'94 350: good cold starts, struggles to crank when restarting or still warm

kenh · Nov 26, 2020

thinger2 said:
Its just a grounding problem.
Or at least you cant diagnose it untill you check out all of the grounds.
Take a look at the ground strap from the back of the passenger head to the firewall.
It shares a common lug with a strap that goes to the frame.
A real ***** to get at which is why they never get checked.
Your ecm and sensors have a ground to a stud right next to the manifold temp sensor.
check those out, not with a meter, continuity doesnt mean **** of of the meter.
Pull them all apart, clean em up put new good quality heat shrink connectors on.
The starter grounds to the block, the block has a few grounds but they ground in different "planes"
In other words those grounds are providing a path for different sources.
If you are missing a ground or have a weak or intermittant ground, The path then goes through whatever other ground it can find.
It just wants to go back home.
If you have no grounds, it will go through the transmission cable or the throttle cable or even the main bearings or the transmission.
So, before you go too nutty brother.
You cant diagnose a gm tbi unless all of the grounds and power are good and solid.
Crawl up and under and all over it and fix all of that every damn bit of it.
Live data does not mean **** all of anything if it is from an ungrounded or intermittantly grounded systen.

^^^^^^^^^^^ YES!!

ALL vehicles since the invention of the computer are much more sensitive to grounds that pre computer. Flaky grounds cause more issues than you can imagine!!! Like I mentioned before, after I cleaned all my grounds my intermittent hot start issue disappeared. I used a scotch bright pad on my die grinder to clean the block and firewall connections and any other ground point. The engine seems to run better/smoother. That is as long as the ICM works. LOL

BITE THE BULLET and clean the grounds (includes dropping the starter and cleaning the block) and then see where that takes you.

Ken

usar17 · Nov 27, 2020

Just waiting on parts to come into. Between that and deer season I'll find time to get the truck on the lift.

I plan to:
-remove starter and clean mounting surface to engine block
-remove all grounds and positive cables
-clean all grounding spots
-install starter heat shield
-new knock sensor while I'm in there
-new AC Delco #2SD42XE positive battery cables with main 2awg to starter
-new AC Delco #2SD33XA negative cables with main 2awg to block and 8awg to front clip
-additional 4awg grounds from battery to frame and firewall

Now thought, only bc I see new vehicles and boat motors this way... Should I paint over or spray rubber or some degree of a coating over the grounding spots to encapsulate them? Or is this pointless?

Sent from my SM-G981U using Tapatalk

Nautique454 · Nov 27, 2020

My '95 was doing that (good cold starts, hard warm starts); it ended up being corrosion on the battery terminals. I cleaned them up and it works perfectly again.

Andrew7 · Nov 27, 2020

On my 93 C3500 we added a cellenoid. Also replaced cables, etc

Schurkey · Nov 27, 2020

usar17 said:
Should I paint over or spray rubber or some degree of a coating over the grounding spots to encapsulate them?

The Bus Company I worked at used to use Glyptal paint for that, then stopped with the Glyptal and used NYK grease instead. Also sold as a "Truck Lite 77" product at any NAPA.

https://www.amazon.com/Truck-Lite-9...d=1&keywords=NYK+grease&qid=1606510168&sr=8-1

(I preferred the Glyptal, as it wasn't as messy when you bumped against it.)

thinger2 · Nov 27, 2020

The ground strap from the back of the passemger side head to the firewall and from the firewall to the frame are pretty well known to cause intermittant ground loss as they move around.
A good way to test this is to check continuity while holding one probe on the strap and moving it around.
Its easier if you have a meter with a "tone" feature so you can just listen to it but just watching the meter works fine.
You can often move that strap around and loose continuity
In the old days the heads were grounded to a valve cover bolt but with center bolt valve covers that doesnt work.
But that bad ground will cause all kinds of issues it can even foul the plugs.
And coating the connections after all is repaired deffinetly helps.

Nad_Yvalhosert · Nov 27, 2020

Andrew7 said:
On my 93 C3500 we added a cellenoid. Also replaced cables, etc

Solenoid?

Sam Cooper · Nov 28, 2020

DerekTheGreat said:
Like you said in your first post at the end, your timing might be too advanced. Especially with the knock counts being so high like that. I'd verify that first before firing the parts cannon and replacing the knock sensor, as it costs zero dollars to do that if you already have a timing light. To do it, get the engine up to operating temp and then shut it off. Make sure the ignition is off and unplug the tan wire with black stripe located under the cover panel on the passenger side firewall. Re start the engine and check the timing. SHould be set to zero. If it isn't, put it there. I don't care what some Jim-Bob tells you about advancing the timing, just put it to zero. These are happiest there and the computer will pull the timing out anyway once it sees knock. Once you're done, shut the engine off, reconnect that connector and button everything back up. Observe any changes/improvements.

I have two tbi OBD-1 trucks. Both of them had the same hard start conditions. I did all the old school checks and repairs, including large gauge cable to starter. In both cases, I found the timing was not changing when I disconnected the timing connector. So in both of my trucks, I replaced the ECM, set the timing at zero so it will retard the timing to make starting easier. They both immediately started much easier, idle nicer and have more power. I'm not yet too old to learn new tricks.

Frank Enstein · Nov 30, 2020

95% of my electrical calls are bad grounds or bad connections. The other 5% are reading instructions to adults.

Schurkey · Nov 30, 2020

Frank Enstein said:
95% of my electrical calls are bad grounds or bad connections. The other 5% are reading instructions to adults.

I don't know if that's better or worse than my typical electrical/electronic repairs.

35% broken wires, corroded wires, corroded or otherwise non-conductive joints--failed solder joints, failed crimp joints, failed nut-on-stud or bolted-together connections, corroded contacts in molded-plastic connector bodies, corroded battery clamps, etc.

35% failed electrical components--dead "modules", fried circuit boards, junk starters/alternators/regulators/ECMs, worn-out fuel pumps or relays, burnt-up HVAC blower motors, worn-out contacts in switches, etc.

20% UN-DOING (or RE-DOING) AFTERMARKET JUNK (or prior "repairs") that weren't installed properly to begin with. From one perspective, it's just more examples of the first two things I've listed. Careless installation of stereos, auto-starts, alarms, aftermarket lights, etc. Often bottom-feeder electrical components--cheap switches, wire nuts, lack of heat-shrink tubing, circuit boards that aren't robust enough to survive in an automotive environment, all of which sometimes is installed by a baboon. What could go wrong with that?

10% weird ****.

'94 350: good cold starts, struggles to crank when restarting or still warm

kenh

I see nothing I hear nothing

usar17

OBS Enthusiast

Nautique454

Newbie

Andrew7

Newbie

Schurkey

Supporting Member

thinger2

I'm Awesome

Nad_Yvalhosert

I'm Awesome

Sam Cooper

Newbie

Frank Enstein

Best. Day. EVER!

Schurkey

Supporting Member

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