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flammewerfer · 05-21-2024, 10:07 AM

I have a '93 Thor motorhome on a Chevy P30 chassis, with a 454 V8 labeled Tonawanda on the valve covers. I believe the model is a Four Winds 340 (34 foot), if that helps. I inherited it from my dad and it has a few... maintenance issues. The engine starts and runs like a champ for the most part, except under heavy load, mainly pulling itself up a hill. If you're a passenger, it feels like the driver keeps letting off the gas and then hitting it again, cutting in and out.

I decided to try a tune up to see if it would help, and discovered that although someone labeled the wires they're labeled wrong (they have numbers 1 through 8 which do not correspond to the cylinder the wire is actually hooked up to) and, more importantly, after tracing the wires and sussing it all out the actual firing order looks wrong.

Every diagram I've seen says the firing order should be 1-8-4-3-6-5-7-2. Unless I'm reading the diagram or tracing the wires wrong, the actual firing order is 3-8-4-5-6-7-1-2.

Three questions:
First, should the engine run with this firing order at all? The reason I ask is because I'm scratching my head over this, wondering if someone did it on purpose, e.g. if this engine has a different firing order than the diagrams I've seen online.

Second, would it be safe to swap the plugs around to what the diagrams say and try it? I don't want to blow it up.

Third, they mostly ran the wires in the OE plastic holders, but they also zip tied them into two tight bundles near the distributor, one going to either side of the engine. With all the wires jammed together like that, I've heard you can get crossfire conditions, and I'm starting to wonder if that's the only reason this beast runs. Or maybe another possible source of my problems.

I'm somewhat handy, but haven't dealt with something like this before, so I wanted to check with some experts before I mess with it. Thanks!

TonyMac · 05-21-2024, 10:23 AM

The firing sequence can be modified for increased ride comfort. The 4/7 cam swap changes the firing order to 1-8-7-3-6-5-4-2, improving engine smoothness. However, the firing order always starts with 1. 1-8-4-3-6-5-7-2 is a song most Chevy guys can sing in their sleep. With your firing order of 1-2-3-8-4-5-6-7, it should not run at all, you're way too far off. And sequencial cylinders firing sequencially would bake a shaker out of that engine. I think you traced it wrong.

Next, it's the order of the wires, not the plugs. The plugs can go in any cylinder, the wires must go from the correct point on the distributor to the correct cylinder. The #1 cylinder is the most forward; in the 454 it's on the driver's side, and #2 is on the passenger's side. Where the #1 wire connects to the distributor can fluctuate with install errors on said distributor.

While your messing wit the wires, why not ohm them out or just replace them altogether. 30 yo wires could be your problem

Skip426 · 05-21-2024, 11:00 AM

Tony , has detailed the info .

Firing order 18436572 ; #1 , drivers side front of the engine .Odd #s on drivers side even on passenger side ; same as Chrysler V-8s ( Ford just had to be different

)

As Tony mentioned , if someone had the distributor out and replaced it without indexing the rotor to #1 cylinder TDC ( Top Dead Center ) and just installed the plug wires to the unindexed rotor position ; that could be the issue .

Anyhow , could you post a photo of the name on the valve cover

I'm interested to see and figure out what's going on there .

flammewerfer · 05-21-2024, 11:19 AM

Fair enough on the possibility have having traced it out wrong! I'm heading out to lunch with my wife for her birthday, but I will verify it as soon as I can.

Apologies if I used terminology wrong. I meant "plug" as in the cylinder the plug is in. Your description matches the diagram I was going off of. Since half the engine is definitely right, I think the distributor was installed correctly, most likely. Definitely going to trace out that other side for a third time. I traced it twice, but that doesn't mean I didn't make the same mistake twice.

The wires have been replaced at least once, but yes, putting new ones on is definitely the plan!

