throttle. It's an easy check, pull the valve covers. You might do a vacuum test, if you have a high fluctuation in manifold vacuum it's most likely the cam. Best part is, you're already there!

Oh BTW, I have a very nice, 70k mile 5.7 with 1.55 true ratio rockers sitting on a pallet in Windham, Ohio, if you find the need.

 

[megafan0258]

C3055 is a Heavy Duty set; that's a good thing. So, get on with the TC set swap and let us know.

Thank you for the reply! I had no idea it was a "heavy duty" set. It just seemed good for the price, being made in the USA and all. I bought the set along with an oil pan/ timing cover gasket, oil pump and rear main years ago just in case.

 

[megafan0258]

Oh BTW, I have a very nice, 70k mile 5.7 with 1.55 true ratio rockers sitting on a pallet in Windham, Ohio, if you find the need.

One of the first things I checked was vacuum and have checked it so many times since that I forgot to mention it. 19-20 inches of vacuum steady, unless the idle starts bopping around which happens at random.

I'd love to slap a nicer engine in old gal but we need a new roof in the next year or two. Thank you for the offer, hopefully I won't have to take you up on it!

I'll keep the thread updated as I go.

 

[rebelyell]

your 94 truck is about when GM switched from M55 to M155 pump. M55 has 5/8" OD pickup tube and newer M155 has larger diameter 3/4" tube. GM & Melling engineers studied it and found the larger inlet helps stabilize pumps' low-to-mid-rpm performance --- where you spend majority of time. Hope ya ordered pump w/ larger inlet & matching tube --- suggest don't reuse such an old tube & screen either. Also suggest disassemble new pump and rinse it out w/ brake-carb cleaner as well as new screen-tube.

 

[megafan0258]

your 94 truck is about when GM switched from M55 to M155 pump. M55 has 5/8" OD pickup tube and newer M155 has larger diameter 3/4" tube. GM & Melling engineers studied it and found the larger inlet helps stabilize pumps' low-to-mid-rpm performance --- where you spend majority of time. Hope ya ordered pump w/ larger inlet & matching tube --- suggest don't reuse such an old tube & screen either. Also suggest disassemble new pump and rinse it out w/ brake-carb cleaner as well as new screen-tube.

I got a Sealed Power 2244146, which is a Mellings M55 with the 5/8" pickup tube. I forget how I arrived that being what i needed but it what I got. I planned on cleaning the pickup and reusing it, also tack welding it in place. We shall see what the engine came with stock when I pop the oil pan off.

I will clean up the new oil pump, which ever size it maybe. Thank you for that suggestion.