Questions on Misfire for 98 Burb with 7.4l

[Mangonesailor]

I read a test for the dizzy. Pull the cap and see if the Rotor has any side to side play. If it does then it is a sign that it needs a new distributor.

Yes, but the real concern is knife-edging the dizzy drive gear.

Set up a screen on torque for misfires. Put a digital display of the "current" and history" of misfires in a grid as if you're looking down on the engine. See if there's a pattern. Also plot any misfires against the firing order and see if there is a pattern.

Replace that intake gasket then. Don't use a lot of RTV, just a light coat is all you need or the smush that comes out will clog your heater core... also rinse that block out and use green antifreeze.

Refurbished injectors would obviously save you money and they'd likely still back them with a warranty or something.

 

[Frogprince]

So another update.

Pulled the wire. Still have a misfire. Lots of misfire on that cylinder. Doesn't seem to matter the RPM. The higher it does get less.

New development is that I can hear a mechanical clicking noise on that side of the motor. So I pulled the plug again and tested for compression.

If I crank for 4 seconds it is 65 PSI, If Crank for 10 Seconds it is 120 PSI. This is with all plugs in. How long do you need to crank the engine before settling on the compression?

 

[Carlaisle]

That engine is notorious for wearing out distributors. The gears knife edge and the bearings wear out. Replacing it every 100,000 miles or so should be a scheduled maintenance item. That said, a worn distributor would not result in misfires on only one cylinder. That indicates a problem that can be limited to one cylinder, which leaves you with plug, wire, cap/contact, and/or injector. Relatively easy test would be to move the injector. If the problem moves, you have your positive diagnosis. Personally, if those are the factory injectors, you plan to keep the vehicle for a while, and funds are available, I would replace them. They're junk.

You didn't describe the hot start issue. If it starts fine cold every time and after getting to operating temperature you turn it off, wait pretty much any period of time about 10 minutes or more, and it then requires a long crank to get it started you have leaking injectors. They can't be fixed except by replacement. If you replace the injectors, replace that tiny piece of vacuum hose that runs the FPR while you're in there. FPR is probably fine, but can't really test it as long as the injectors are leaking.

Are those compression test numbers and crank times consistent across multiple tests?

 

[Mangonesailor]

That said, a worn distributor would not result in misfires on only one cylinder. That indicates a problem that can be limited to one cylinder, which leaves you with plug, wire, cap/contact, and/or injector.

As far as the likely hood of I only being something on that one cylinder goes, I do not have faith in the black-box's ability to signal if there is an imminent dizzy gear failure. In my own experience, after installing my 0411 and having a case relearn done it immediately detected "random" misfires at idle. After troubleshooting I found my dizzy gear toast.

However, now that he's tanked the wire an there's been no change in the sound of the motor and it's been missing.... obviously he has other issues.

 

[Frogprince]

That engine is notorious for wearing out distributors. The gears knife edge and the bearings wear out. Replacing it every 100,000 miles or so should be a scheduled maintenance item. That said, a worn distributor would not result in misfires on only one cylinder. That indicates a problem that can be limited to one cylinder, which leaves you with plug, wire, cap/contact, and/or injector. Relatively easy test would be to move the injector. If the problem moves, you have your positive diagnosis. Personally, if those are the factory injectors, you plan to keep the vehicle for a while, and funds are available, I would replace them. They're junk.

You didn't describe the hot start issue. If it starts fine cold every time and after getting to operating temperature you turn it off, wait pretty much any period of time about 10 minutes or more, and it then requires a long crank to get it started you have leaking injectors. They can't be fixed except by replacement. If you replace the injectors, replace that tiny piece of vacuum hose that runs the FPR while you're in there. FPR is probably fine, but can't really test it as long as the injectors are leaking.

Are those compression test numbers and crank times consistent across multiple tests?

The hot start is as you described. Frost came about when I replaced the fuel pump and filter. Really annoying to have hot start issues where it takes a few cranks to get going.

The compression is consistent on that cylinder. It seems the others are quicker to get to max.

When I ran it yesterday I did the same on majority of the cylinders. Crank till it stops moving, write down the number and move on. That is how I have always done compression checks.

I am planning on keeping this truck for awhile. The difference on the injectors from 50 is black bosh new and the yellow tops. Price is about 60 bucks more for the new.

 

[Carlaisle]

An IR temp gun on the appropriate exhaust ports could help confirm/refute if cylinder 3 is really misfiring as much as the computer says.

If cost is a concern on the injectors, you might pay a visit to a Mustang forum, eBay, or another market of your choice and see if there are any take outs available. The injectors in Ford's 4.6 of the same vintage as your engine are a drop in replacement and require no tuning. You can often find a complete set delivered for well under $100. I've run a set for years with no complaints.

 

[Frogprince]

An IR temp gun on the appropriate exhaust ports could help confirm/refute if cylinder 3 is really misfiring as much as the computer says.

If cost is a concern on the injectors, you might pay a visit to a Mustang forum, eBay, or another market of your choice and see if there are any take outs available. The injectors in Ford's 4.6 of the same vintage as your engine are a drop in replacement and require no tuning. You can often find a complete set delivered for well under $100. I've run a set for years with no complaints.

When it comes to price. I rather pay out the nose once and have a reliable vehicle. I use this as our off road rig, camping and hunting vehicle. So rather it not break down 100s of miles from the house.

I am looking at the two options still.

There is the new
https://www.fiveomotorsport.com/bosch-oem-454-j-code-884-black-knight/

And the rebuilt
https://www.fiveomotorsport.com/lucas-01d062b-74l-j-code/


Also there is the risk of eBay but
https://www.ebay.com/itm/Suburban-S...788025&hash=item2d0b8e0cef:g:xTYAAOSwHMJYGy-Y




Just not sure which one to go with.

On the dizzy I would expect it to have more then just the P0303 code. Since it is just the one cylinder it leads me to rule down to either the injector or a damaged valve. I lean towarsds an injector due to it having good compression if turned over for 10 seconds.

I have two options. 1) I take it to another shop and pay them to diag it again. See if they come back with a bad head, and if so have them do injectors and the headwork.

2) I assume the head is good. Buy the injectors myself and give it a weekend to put the parts in.

 

[Mangonesailor]

You could put the engine at TDC compression stroke on #3 and then hook your air compressor up and blow 90-120psi in it and listen for leaks in the exhaust/intake and look for coolant bubbles I suppose.

And, on the injectors, I bought a used set of LS1 on eBay and even had witchunter clean them and bench flow them. About a week after putting them in one stuck open (one that was previously clogged shut) and damn near roasted my engine.

If I were you and you were going to buy used eBay sets then buy extra and have witchunter do them. Toss any that were previously clogged/stuck.

 

[Frogprince]

Well I have had it back at the mechanic since I had a friend tell me that it sounded like it was a valve issue (either sticking or damaged).

Two weeks later the mechanic is telling me it would be a waste of money to rebuild the upper end since the motor has 200k on it. He was telling me that they looked at the lower crank bearings and they are iffy and really should drop money on a long block.

They said the BBC 454 is known issue on this and they rarely make it over 250k without needing a rebuild. He was quoting something close to 4k to swap the motor.

Thoughts? It feels like this is a snowball that keeps growing when I sign off on the repair to be told it really needs more.

 

[LC2NLS6]

My 93 454 has 311,000 miles. I just did a compression test, slapped Holley Sniper EFI, cam and intake. Runs great. No smoke, doesn't leak enough to drip on the ground yet.