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was it only an issue at the higher RPMs like some have said?
Yes, missing badly under load. The voltage required to jump the spark gap increases with more combustion pressure, and a weak coil will arc internally before the voltage gets high enough to fire the spark plug. At idle the pressure is lower, the voltage is lower, and no problem.
Consider that it's just fine to have an intake valve open while pressurizing the intake. Air gets into a cylinder, so what? Concerns start only when a cylinder has both valves open at the same time.
Yes, missing badly under load. The voltage required to jump the spark gap increases with more combustion pressure, and a weak coil will arc internally before the voltage gets high enough to fire the spark plug. At idle the pressure is lower, the voltage is lower, and no problem.
i would think that this could be an issue, if the spark was weak at idle ,and increased voltage due to the higher RPM and higher alternator output , might fix that. however, with voltage regulators as good as the are, we dont see much in the way of "dimming headlights" at idle anymore. so, you are probably right. strike that off the list, unless someone thinks that a coil 2.5K ohms off spec is soemthing to worry about. two others in my spare parts bin look the same by the way, with 6kohm readings.
Originally Posted by SeanR
Looking at the parts you've pulled off the car, such as the knock sensors, it's obvious those have not been working for a very long time. As noted that fault is going to pull timing from you runs. There is no way that rear knock sensor was going to give you proper readings and was going to default back to it's safety zone. I'd assume the front one was going to do so also. I don't do any racing engines. The one that I build for it was a GT motor that I rebuilt as best that I knew and it's a fine running engine.
But I know sitting on jack stands looking at a timing light is the most rookie mistake one can make. What you've been trying to chase down has been a source of amusement and frustration for some of us who work on these. I don't want to see you fvcuk up that engine the rest of us paid for.
It may very well be that your engine, as good as you feel it runs, has been in the safe area for any engine because it's not actually tuned. I want you to succeed Mark and continue to hold the torch as you see fit. What you may be feeling may just be the fact the idle map sucks, which I've had to fight though with several GT cam equipped 5.0./5.4 cars. You can toss parts at it, but until you have actual data, you are sucking wind.
Like the tires you fought with, you found out your steering rack was the bad portion, not the tires.
Ok, just a few things. the front knock sensor was new, and the rear one was the best of the two that came off the original engine.(cracking, but still looked like a knock sensor) wire insulation was the main issue and i wrapped it in electrical tape because i thought i was going to change it out when the new one came in the mail. (1 was delayed during the engine build)
Next what is wrong with checking the timing with the car on jackstands? i am able to do a solid 4000 to 5000rpm test at pure WOT, with no issues. it is absolutely a good test. same function as any dyno can provide. what is the "rookie mistake " with that? also, this is a great test, because i can test it with the knock sensor attached and with it not attached. to see if the timing is being pulled back 6 degrees.
Keep in mind, i have a stock EZK for an S4 (and i dont know if timing maps are stored there or on the LH) , and JIm C had found that with his GT,tuned for optimization , it ran 23 degrees vs the 29 degrees found in the stock S4.. so, this pulling 6 degrees could have actually been a blessing. keep in mind, this same EVERYTHING on top of the stroker, ran on a stock 5 liter bottom end making 322-335rwhp.. also, Bill did a test that things were all working find, no knocks and things working ok.......and dyno runs, top to bottom have not changed in 10 years. (just did one at the beginning of the season)
I appreciate all the help and concern and dont take what i said above as anything of a dismissal. im concerned/worried and just want to make sure its all running fine for the runoffs. however, if i found that , for some reason, i was losing 6 degrees , would i actually want it back now if the car never had it? after all the discussion, i think i might be a little worried , and rightfully so. maybe, it is in a safe tune , lasted all these years because of it, and is adaquate in the power. sure , an extra 25 to 35hp would be HUGE, but not at the expense of the motor.
your comment about idle maps being bad, is consoling.. maybe thats just it. the fact that it stars up perfect until it starts to o2 hunt, makes me wonder if you are right. its bugging me because it is worse than it has ever been. im thinking its probably some poorly , dribbling out , injector at idle only.
oh, as far as the tires.. it was the tires. maybe even the new suspension being too stiff right now (shocks repaired). the rack was nice to have fixed where my steering angles are 1/2 the movements, but the lap times are still the same. the funny thing is , the car was fastest with everything broken!
thanks for the support and comments!
