Rx7 fc

Rx7 fc 1986 s4 / na
I'm not sure what caused this exactly but, 87 octane, 1/2oz per gallon pre mix, fouled plugs, thinned out gas smelling oil going on I was getting pinging at high rpm.

I just changed plugs and oil after work and the plugs needed a good change one of them the cross was completely full of carbon. I believe it was leading plug front rotor. The oil smelled of gas and was a bit too thin for my liking.

I don't know what attributed to causing it to ping, but in high rpm and letting off throttle it would ping. Switched to high octane gas and the pinging wasn't as bad/ minimal. Changed plugs and oil and seems to have completely gone away. Now I'll have to try 87oct gas again to see if it bothers it or not.

I know that pre mixing lowers octane rating, now that our gas also has ethonal in it could pre mixing be causing drastic swings in octane rating? I'll test out switching octane up, but currently 92+ pre mix is giving me a great power feel in mid rpm range too. Plugs worked wonders.

One other note, the pinging only started after I switched to a high flow exhaust and before plugs and oil change.

R_PROWESS

iTrader: (3)

Need a bit more information here. Is this even a turbocharged engine you're talking about? Fuel diluted oil is pretty normal.. are you doing regular oil changes? It would take far more premix than you are running to effect octane of the fuel and I'm pretty sure the amounts I'm talking would actually increase octane.. not reduce.. as it would be harder to ignite the fuel.

j9fd3s

iTrader: (3)

i had an S4 NA and with the timing advanced a few degrees it would ping a little in the midrange on a really cold night, on 87. kind of why you have to be careful tuning anything

also, and this seems likely, that if there was enough carbon to fill the plug, it could have been hot enough to cause your pinging too.

there are other things too, like the condition and routing of the spark plug wires. if you search for "inductive crossfire" you will find that it blows up engines

Rx7 fc

It's an 86 s4 / na, how often do you guys do oil changes? The oil was rather thinned out by gas more than I'd like.

I'm not sure if the timing has been messed with at a prior point. I'll have to check timing next, the plugs also were causing issues. Cross talk between wires is interesting I hadn't thought of that. Plug wires need to be changed, super old still working though. Rats might have nibbled on a plug wire or two, I can grab them with no shock but not the best looking things.

​​This car sat for a long time (years) and had some mice visit. It's taken a lot to clean up and the usual things like belts, hoses, coolant, just did oil change and plugs. I only drove it a little since I've gotten it because I knew the oil was bad, hindsight maybe should have changed that day 1.

Next need to flush diff and I guess theres oil in the shift linkage area?

j9fd3s

iTrader: (3)

i like to do 2000-2500miles, or a year, whichever happens first. if you do long trips, you can go further, the engine actually isn't very picky about oil, as long as there is some.

ideally you want to either separate the wires as much as possible, and or cross them at 90 degree angles. if you cross them at 90 degrees, this cancels the magnetic field.

scathcart

How confident are you that what you heard was detonation?

The reason I ask is high rpm and letting off the gas puts the ECU into decel fuel cut. with no fuel being injected, how would you detonate?

Rx7 fc

Sounded like a chain rattling in the engine or a failing bearing type sound, I initially thought it was a belt but my buddy and I tested it out and was for sure coming from the block.

Matched a video I watched documenting ping in rotary as well same sound. High pitched ringing might be another way to describe it.

scathcart

were you in full decel? Like i said: high rpms, throttle closed means the fuel injectors aren’t firing. No fuel= no detonation. You normally get pinging around peak torque or while lugging the engine around by flooring it in too low a gear with two much ignition advance dialed in.
have you checked your TPS?

Rx7 fc

These cars are ancient tech how do you check tps? I check all my odb 2 ones because easy..

I guess it was maybe ocuring at peak throttle engagement, just seemed to continue for a second after let off. It's not doing it anymore after plugs and oil that I've heard yet, but also minimal testing since I've done anything. Too cold out.

scathcart

Digital and analog multi-meter probing at both the TPS pins and at the ECU.

High rpm knock would also be odd, especially on a stock ECU.
At that point, I’d look at the spark plug wire quality, and how they are routed.... it’d be rare for a non-turbo care, but you maybe could be getting some inductive crossfire.

Actually, more importantly, make sure all the spark plug leads go to the right plugs. Leading is the lower plugs, and the forward most coil in the engine bay. Usually black lead ends, and it doesn’t matter which wire goes to which plug because of wastefire. Trailing is top plugs, rearmost coil by the brake booster, usually blue lead ends, and it definitely matters which wore goes to which.

docbong85

Just a side note here, don't know about where you're at but here in Canada 87octane has up to 15% ethanol in it. Unless your motor is built for it with upgraded seals and such ethanol will eat your rubber seals. Water jackets especially. Just bought an 87 FC with a motor that was toasted this way. 91 or better in these cars unless you've rebuilt with something like Goopy seals.

FührerTüner

iTrader: (5)

Verified fuel filter is good and fuel pump is in good working condition?

livingroom computer

this is my other account. yeah I checked out the fuel pump and pressure is good,I have not changed the fuel filter im sure it needs it. is the stock fuel pump discontinued? I have an idea for also relocating the fuel filter as the location is garbage not super accessible. I ordered new ngk plug wires and wow the quality of ngk wires is really great. havent got a chance to install them yet. I spent this weekend pressure testing my transmission on my truck and changing a radiator and rebuilding cooling system on another car I need to have up and running.

I will probably switch to higher octane fuel because of the stupid *** ethanol content issues. car runs great on higher octane fuel also (I read people used to get lower power from higher octane gas) I have no power losses though.

rxtasy3

iTrader: (2)

why did u make a 2nd account? if it's a password issue, message a mod or admin to resolve it.

FührerTüner

iTrader: (5)

I had a similar problem with lean AFRs and it ended up being my fuel filter. It was too dirty to handle the flow for up top. Check your fuel pump sock as well.