rpm specific fuel cut
#31
Drifting
If there's a local college in your area that has an automotive shop and a Dino you might be able to talk to the instructor into putting your car on the Dino for a load test and you could check out the fuel pressure. Or get a hose with the correct fittings on the ends, run it up to the windshield wipers and connect the fuel gauge there for a quick one time test run. but I would seriously replace your ignition wires first. You may just have an awesome light show going on under your hood.
#32
If there's a local college in your area that has an automotive shop and a Dino you might be able to talk to the instructor into putting your car on the Dino for a load test and you could check out the fuel pressure. Or get a hose with the correct fittings on the ends, run it up to the windshield wipers and connect the fuel gauge there for a quick one time test run. but I would seriously replace your ignition wires first. You may just have an awesome light show going on under your hood.
#33
Burning Brakes
Here's a quick test for the fuel system. Get a hand pump with a 50psi gauge, attach it to the fuel pressure regulator line, add a jumper line to the fuel pump so it's running with the car off, then slowly add pressure to the afpr and watch both fuel pressure gauge and the air pump gauge. Make sure they both rise at the same rate. If the fuel pump is getting weak it might not handle higher pressure, the fuel pressure might start to drop off as boost pressure goes up. A good fuel pump should be able to produce 63psi, which is enough for 43 psi (3 BAR) base pressure plus 20psi of boost.
I have a feeling your old plug wires were bad. Your symptoms point to spark blowout. I personally don't like Magnecore wires on this car. I tried a set since they worked very well on my other car, but the problem is the boots on the plugs are weak and difficult to remove. After a few remove/install sessions the boots ripped and the wires separated from the crimp terminals. I'm using NGK wires now and they're been great.
Also, make sure your plugs are gapped to .026" to .032" Anything bigger might misfire under boost.
I have a feeling your old plug wires were bad. Your symptoms point to spark blowout. I personally don't like Magnecore wires on this car. I tried a set since they worked very well on my other car, but the problem is the boots on the plugs are weak and difficult to remove. After a few remove/install sessions the boots ripped and the wires separated from the crimp terminals. I'm using NGK wires now and they're been great.
Also, make sure your plugs are gapped to .026" to .032" Anything bigger might misfire under boost.
#34
Here's a quick test for the fuel system. Get a hand pump with a 50psi gauge, attach it to the fuel pressure regulator line, add a jumper line to the fuel pump so it's running with the car off, then slowly add pressure to the afpr and watch both fuel pressure gauge and the air pump gauge. Make sure they both rise at the same rate. If the fuel pump is getting weak it might not handle higher pressure, the fuel pressure might start to drop off as boost pressure goes up. A good fuel pump should be able to produce 63psi, which is enough for 43 psi (3 BAR) base pressure plus 20psi of boost.
I have a feeling your old plug wires were bad. Your symptoms point to spark blowout. I personally don't like Magnecore wires on this car. I tried a set since they worked very well on my other car, but the problem is the boots on the plugs are weak and difficult to remove. After a few remove/install sessions the boots ripped and the wires separated from the crimp terminals. I'm using NGK wires now and they're been great.
Also, make sure your plugs are gapped to .026" to .032" Anything bigger might misfire under boost.
I have a feeling your old plug wires were bad. Your symptoms point to spark blowout. I personally don't like Magnecore wires on this car. I tried a set since they worked very well on my other car, but the problem is the boots on the plugs are weak and difficult to remove. After a few remove/install sessions the boots ripped and the wires separated from the crimp terminals. I'm using NGK wires now and they're been great.
Also, make sure your plugs are gapped to .026" to .032" Anything bigger might misfire under boost.
#35
Burning Brakes
If it still cuts/ misfires, could you watch the wideband AFR to see how rich it gets right before the misfire? I'm interested in the richest AFR you see. The gauge might move quickly, so watch carefully.
#36
Drifting
It's probably just the spark plug wires that are bad because if you have a miss fire in the combustion chamber you'll have unburned fuel and oxygen that go into the exhaust showing your air fuel ratio meter that it's running lean because of the oxygen content in the exhaust, does that make sense. Just replace your wires you're gonna fix your problem most likely. you should probably replace your spark plugs, cap and rotor as well. I had to fix this post at a rest stop, driving and typing doesn't work well. And talking into the phone really doesn't work that well sometimes.
Last edited by Humboldtgrin; 01-07-2017 at 09:21 PM.
#37
Rennlist Member
It's probably just the spark plug wires that are bad because if you have a miss fire in the combustion chamber you'll have unburned fuel and oxygen that go into the exhaust show your air fuel ratio meter will tell you it's running lean because of the oxygen content in the exhaust does that make sense replace your wires you're gonna fix your problem most likely. you should probably replace your spark plugs and rotor as wellI hate my phone I'm trying to talk into it to explain and it is typing whatever it wants
#38
Cylinder 4
cylinder 2, very likely grounding with each other
Cylinder1
Ok so I cleaned my old plug wires yesterday and wrap them with splice tape. Made a coil wire out of some super heavy guage amplifier wire and the old crimp fittings boots from original. Well not original the boots were but had some coil wound replacement wire. Drove around and same symptoms.
Got a noid light and here are results
1 and 4 no light pulses
2 and 3 light pulses but inconsistent
I tore into my injector harness and here are the results
Cylinder 2 Was the only one obviously grounding out but the others were bad as well.
cylinder 2, very likely grounding with each other
Cylinder1
Agreed. Based on your description of the wires, I'd change them even if they weren't the cause of this issue. And, there's a reasonable chance they are the issue... Back in the old days, we'd open the hood in a dark (well ventilated) garage and look for arcing from the wires with the motor reving. Spark plug wires weren't as good in 60-70s, so it wasn't uncommon to see a little firework show. They have to be seriously bad to see arcing these days, but no harm taking a look.
Got a noid light and here are results
1 and 4 no light pulses
2 and 3 light pulses but inconsistent
I tore into my injector harness and here are the results
Cylinder 2 Was the only one obviously grounding out but the others were bad as well.
#39
After putting some electrical tape on the exposed sections i now get a steady 3 pulses from each cylinder per revolution. Pretty confident that's what is causing my car to stumble go lean. Time to get some replacement connectors and fix my harness up a little.
#40
Rennlist Member
Glad you found that. It's unfortunately all too common. I'd fix the spark plug wires too of course Some to your findings are hard to explain (3 pulses per rev?) but clearly you need to fix the harness regardless. The link below has info about the connectors. I wonder if the rpm-based change you were feeling was related to when the Vitesse system shifts from semi-batch to full batch --i.e., the effects of the bad harness gets worse in single batch mode -- though that's an academic question at this point I suppose...
https://rennlist.com/forums/944-turb...onnectors.html
https://rennlist.com/forums/944-turb...onnectors.html
#41
Glad you found that. It's unfortunately all too common. I'd fix the spark plug wires too of course Some to your findings are hard to explain (3 pulses per rev?) but clearly you need to fix the harness regardless. The link below has info about the connectors. I wonder if the rpm-based change you were feeling was related to when the Vitesse system shifts from semi-batch to full batch --i.e., the effects of the bad harness gets worse in single batch mode -- though that's an academic question at this point I suppose...
https://rennlist.com/forums/944-turb...onnectors.html
https://rennlist.com/forums/944-turb...onnectors.html
#42
Rennlist Member
Yeah, that's a design flaw. That sealant/glue/potting material inside the connectors just cuts the wire insulation over time. Probably worth doing the speed/ref connectors while you're at it, since they suffer from the same problem...
#44