Mark
Originally Posted by dr bob
Mark--
Consider that it's just fine to have an intake valve open while pressurizing the intake. Air gets into a cylinder, so what? Concerns start only when a cylinder has both valves open at the same time.
can you explain this ? im not picking up the message here.. if i had any valve problem from a float from overrev, that would be the exhaust valve, not an intake, right?
Here is the picture of the spark of a plug grounded to the engine.. this is the spark for both of the distributer caps and coils. i used a spare plug wire to attach a spark plug and ground it , while pulling the injector for that same cylinder. this is the spark i saw on both sides. no noticeable
difference.
can you explain this ? im not picking up the message here.. if i had any valve problem from a float from overrev, that would be the exhaust valve, not an intake, right?
Unlikely you will be over-revving the engine while testing for intake leaks
PLEASE FOLLOW THE DIRECTIONS IN DWAYNE'S INTAKE REFRESH GUIDE. PLEASE AT LEAST READ THAT GUIDE BEFORE ASKING AGAIN.
If I have to spoon-feed it to you, it's gonna be "the hard way" with a big spoon, and it's probably gonna hurt.
Please work some to pick up at least your part of the stuff you are being fed here. Stop arguing about it. Stop questioning the guidance. Just do it.
All this talk on Jeffs engine emissions problem, (too high of Hydrocarbon readings during a smog test) has made me think of a few other things i could check (before i send off the injectors) if Jeffs C0 didnt change , nor did NOX go up , which usually would indicate a lean engine, what if i checked my car .... if the injector is at fault,and not distribting enough fuel............. wouldnt that just be air mixed into the exhaust? doesnt a lean condition change the C0 to be less and the NOX to be higher? And, if it was a miss (where the fuel was unburned, the hydrocarbons would go up, but without the C0 decrease and NOX increase Im thinking if i can get it on an exhaust analyzer, i can see if what im seeing as a cause for a miss is unburned fuel, or not enough fuel or would those have a similar finger print, (considering that not enough fuel would not ignite, So it would have a similar result as fuel that wasnt ignited in proper volume). Thinking out loud here, i think that might only confirm that there is a miss, that is allowing fuel to be unburned, unless for some reason the injector during idle only is NOT opening periodically. in other words, using an example of a condition..........what would pulling an injector do as far as emmissions readings? its not changing the burn mixture, but it is changing the mix of exhaust gas with air as it goes by he 02 sensor, and out the tail pipe.
I've had numerous coil failures here. Age is a bitch.
just to leave no stone un-turned. how did you determine the coil failure?? was it obvious? as you saw, ive measured the basic resistance and im not seeing the characteristic issues at high RPM or loads. only idle.
A friend came by with his McClaren 570. he was idling in the driveway for about 5 mins as we were talking and i noticed he had the near the same miss that I've been tracking for my car. It was slightly less pronounced but a clear miss for sure. I'm beginning to think these cars all make a little miss at idle. maybe nothing is wrong...
Im at the track at the national championships, and the miss is getting a little more pronounced. ill have to put a video of it, but it seems to be narrowing down to the injectors, but it is strange that i cant narrow it down to a single one. its almost stumbling under very light throttle, but still perfect under any kind of load.
anyway, ive always wanted to fine tune the mixture and fuel pressure, by using the injectors more suited for the power i make, so im in search of some flow balanced 928S3 (1985) 24 lbs injectors. Does anyone have a set for sale. then, instead of spending cash and effort on my 30lb'ers which i still dont think is the issue, i can cross that out, AND tune for injectors that will run much higher fuel pressure. (i know, the right way would be to adapt my ECU system to do a shark tune, but i dont think its going to happen)
as a side note, as anyone seen a system where you can remove the fuel rail nut (the one with the ball bearing in it) and the fuel barely leaks out after sitting for 15 mins ? i remember it spraying out and me needing quite a few rags to not have gas go everywhere. that check valve in the pump maybe not working? could that be the issue at idle? ill put a fuel pressure gauge on the system to make sure i sitll have the pressures i started with and that the vacuum is working on the RRFR
thanks for any help in finding some 85 injectors. 24lbers
i don't think you want 85-86 injectors. ""Aren't they different impedance?
