mark kibort

Hey, I just put the new plugs in and went on a rampage of WOT to bed the brakes. (race brakes are a little stubborn ) in doing so, when i started up the car. the car had a very odd ,and uncharacteristic "miss". kind of sounds like.......paaaaaaapapaaaaaaaaaaaaaapaaaaaaaa. 60-100mph was the best I've recorded, in the 4.3 second range and is smooth as silk. I did have the LH box disconnected for the compression test, so that might have reset the computer. but , it still did it after about 1 hour of driving. i replaced the plug wires 5-6 years ago and there was a problem with the #4 plug wire so that is still original, and looks pretty beat up. move it away from the cam covers and there is no difference. looked at the engine running at night and no visible arcing.............remember when i had this issue that effected it running, it was a visible arcing of the coil terminal.that doesnt seem to be the issue. any thoughts?

mark kibort

i just found out why the coil wire fell out at Auto Club speedway.. the connector on the wire broke in the coil itself, in half! so, the only thing that was holding it in the coil was the rubber boot. guess the spark was powerfull enough to jump. no surprise there, but i thought that woudl be the cause of the miss... not the case.. I dug out the stuck broken piece , replaced with new coil wire and it is still missing in the idle , low RPM range. changed out the one plug wire that was old (very old) because when i changed the set, there was a wire missing .... another story. #4.... anyway, took an old plug wire i had laying around and changed it, and it didnt change anything.. the cap and rotors look ok. some build up on the contacts, so its been about 5 years or so since ive changed them, so ill replace them with new and see if that works. any other thougths?. it certainly sounds electrical /spark.

mark kibort

Here is the cap and the coil wires. the one on the left is the broken one, the right is the new one, with the cap on top cap looks ok, but it is 5-6 years old, so out it goes

Ducman82

that will do it! :-)

mark kibort

but, it didnt still the same miss. so,, maybe the new caps and rotors will solve the problem.. otherwise, what could it be?? what to look at next? wires are new now, plugs are new , cap and rotor will be...... so whats next. could it be the coils?

FredR

Mark,

Fit your new cap and rotors and then report back. It will be interesting to see whether you notice an improvement.

I get the impression your policy regarding preventative maintenance is to replace the oil every race and anything else every 20 years or so!

If you are going up against the kind of chaps you are currently playing with you need everything possible working in your favour otherwise it is just a waste of time and effort if after a couple of laps you end up coasting into the pits as seems to have happened last couple of times out due to tyres being knackered or spark leads falling out. Appreciate such approach costs but you really need to ensure that simple things do not wreck your day out if you spend 7 hours driving to a track, fuel/expenses for your tow vehicle and feed/entertain the family etc etc. In this regard you really need a well thought out plan about when to preemptively change components out and/or have specific parts rebuilt. At the end of the day 1 component failure can and invariably will spoil your day out.

Every component in your 928 has a MTBF [mean time between failure]- unfortunately we are not privvy to such info but I dare say the list could generate a schedule of what to replace and [more importantly] when to enhance reliability. I have my own basic list of what to replace and when, usually time related in my case as I do not cover many miles..

mark kibort

yes, i had a MTBF guess for most of the "consumables" the plugs were every year as were the caps and rotors every two years. timing belt was every 5, or when the water pump blew up or started making noise. shocks and springs, i made the mistake that they could last forever and might give signs that they were going bad.. (seepage, etc) definitely wrong there. tires, is a crap shoot. the new compounds of Hoosier, dont seem to age as well, so used , even if my own, are junk after 8 heat cycles. that coil wire falling out, was the connector inside breaking in half. the new wires seemed to have a coil wire that didnt look as robust at the stock 928 original, so i left it in there. didnt think that the core would break. however, that race at Auto club was a bonus. i didnt want to reall race the last race, as i needed to get back home, so no loss. actually, it was good. all these failures help fix issues before a more important race.

So, when you compare my program with the "others" at the track... i still have a LOT less issues than man of my competitors. that shop i took the picture in front of.... did you see the picture of the vet with the bodies under it???? wrenching for 2 days trying to get transmission leaks fixed. they have had All sorts of issues , almost every weekend. the owner of the shop, blew a clutch, and was out after 5 laps. a $100,000k car, that runs near the same times as me and he is going to the nationals....blew a motor at the last nationals after having the lead for 4-5 laps until.........boom! ) the list goes on and on.

the point is, have a budget........and over years, im a little lax on changing things out, just to change them. i keep an eye on stuff, but things do break. sure, if i had an unlimited budget, i would replace every rubber bushing, every rubber hose , every relay, switch and wire in the car.... and maybe now.. pull the engine for a rebuild.after all, its been 120 hours of racing and 30,000miles of street driving.........but i dont have that kind of cash. im a one man show, and i pick and choose my battles. ive had a lot of failures that have not ended the day.... wheel bearings in the rear, water pumps, and i have had others that have made finishing harder, like . power steering line, and overheat (water pump, fail to bleed system before race). and yes, tires.. so, this season, i did make an effort to buy new tires for the seasons most important race and only use used tires that were 4 heat cycle old from known racers. it seems to be helping. i think much of my handling issues is that the car has a broken set of front shocks, so it will be good to see how they help at laguna at the end of the month