Thank you for responding!

flammewerfer · 05-21-2024, 01:02 PM

Hey guys, just got home and did a quick check. You were entirely right, once I knew what to look for I spotted it. There was a tough-to-see spot between two of the holders and the top wire had some extra length, so they ended up putting it in the bottom spot and moving all the other wires up a slot in the holder. I didn't notice, so I thought they were off. Thanks for catching that, TonyMac.

Skip426, I forgot to take a pic of the label on the valve cover, but this is what it looks like. Apparently it was just the location it was manufactured, otherwise it's the same Chevy 454. I'd be happy to clean it off a bit and post a pic of the actual one if you still want.

So, my plan is to do plugs, wires, rotor, and cap. Then see how it runs. Any other suggestions for the behavior I mentioned? I saw something about a malfunctioning transmission temperature sensor being able to cause misbehavior, but I don't know how to even begin diagnosing whether that's the cause.

77Travco · 05-21-2024, 01:08 PM

Could be a weak fuel pump or faulty pressure regulator.
Replace fuel filter. There should be one somewhere on the frame rail.
Check the air filter.

twinboat · 05-21-2024, 01:21 PM

The surging under load points to a plugged fuel filter. Change that.

1972VWbus · 05-21-2024, 04:36 PM

The 93 will have 9-13psi for fuel pressure. To check the fuel pressure you'll need a GM pressure kit...https://www.harborfreight.com/basic-...kit-64939.html

Change the fuel filter is a must.

I would also pull the distributor and replace the pick up coil and check the magnetic stator to make sure it has no cracks in it. When you pull the distributor make sure it is at TDC for #1 prior to pulling or take a pick of the distributor straight down prior to pulling. Take notice when lifting it the rotor will turn slightly. The point at which the rotor is pointing 'once free' is where it should be when reinserting. Once seated it should be where you took your pic of it prior to removing.

Also helps greatly to get an OBD-1 phone app with bluetooth capability so you can see engine data in real time. Go here for that...https://www.youtube.com/@Electronics-bd3er/videos

flammewerfer · 05-21-2024, 05:44 PM

Fantastic suggestions here, guys. Some stuff I didn't even know about, like the pickup coil and magnetic stator, I will be doing some online learning so I know what I'm looking for. Fuel pressure regulator is something I didn't think to check either. Definitely going to put a fuel pressure gauge on it.

The OBD-I reader is a great idea if none of this does the trick, thank you for the tip!

Thanks for all the great help, you guys are amazing.

Skip426 · 05-22-2024, 09:12 AM

The decal photo is fine ; thanks for that .

But the fact that the engine has the decal , leads to the question ; was the engine modified ( high torque camshaft installed ?) either by the coach builder or a previous owner .

1972VWbus · 05-23-2024, 01:25 AM

Quote:

Originally Posted by flammewerfer

Fantastic suggestions here, guys. Some stuff I didn't even know about, like the pickup coil and magnetic stator, I will be doing some online learning so I know what I'm looking for. Fuel pressure regulator is something I didn't think to check either. Definitely going to put a fuel pressure gauge on it.

The OBD-I reader is a great idea if none of this does the trick, thank you for the tip!

Thanks for all the great help, you guys are amazing.

When testing the fuel pressure be sure it is closer t 13 than 9. You'll have issues under load if it isn't closer or at 13psi under load or WOT.

And for rebuilding the TBI you can take a look at the following thread when I did mine...https://www.gmt400.com/threads/454-t.../#post-1321339

You can see the fuel pressure tester adapter that I installed on the inlet port of the TBI.

D Gardiner · 05-25-2024, 08:29 PM

When we got our 1996 454 out of mothballs from my parents, she fired right up.
However, the 5 year old fuel (with Stabile in the tank) did not like full throttle. It bucked, coughed, and spit. It took about three tank fulls of fresh fuel to get her to run right.
We changed plugs, wires, filter, did an oil change etcetera. Until all of the old fuel was completely diluted she still hated full throttle. It took about 2 months and an over 1000 miles to get her to run perfect.
Have patience. And congratulations on your rig.