TBI 454 Misfire

[Rock Hard Concrete]

No light show, but the engine was still kinda warm from earlier so I'll check again when its dead cold. Some more context for those interested:

Bought truck 2 years ago. I put a new cap, rotor, plugs, wires and fuel filter when I first got the truck. Not because of any issues, but just as preventative maintenance since the truck was new to me and the maintenance was unknown.

After a few months, it started having intermittent stalling issues. I replaced the icm but no change, so instead of shotgunning I took it to shop #1 to fix, they said it was cracked pickup coil in the distrubutor. They replaced the distrubutor and new plugs/wires.

After a myriad of issues with this shop, lots of downtime, and paying them a disgusting amount of money, they started ghosting me. Every time I mentioned the misfire they refused to acknowledge the misfire and said my truck was running as good as it did the day it was new. They also contradicted themselves by stating I was unreasonable in thinking a 30 year old truck could run right. "Its just old".

Fast forward to shop #2, they replace the cap, rotor, icm and wires/plugs again, which got rid of the jumping tachometer but not the misfire. They also did the temp sensors and I think the 02 sensor. They too seem to think that the truck is too old to expect to run right and they no longer want to work on it. What a load of bs.

Oh, and both shops seem to think that I am an idiot for thinking an online forum will help; according to them none of you are trustworthy or have any experience. Whenever I reference this forum they scoff and look down on me.

 

[Schurkey]

Remove the distributor cap and rotor that have been replaced 3X, and look at the magnet on the distributor shaft.

Good chance the magnet is cracked. That was the misfire on my '88 K1500 5.7L. USUALLY the magnets crack where the rivet goes through.

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The "fix" is to replace the distributor mainshaft, which at this point in time pretty-much means replacing the distributor, since the mainshafts have been discontinued.

Most "new" distributors come with crappy modules, caps, and rotors installed. Don't throw yours away.
Never mind. That's already been done.

Beyond that...verify fuel pressure, (the fuel pump does not set the fuel pressure. The fuel pressure regulator sets the pressure as long as the fuel volume isn't so high that the return plumbing is overloaded) assure that the spark plugs aren't fouled, the PCV and EGR are working appropriately. Then connect a scan tool to verify EVERY sensor and computer output including electronic spark advance. Check fuel trims. Add a timing light, and verify base ignition timing.

Just for giggles...what is the battery voltage with no load? What is the charging voltage with the high-beam headlights on, and the HVAC blower on high?

 

[Rock Hard Concrete]

Beyond that...verify fuel pressure, (the fuel pump does not set the fuel pressure. The fuel pressure regulator sets the pressure as long as the fuel volume isn't so high that the return plumbing is overloaded) assure that the spark plugs aren't fouled, the PCV and EGR are working appropriately. Then connect a scan tool to verify EVERY sensor and computer output including electronic spark advance. Check fuel trims. Add a timing light, and verify base ignition timing.

The distrubutor itself was replaced, for that exact reason. PCV works well. Timing was supposedly set at 6 degrees with timing wire unplugged but I will verify soon. Knowing my luck and the way the shops hate this truck, I do not think a scan tool will do any good but I will check and see if there are any loaners from a part store.

 

[Rock Hard Concrete]

I just want to add that I am 27 grand into this truck. I have paid to fix it multiple times so if I come across as abrasive its just because this thing has crushed my spirit for 2 years.

 

[Rock Hard Concrete]

Just for giggles...what is the battery voltage with no load? What is the charging voltage with the high-beam headlights on, and the HVAC blower on high?

Thank you for mentioning that! I totally forgot, the original battery froze solid shortly after buying the truck, so I got a new deep cycle AGM battery and new alternator. The voltage has never been great, 14 volts cold with no load then drops to about 12-13 after warm, and less when the lights are on. You can even see the voltage drop when the turn signal goes on and off.

*Edit* there was a weird one-time electrical issue shortly after replacing the battery and alternator. The truck lost all charge from the battery overnight like the lights were on (they werent). This only happened once.

 

[Carlaisle]

Turn signals alone should not cause a visible voltage drop. You are likely missing some body/engine/frame/battery grounds or they are corroded and need cleaned up. In the process of checking them, you would be well-served to upgrade them, as well. Little cost in labor and materials for an outsized increase in performance.

 

[tayto]

the turn signal thing is a common GM
flaw, my squarebody does it, my caprice does it, early gmt400s do it.

i usually use the TPI pump as a replacement, but I've never had an issue with it overwhelming the stock FPR. usually the vehicle runs noticeably better after swapping pumps. while this could be a combination of the TBI pump being worm, it has been a common swap for 20+ years.

 

[Sean Buick 76]

Use a timing light to verify if each plug wire is getting spark consistently.

 

[Schurkey]

Use a timing light to verify if each plug wire is getting spark consistently.

Yeah, that can work. It doesn't work well, however.

A proper spark tester, calibrated for HEI is FAR better, as it forces the spark to actually jump a calibrated gap. If the spark can't jump the gap consistently, the ignition system has issues.

There's many styles of spark-tester; any of them that involve lighting-up a lightbulb are not worth the effort. My preferred style:
www.amazon.com/dp/B003WZXAWK/?coliid=I3S98D7T1J0RLJ&colid=2VLYZKC3HBBDO&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it

 

[Rock Hard Concrete]

Turn signals alone should not cause a visible voltage drop. You are likely missing some body/engine/frame/battery grounds or they are corroded and need cleaned up. In the process of checking them, you would be well-served to upgrade them, as well. Little cost in labor and materials for an outsized increase in performance.

All engine compartment grounds have been cleaned, replaced and I added extra just so that engine grounds will not be the issue. Are there grounds in the cab that are serviceable without destroying the dashboard? My headlights do take a couple of seconds to come on after pressing the switch and the dash lights take a few more seconds to come on after the headlights do.