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454 TBI XL Recommended Spark Plugs and Timing

GAS engine, transmission and generator repair and maintenance discussion forum.
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby 390Express » November 8th, 2018, 8:07 pm

bud37 wrote:Source of the post
390Express wrote:Source of the post It’s my understanding that my distributor is the AC Delco <a href="tel:1104060">1104060</a>, and it’s the same distributor as most of the TBI/MPI distributors for Merc and Crusader, ECU controlled timing).

Plug wires are new this year, routed the same as factory. I was checking the timing in neutral, looking at the time at idle (750), off idle around 1500, then near the full advance mark of 2800. Engine was slowly brought up to RPM and monitored through acceleration to see if it was jumping around a ton. Nothing out of the ordinary, just seemed unusually high at full advance.

Just cause wires are routed factory doesn't mean all is ok,...... I still cant figure how you are getting such high timing numbers on both engines......at idle maybe around 8 btdc and maybe full in around 32, I say maybe because I dont know what the spec actually is. It is possible to get higher numbers with a knock sensor to help control things under acceleration. Something is fishy here.
Do these engines run hot ? What does your mechanic say about the timing , he must have some opinion on those numbers....



The engines don’t run hot. The initial and total advance for the Stb motor were both high by about 10 degrees (checked 18/45, supposed to be 8-34). Changed the plugs today and took 10 degrees of timing out of it. Not much change. Mechanic didn’t offer any reason why the prior initial was set so high, it was that way when I bought the boat, I never messed with it.

Just did a little test. The motor runs fine for 3-5 minutes, then you hear a slight change, and 5 seconds or so later, the check engine soon light comes on, and it runs like hell. I left the check engine soon light on, fires it up again, ran like hell again. Shut it off at the breaker, wait 5 min., start it back up, runs great for 5 min again.

Is there a way to test the knock sensor? It appears to be on the left side of the block, as you’re standing at the front of the motor, right by the fuel pump. Also, is there a way to bypass the knock sensor to test it? (Leave the circuit open, or jump it). Knock sensor appears to connect with a quick disconnect. What’s the proper way to remove it?

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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby 390Express » November 8th, 2018, 11:03 pm

New information. After changing the spark plugs, and taking timing out, I did the above test again. Motor has always ran like hell after the check engine soon light came on, and would never recover. That has changed, somewhat.

Now, after a couple minutes of the check engine soon light coming on, it dies down to around 500rpm, then after about 15-20 seconds, all 4 “idiot lights” (Check Engine, Oil Pressure, Temp, and Trans Temp) come on, and then 3-4 seconds later, they all disappear, and it runs decent again. Not great, but decent.

Secondly, running it at night showed that the wires occasionally arc. Sporadic, but it happens. They’re ran as far away from anything metal as possible, but it still happens. No break in the wires, they seem perfect, just not insulated very well. Brand new wires (Sierra Marine Wires, supposedly a factory replacement). The arcing and the Check Engine/poor performance do not seem to coincide with one another, but it does appear to be an issue.

*** edit to add, the only time I noticed it arcing, is when I adjusted the timing a small amount while it was running. Shouldn’t have anything to do with it, but figured I’d mention it.
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby 390Express » November 9th, 2018, 1:35 am

Something that just popped into my head... going over at the motor could be running worse, now that it’s objectively better:

The RV8C plugs are a colder plug, the recommended seems to be more on the RV9 - RV12 scale. Perhaps now that my octane is closer to 91, than garbage, I need a hotter plug to get a more complete burn, and not foul out the plugs?

I’m 90% certain she’s coming out of the water tomorrow, but distributors, better plug wires, new fuel water separators and fuel filters, and proper spark plugs are on the early agenda for spring.
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby g36 » November 9th, 2018, 6:47 am

I've been hoping you find a solution. Wow sorry your havin to haul the boat. Not being able to find the problem and having to wait till spring would drive me insane it would be all I could think about. Best wishes, hoping for a early spring for you.
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby bud37 » November 9th, 2018, 9:16 am

So , since you now seem to have a repeatable problem, hire a tech with a laptop with the appropriate program and some know how of gm / crusader systems .....you have sensor inputs, the timing module,sensor coil, someone has played with the timing etc...its the only way, there are pages of complicated diagnostics for those things alone, cant keep throwing parts at it........those engines are expensive,........just my two cents man , good luck.
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby 390Express » November 9th, 2018, 10:24 am

bud37 wrote:Source of the post So , since you now seem to have a repeatable problem, hire a tech with a laptop with the appropriate program and some know how of gm / crusader systems .....you have sensor inputs, the timing module,sensor coil, someone has played with the timing etc...its the only way, there are pages of complicated diagnostics for those things alone, cant keep throwing parts at it........those engines are expensive,........just my two cents man , good luck.


