Chasing a slight miss 1998 454

HI Folks,

Need some help / guidance with troubleshooting the following; 1998 XLi 454 Crusader, ~450 hours.

Scenario:

Change all spark plugs (both engines) All gaps set to .042, new distributors and rotor (Delco's).

Both engines fire up fine....

Both engines power up fine but Port has a slight miss / surge / loss of grunt and will rev out to just under 4k but still has a small jump / surge on RPM's......

STB is fine...

So i changed all plug cables...still a problem as per above.

Checked all connections, all fine.

changed back rotor and distributor and the bug is still there....(possibly slightly less) but that could be subjective....

I am thinking either i have a bung spark plug, (or perhaps crossed cables but i will double check that....however i can almost achieve full rpm's,,,,,just not 100% smooth and full power to Port...

NB there were no issues prior to the initial change....no new fuel has been added etc...both engines start as per normal....

Another option i thought of (Pain in the a$$) is to re-fit old sparkplugs to determine if one is no good, or pull each individually and re-check gaps and search for a possible wet plug...

Oil pressure is normal for both engines....changed about 5 hours ago....temp normal....

I cannot think of anything else to add (information wise)

(I am planning on changing fuel filters but do not want to add too many more changes into the mix).

Looking forward to some suggestions..

thanks

Lenny

Re: Chasing a slight miss

Prolly ignition, so i'd do this: at warm idle, i'd pull each spark plug boot off, just one at a time. Note a rpm loss with each plug. The one that drops less than the others is suspect. It is easier with a digital tach.

Re: Chasing a slight miss

UPDATE:

Pulled all plugs and re-gapped.....confirmed correct plug cable assignment....all plugs looked good, dry and clean....

Next stop > try and squeeze down the side (good luck!!) and pull the black flat filter and dump the racor to inspect fuel / water.... I will retest once the flat fuel filter is cleaned then probably swap fuel pumps to see if the issue migrates to STD.....

I did try warm idle and pulling plugs (one at a time) a bit too hard to determine by ear and I unfortunately do not have a digi tach.....there seems to be good spark delivery though....Thanks Diver_dave for your response....

I will update again on this surge problem later on this week when i have done the above items...

Re: Chasing a slight miss

My experience shows that having the engine loaded (in gear) helps the "miss detection" process tremendously on the big blocks. Another approach is to use an inductive timing light on each plug lead to 'detect' a consistent spark.

Bad leads, right out of the box, are not unheard of. I've gotten into the habit of verifying their integrity with the ohm meter test before installing them...a bit labor intensive but can save the misery of trying to find it after installation.

Thanks i am open to all suggestions and (enjoy!) will try everything at least once, it all helps with the learning curve and getting to know the fine art of contortionist's...

Update:

Swapped back distributor, problem is less apparent.
New Racors and cleaned Oberg (hockey puck) filters( they really did not need it, just a small amount of black sediment in each...both engines fired up after twice as normal cranking (prime of new filters)....

Still a slight miss, put back new dizzy and rotor and it was a little more noticeable....

Next stop - swap over distributors and rotors....see if problem still exists....then if so i will replace old spark plugs......last item after that is to check timing......

Does anyone have the details on what the timing should be for my engines...? 1998 XLi 454 Crusader (MPi)

Replaced old spark plugs and problem has gone!!!

two days later engine warning light comes on, idle bouncy...B&G monitor states "Check engine, timing error"....So i will check the timing....

There is a plug on the wiring loom that states it is for timing adjustment....anyone had experience with this...? what tool does it require..?

Update:

My motors actually have a 'Run' and 'timing' plug on them already, and this also lets me 'reset' any errors from the ECU, Once i have reset the the timing and reset the warning i will update...I still suspect there is something more up with this, i am hoping it is not the fuel pump as this will be a real bugger to change out, there is little room down on the port engine (31 Tiara)....

I have also seen some mention about checking the anti siphon valve. I am unable to locate this on my boat, there is no such valve on the tanks, unless it is further along the line (and under the deck)....

Once i get the Rinda software I have fingers crossed that i will be able to better diagnose where / what is causing this issue...

Ok, hooked up the Rinda software tonight...

Port engine is showing an error of "(42) EST System has shorted circuit"....

And i can see on the diagnostics that the spark advance was static....

Any suggestions on what to check for this..?

Some info i have found;

The issue is with the interconnects between the module (4-pin connector) and the ECU. There's a couple of conditions that will set this code. You need to verify which one caused the code and then fix it. send a PM with you email and I'll reply with a service manual extract walking you thru the process, if you want.

So, does the Rinda package meet expectations?

pm sent, i would really appreciate that

Let us know who the "bad guy" was once you have eliminated it

Update: after some exhaustive testing the Ignition Module is the culprit....2 new ones on order. thanks all for your considered thoughts on this

Glad you found the root cause. Once you get the new one in, provide update to verify cause.

Djleny. I believe we have the same engines...TBI?
How did you like the Rinda tool, I was going to get one.

Hi Kimo, no i have MPI,

I am running MEFI 2 though there must have been a transition phase at Cursader around 1998 as the Shop manual i purchased only covers TBI for that year and that version of MEFI...

Rinda tool was a fantastic help in diagnosing the issue, also will be used to snapshot hours and variables every months to be added to maintenance log book etc...

That sounds right. They switched over some where between 97 and 98. My Carver Mariner is a 98 with 97 motors.
Did you have a Malfunction light on your dash?

Sure did, but i started to have a small misfire and funny idle, then the next time we went out the light was staying on, I definately have 98 motors, shame they did not get the MEFI 3. Hoping to put the new igntion modules on this weekend, reset base timing and away we go...just in time for Christmas and New Years