Needing some help from the 5.0 gurus around here

Jody Treadway

Jody Treadway

Croc wearing fool
Moderator
Joined
Mar 20, 2005
Location
Hendersonville, NC
As part of my recent build, I pulled the old 302 out of my Ranger and swapped in a "built" one. Still a 5.0 block, same wiring etc. Not a complicated swap. But...

I installed it, got it running and running well as of the weekend before last. I even linked a video of it running. The next day I installed my full hydro, ran it for an hour to bleed the system and called it a day. Fast forward to Tuesday of last week and it started backfiring at idle and especially when revving. Now, it won't start at all, just cranks...

I help a lot of people on here with their own driveability issues and I'm pretty darn good at it but this one has me stumped. Nothing changed whatsoever between Sunday and Tuesday, just the date.

It's a 5.0 based engine, really good heads and bottom end. Cam is a custom Comp, but not much more than a good low RPM torquey one. Nothing exotic whatsoever there. 30# injectors with matching MAF.

-A9L PCM with Painless harness. They have been on the truck for years
-I have strong, consistant spark at the coil, cap and each cylinder
-I have 42 psi fuel pressure and injector pulse present on all 8 injectors
-I have 175 psi compression on all 8 (she's got some bump :D)
-Cam timing and ignition timing are verified good
-I have installed known good PCM, MAF, TP, distributor, coil, plugs,etc with no success.
-No codes stored aside from the deleted emissions items. Been that way for years.
-PCM is getting the PIP signal from the module/stator
-All PCM grounds and powers have been verified

I am very well versed in the 5.0 world and this one is eating my lunch. I need it to run so I can finish it up for Harlan next weekend. Any ideas from anyone?
 
Looking at this I can see why you are stumped. If you have spark, fuel, and compression it should run.
 
Not a clue but I'm curious to the outcome. My guess would be to check timing and make sure it isn't way off.
 
If cam timing and spark timing are, in fact good.
Fuel pressure and volume are good.
Compression and spark are good.
All sensors are good, etc.

The only other 2 things that come to mind is actual air intake flow or fuel delivery timing....
 
I really think the vehicle is just a POS and you need someone to haul it off and get it out of your hair for you so you can go on and enjoy life.

You've helped me out enough over the years, I'll do it for you.
 
Cam timing has been verified as the crank is at TDC (#1 compression) on the cover at the same time the rotor is pointing at #1 on the cap.
Ignition timing is also verified as well via similar method. Also, none of that changed between Sunday and Tuesday.
 
Im sure you are 27 steps past my simpleton reasoning. Where I was going with the timing thoughts, had a 5.0 once that was getting a bad reference signal and was injector firing on exhaust stroke. Spark timing was right, valve timing was right. Injector pulse was in left field. took forever to figure it out. It was firing a spark into a dry chamber...
 
That's what I suspect @Ron.
Now I just need to figure out what is causing that issue.
Going to inspect the harness and especially grounds this afternoon
 
Sounds like timing issue like others have mentioned, possibly something loose or sensor going causing ignition timing to start going advanced... Would cause your idle/revving misfires and backfires.

But another thing to consider, if you know you have fuel/spark/compression could it have developed a relatively large vac leak? If a gasket is sucking in it could run fine for a while then as it sucks in start causing your backfires due to lean condition. That would also make it very difficult to get started.
 
Years ago on my CJ I had similar issues. Never could find the issue. Towed it to the shop and the distributor bracket bolt was loose and let the distributor to slowly work its way out of timing where it eventually wouldn't crank.

If timin was checked previously and was OK, maybe it slowly worked its way off during idling...
 
Are you using a timing light to verify timing with spout disconnected?

Timing should be set with the engine running but at least this would give you an idea where you're at.
 
Will it fire/run on starting fluid?
 
broncosbybart said:
Are you using a timing light to verify timing with spout disconnected?

Timing should be set with the engine running but at least this would give you an idea where you're at.
Click to expand...

I initially set the timing last week with the spout disconnected to 9* after it was warm. It ran the whole next day as such.
 
rockcity said:
Years ago on my CJ I had similar issues. Never could find the issue. Towed it to the shop and the distributor bracket bolt was loose and let the distributor to slowly work its way out of timing where it eventually wouldn't crank.

If timin was checked previously and was OK, maybe it slowly worked its way off during idling...
Click to expand...

I thought about that as well, but that was ruled out. As recent as yesterday I swapped in a known good dizzy and re-verified timing.
 
I like Ron's idea but I'll at least give you a 4Runner in trade to sweeten the deal. :D:lol:

You've covered everything I could have thought of for a 5.0 so far. Last time this happened to someone I know (similar engine build just with a big bottle on it), it was a ground issue. Only difference was he still had most of the factory harness not a Painless. Cleaned all of the grounds and reattached them and it worked fine after that.

I know this next theory is completely out of left field, but didn't auto 5.0's run an A9P and manual 5.9's run the A9L. Something having to do with spark advance and sensor voltages? Its been too long since I have really messed with 5.0's but I remember having to change ECU's before when converting a car. Of course this doesn't make a lick of sense because your's has run an auto for a while on that ECU without issue so I am just spitballing here.
 
StretchASU said:
I like Ron's idea but I'll at least give you a 4Runner in trade to sweeten the deal. :D:lol:

You've covered everything I could have thought of for a 5.0 so far. Last time this happened to someone I know (similar engine build just with a big bottle on it), it was a ground issue. Only difference was he still had most of the factory harness not a Painless. Cleaned all of the grounds and reattached them and it worked fine after that.

I know this next theory is completely out of left field, but didn't auto 5.0's run an A9P and manual 5.9's run the A9L. Something having to do with spark advance and sensor voltages? Its been too long since I have really messed with 5.0's but I remember having to change ECU's before when converting a car. Of course this doesn't make a lick of sense because your's has run an auto for a while on that ECU without issue so I am just spitballing here.
Click to expand...

I'm headed to Carquest today after work to grab a spool of 8 gauge black wire. I'm going to ground every frikken thing.

The A9L is a manual tranny Mustang PCM (and has been in the truck for years and years) but since I run a C6 with zero electrical controls, no worries there.
 
Check really carefully for things that may have been accidentally damaged during the hydro install, like sensors on front of engine and maybe coolant temp sensor. I don't really know that engine to know what is located where, but I always look really carefully for the low hanging fruit during troubleshooting.

Have you reset the ECU to see if the problem has to do with short or long term fuel trims that have changed since it was starting without issues? That's farfetched, but can sometimes be a clue to the symptoms.
 
Last edited:
Have your plugs been wet with gas? I've seen a few cars come in the shop lately that won't ever run once the plugs gas foul once til you stick another set in. Used to you could pull them, dry them, set them on fire, then spin the motor over with them out and reinstall and it'd light off, but recently they won't without fresh plugs, I'm thinking it's shitty gas. Might want to stick a set of cheap autolite or champions in it just to see if it cranks.

Also the eec4 fords would do crazy shit with a bad computer ground that usually hooked up by the battery, no ground and they won't run either. That's all I've got, good luck.
 
^im thinking bad gas also, especially after sitting. But I'm curious to hear what it is
 
Jody Treadway said:
That crossed my mind, but I don't like to sit on public toilets to piss. :D
Click to expand...
At least the ls will get us to the public toilet....[emoji12]





But I kid....carry on
 
Back
Top