Thanks Bud. I had to take care of the known mechanical issues first, as they will give false readings, but I'm getting to the point where I'm near ready to run codes and see what the computer doesn't like about what I have going on. This spring I will change the distributor, install better wires, and install proper plugs. The distributor is varying 4 degrees (+/- 2 degrees) and the manufacturer recommends changing any distributor that varies 2 degrees or more. The current wires are brand new, but they're 7mm junk. I wouldn't have bought them, but installed them because they were brand new and came with the boat. I'd prefer something better insulated, which the boat seems to require, and the plugs definitely seem to be on the cold side.

Those are all known mechanical parts that I know I have to change to be within factory recommended specs. If I'm still having any issues thereafter, I agree with you fully, it's time to get out the diagnostic computer and run it.
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby 390Express » November 9th, 2018, 10:28 am

g36 wrote:Source of the post I've been hoping you find a solution. Wow sorry your havin to haul the boat. Not being able to find the problem and having to wait till spring would drive me insane it would be all I could think about. Best wishes, hoping for a early spring for you.


Ha, thanks G36. I knew what I was getting into when I bought it. I actually purchased the boat under the information and belief that it needed a motor, but later discovered that the port motor was fine. Oddly enough, the motor giving me the most trouble is the motor that was supposed to be good (and was running good for the majority of the summer). The motor that was believed to be bad needed a new ECU. Frustrating to diagnose, but it was nice to correct the problem for $800 and minimal amounts of mechanical effort (4 screws and two connectors), vs $5k and a long weekend project. That said, even if I did replace the motor, there's no guaranty that I wouldn't still be having these issues. Wiring and sensors don't generally come with a new crate motor.

At this point I'm confident that I'll have it running perfect next spring. It's close.
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby 390Express » November 9th, 2018, 3:18 pm

I'm a glutton for punishment...

I couldn't tell last night, but watching it run today, the boat is running really rich. (exhaust out of the STBD side is a lot heavier than the Port) The advice I'm getting online is that TBI itself doesn't get much info from the ECU in terms of fuel output, and if it's running rich, it's probably a clogged injector, or injector screen. Given my prior fuel issues, I'm willing to consider that (despite the fact that the injector cone output looks pretty damn good, honestly). I already pulled the TBI apart, the fuel pressure regulator had rust on one side of it. I'm kind of disappointed, they're not made very well. It was new this year. I understand that I had a little gunk in the fuel, but this side was drained twice, and the fuel in the boat was always good enough to make the boat run. Even in an auto application, the regulator area would get some condensation in it. This probably explains why the prior regulator and spring rusted and collapsed. The other side of the fuel pressure regulator looked perfect, but there was enough garbage on it to make the injector screens rust stained (but they don't look clogged in any way).

Heading to auto parts to pick up two new injectors, TBI rebuild kit, a set of MR43LTS, and new set of 8.5MM wires. I'll at least give it my best shot, and take care of virtually every known issue with the above. (aside from the distributor, but at this point a 2 degree variation in timing seems like the least of my problems) It's coming out of the water this evening or tomorrow. I can do all of the above in about an hour. I've unfortunately became fairly efficient at tearing these things apart and putting them back together.

On a sidenote, Michiganmotorz.com has been awesome. They're willing to "loan" me a TechMate Pro diagnostic tool for $50. I have to pay full price for it, and they'll charge me a $50 restocking fee after I bring it back, knowing that I intend to use it while it is in my possession.

http://www.michiganmotorz.com/techmate- ... -4589.html
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Re: 454 TBI XL Recommended Spark Plugs and Timing

Postby 390Express » November 9th, 2018, 7:30 pm

Well, as my old band teacher used to say: "Better.... but not good."

No more check engine soon faults, the above repairs seemed to help with the boat running rich, but it still stalls after just a couple minutes of running. Now that the faults are clear, it seems like it's losing 12v somewhere, perhaps to the ECU. The weird thing is, prior it would run for 20-30 min. but I had to fight with it. Now there's no fighting with it, it just stalls like someone turned the key off.

Starts and runs perfect, idles perfect, rpms perfect, and stalls, doesn't matter what RPM you're at. Stalled at 900 rpm, thought it just may be cold. Re-started 2-3 more times, same result. Re-started and kicked it up to 2k, still stalled. Re-started and kicked it up to 2,500, still stalled. Nice, controlled stall, no sputtering, no nothing, just like someone turned the key off.

Ignition and ECU power was fine all year. (it was the port motor that gave me most of my issues) It would idle and run under power, no issues. It was running for much longer periods as recently as last week. I'm not sure why it's starting this now, out of the blue. The only differences are that it's been really wet lately, and it's a lot colder than it had been. I haven't done anything since the beginning of the season that messed with the ignition wiring. Gah, looks like I'll be chasing wires this spring.

Any quick tips about easy points of access to check 12v power loss (or ground disruption) at the ecu? I will pull the switch panel at the dash and check the engine off button real quick. It's an obvious culprit and easy enough to rule out.

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