You have to race to understand that most of the fun is competing and pushing you and the car to the limit. the classes are not fair by any stretch, so if you want to win, you are deluding yourself, unless you have a near unlimited budget. the guys up front are cup cars 2016 GT3 991-1, or an ex world challenge GT car, or a custom built $300,000 turbo charged NSX. so, you find your spot, have your wheel to wheel race, , among the fast guys, and be proud that you can beat half the field of much newer and/or,more expensive cars and teams. you need a top car and new tires to be in the front, and that means 2-3000 dollars in tires every weekend. if you dont sign for that. you dont get to the front.

anyway, i am not hopeful that the new cap and rotor will fix the issue, but the issue seems not to effect HP and how it runs at WOT at the track. only the idle. but i dont like things that dont work perfectly, and a small issue now, might be a big one later, so i want to figure it out. i also bought a brand new wired for that #4 cylinder. the replacement was used , and didnt change anything.. ...... so, it sounds electrical...................maybe the coils?

mark kibort

Has anyone found a miss with their car's engine, that was solved? if so, what was the cause. im beginning to think ill never find it. does anyone think that the miss being no problem at high RPM (full load) masks it or cures it due to the higher voltage of the ignition system at high RPM? could a bad knock sensor be pulling timing out, causing a miss. (i remember when we used to time cars by the distributor cap rotation and it would start to miss when retarded) I never replaced that old knock sensor at the rear of the engine as it was on back-order when i built the engine up. ive got it , new in box, and just need to install it. anything else i could chase?

dr bob

Mark --

Check the compression. Stupid stuff. It's always stupid stuff. But the engine has a few essential requirements that include compression.

Got access to an oscilloscope? Amazing tools. Wrap a short piece of wire around the coil wire and the trigger around plug 1 wire. Look at the height of the traces. All the same? If not, find out why. Swap to the other coil wire and look at the other four cylinders.

Get one of those listening things for the injectors. Use it.


Problems that happen "only at idle" start with mechanical conditions that affect dynamic compression at low speeds. Leaking valves, damaged piston, flattened cams, collapsed lifters all fall into this category.


The rear knock sensor won't cause a miss at idle. It will retard timing, which affects power across the RPM range.

mark kibort

Well, i found it. dont know if it is due to the caps or rotors, but changing them out and it runs like a champ now.. smooth as silk at idle.

its been a long time since ive replaced everything, but now its got plugs, caps and rotors and the plug wires are near new. maybe there will be some lost power found too. compression checked out find too.. so, hopefully, it will run strong for laguna in 2 weeks after the new shocks are installed. and be ready for the SCCA Runoofs!

thanks for the suggestions!

Mk

jpitman2

I had a miss cold once on electronic ignition car, and eventually I found 1 magnet in the rotor that was firing the reluctor was a little weak - closing the gap at the reluctor/rotor from .014 to .012 fixed the problem....Lucas of course.
jp 83 Euro S AT 57k

mark kibort

I dont know where my weak link was, but it was a remarkable change . actually fixed! maybe the resistance just was too high, and was effecting idle spark due to the spark level, and seemed to be not an issue , when RPM was much higher during WOT racing operation, so im wondering if it was just an idle issue (low RPM) but might have gotten worse with time. anyway, its solved and the engine sounds happy.

rjtw

Mark, where n when is the next race? I'll get it on calendar!!

mark kibort

Laguna seca .... saturday June 28th probably around 11am

mark kibort

just let the car warm up and the miss has returned. i havent had a chance to drive it due to the suspension being rebuilt, so i took it out for a spin today. as it warmed up in the driveway, it started the same miss. no change. interesting that it seemed to be find when it was cold.. .........oh well. back to the drawing board! any ideas????????????????????????????
new cap , new rotors, replaced the only plug wire that was not new from a few years ago... replaced a bad coil wire ,and now, the miss persists!!!! compression pretty equal for all 8 cylinders.. new plugs too. UGGGGGGGG!!
i guess the only thing left is fuel? all the injectors are clicking away, loud on the stethascope. but if one is clogged , i guess that could be an issue, but i have a hard time believing that could be it.
idle is misses pretty bad... part throttle 3000rpm , still missing in idle, however, under load there is no miss at 3000rpm or higher. accelerates hard to redline, no issues and seems to have full power.

great... just spent $300bucks on stuff that was probably just fine but the bad coil wire which i had!

any ideas?


thanks!