Is this right? i thought they were the same impedance. are you sure you are not talking about the euro 85-86 4.7 injectors. those are different for sure.
good question though
Im at the track at the national championships, and the miss is getting a little more pronounced. ill have to put a video of it, but it seems to be narrowing down to the injectors, but it is strange that i cant narrow it down to a single one. its almost stumbling under very light throttle, but still perfect under any kind of load.
anyway, ive always wanted to fine tune the mixture and fuel pressure, by using the injectors more suited for the power i make, so im in search of some flow balanced 928S3 (1985) 24 lbs injectors. Does anyone have a set for sale. then, instead of spending cash and effort on my 30lb'ers which i still dont think is the issue, i can cross that out, AND tune for injectors that will run much higher fuel pressure. (i know, the right way would be to adapt my ECU system to do a shark tune, but i dont think its going to happen)
as a side note, as anyone seen a system where you can remove the fuel rail nut (the one with the ball bearing in it) and the fuel barely leaks out after sitting for 15 mins ? i remember it spraying out and me needing quite a few rags to not have gas go everywhere. that check valve in the pump maybe not working? could that be the issue at idle? ill put a fuel pressure gauge on the system to make sure i sitll have the pressures i started with and that the vacuum is working on the RRFR
thanks for any help in finding some 85 injectors. 24lbers
How fast does the pressure actually deteriorate after pump shut-off? Yes, there's a spec' for that. Likely causes: leaking injectors, leaking regulators, leaking FPR. Is the car hard to hot-restart?
Meanwhile: Buy New Modern Injectors, rather than someone's thirty-five-year-old takeouts. Sharktuning/Sharkplotter will tell you if the current injector sizes are not sufficient for your horsepower, plus tune for whatever injectors you have or choose to install. Going at all leaner at max throttle and max RPM's with what you have? That is the telltale for insufficient fuel flow capability You can probably see that on your WB AFR.
You might remember i had this issue with the Holbert car. didnt effect how it was running, it was said to be a "check valve " on the fuel pump. its since been changed and seemed to always have pressure for 10-15 mins after shut down. this one had no pressure, but doses effect start up at all. remember, i was pulling the fuel rails quite frequently doing the injector test. never has any issues starting, cold, hot or any other time in between. ill put a gauge on it after the runoffs. You can see the AFR meter stay pegged at 12:1 range during WOT at the races.
As far as mixture, no, im very rich at 3000 to 5500rpm and then past 6000rpm, its even richer. so, it goes richer at the higher RPM. Im only at 42psi. my thinking is that the holbert set up ran fantastic at 70psi and i imagine the better atomization is a benefit too. making only 50hp than the previous 19lbs injectors at 70psi, i would think that 55-60psi would serve the HP levels im at today. AND, if there is an injector with a weird idle flow characteristic, that is causing this miss fireing, then that will be gone immediately, unless it is due to something else.
again, remember the engine runs smooth as silk upon start up, and starts quickly with a high starting rev level (characteristic of good pressure) it only starts to miss when it gets a little warmed up.
ive disconnected the o2 sensor to see if going richer during idle would help and it doest have an effect. but then again, i can only assume at idle and 02 sensor disconnected the mixture is richer. . maybe its not. maybe i should hit the WOT micro switch while its idling. is there a way to fatten things up during idle to test that theory?
Originally Posted by dr bob
How fast does the pressure actually deteriorate after pump shut-off? Yes, there's a spec' for that. Likely causes: leaking injectors, leaking regulators, leaking FPR. Is the car hard to hot-restart?
Meanwhile: Buy New Modern Injectors, rather than someone's thirty-five-year-old takeouts. Sharktuning/Sharkplotter will tell you if the current injector sizes are not sufficient for your horsepower, plus tune for whatever injectors you have or choose to install. Going at all leaner at max throttle and max RPM's with what you have? That is the telltale for insufficient fuel flow capability You can probably see that on your WB AFR.
08-31-2018, 12:15 AM
so, you are probably right. strike that off the list, unless someone thinks that a coil 2.5K ohms off spec is soemthing to worry about. two others in my spare parts bin look the same by the way, with 6kohm readings.
