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Ok, since you asked i'll correct that!
The O2 sensors measure O2 and not fuel. So it you have a misfire you will not burn the O2 during the misfire and it will show up at a lean AFR reading. If fact a misfire usually makes the ECU try to add fuel because it believes it lean when it really isn't.
Understood.
Originally Posted by Dan Martinic
Take the test DME offer! It would be very valuable to confirm that yours is indeed good. Your car ran fine then without any changes it started acting up, correct? And despite much time diagnosing including serviced by a pro, you're still far from the cause. Here's what was killing my car for a few weeks:
I hope you test fuel pressure and find the problem (PS the hard part is finding that rail end-fitting; some just clamp a hose on there briefly but you didn't hear it from me). But if it tests fine?
Trying another DME --even if your car is running fine-- can offer a lot info re: chip, general behaviour, etc. One time, after lots of work, my car wouldn't start. A super nice guy saw my posts and brought his DME over. No change. It was a major help. If I was nearby, I'd bring mine over. Moalaska is offering the next best thing
I appreciate the offers so much. The support on here is great. However, maybe my latest post sheds light on a pressure-related issue?
my best guess is that you have a wiring issue in the harness. Getting more and more common as our cars age. Kt sounds like you have been working on the engine (removing fuel rail / intake manifold etc.) - that means you have been bending the harness and that can crack the brittle insulation.
My usual solution is to recommend the possibility of stand alone system and completely replace the stock wiring. Yes, its a little extreme but from experience I can tell you that I have had customers spend more $ chasing bad wiring than the cost of a stand alone.
A truly hate old wiring!
This is one of my fears. Once I get the car running, I'm going to overhaul the harness.
Measured the fuel pressure at the rail and and it appeared within spec during the first 15 seconds, however, when it begins to misfire, the fuel pressure jumps to 100+ psi. At this point, I'd say its safe to assume that Rennwerke did not test the fuel pressure, as there is clear evidence of an issue.
However, the 15 second delay as well as the fact that the fuel pressure drops off almost immediately after turning off the car indicates that this may not be a FPR-related issue, but a check valve, damper, or clogged return.
I've attached a video so any input is much appreciated.
Thank you
that is very odd. The regulator is a purely mechanical device and should not do that - toss it out ASAP! I bet it will solve a lot of your issues.
that is very odd. The regulator is a purely mechanical device and should not do that - toss it out ASAP! I bet it will solve a lot of your issues.
Very odd indeed. I have seem some similar failures of Bosch FPRs on a few customer 911 3.2s, and I had a very intermittent one on my own 951, though none of these failures were as consistent as Tyler's seems to be, and they certainly didn't happen at idle!
In each of these cases, the failure would happen with the engine hot and after a big change in engine load/vacuum (big lift after a large throttle opening, for example). This would cause the failing FPR to somehow completely block off the fuel return line, and fuel pressure would go sky-high. One of the 911 3.2s would completely stall because the fuel injectors could not open against almost 100 PSI of fuel pressure, but the engine would restart right away. My own 951's FPR failure was especially frustrating because at first it would only occur towards the end of a track session on a hot day, then would be totally OK on the street. Black smoke would emit from the tailpipe and the engine would bog down, but rapidly pumping the gas pedal would unstick the FPR and the engine would run normally once more.
Tyler, I still think you should replace the FPR in any case, but it might be wise to disconnect both ends of the fuel return line and blow it out. It would be odd, but there could be something stuck in there that gets lodged in one spot after ~15 seconds of running that causes total blockage of the fuel return. Maybe replace the rubber sections of the return hose as well, as there could be an inadvertent "check valve" happening inside one of those. I've seen this happen in old brake hydraulic hoses, but not yet inside a fuel hose . . . .
that is very odd. The regulator is a purely mechanical device and should not do that - toss it out ASAP! I bet it will solve a lot of your issues.
Ordered a 3Bar Bosch unit today. Hope to have it in this week and see. I too don't understand the timing consistency.
Originally Posted by Droops83
Very odd indeed. I have seem some similar failures of Bosch FPRs on a few customer 911 3.2s, and I had a very intermittent one on my own 951, though none of these failures were as consistent as Tyler's seems to be, and they certainly didn't happen at idle!
In each of these cases, the failure would happen with the engine hot and after a big change in engine load/vacuum (big lift after a large throttle opening, for example). This would cause the failing FPR to somehow completely block off the fuel return line, and fuel pressure would go sky-high. One of the 911 3.2s would completely stall because the fuel injectors could not open against almost 100 PSI of fuel pressure, but the engine would restart right away. My own 951's FPR failure was especially frustrating because at first it would only occur towards the end of a track session on a hot day, then would be totally OK on the street. Black smoke would emit from the tailpipe and the engine would bog down, but rapidly pumping the gas pedal would unstick the FPR and the engine would run normally once more.
Tyler, I still think you should replace the FPR in any case, but it might be wise to disconnect both ends of the fuel return line and blow it out. It would be odd, but there could be something stuck in there that gets lodged in one spot after ~15 seconds of running that causes total blockage of the fuel return. Maybe replace the rubber sections of the return hose as well, as there could be an inadvertent "check valve" happening inside one of those. I've seen this happen in old brake hydraulic hoses, but not yet inside a fuel hose . . . .
Interesting insight. I'm trying to understand why it is happening this way, and also, what about these running circumstances causes the KLR to pull back spark on boost. Could it have to do with injectors drawing too much power? According to my wide band, I'm not going even close to lean under boost.
I most definitely plan on replacing the rubber fuel hoses because their age is unknown to me.
I'm also curious what caused the fuel pressure to leak down so quick.
This is one of my fears. Once I get the car running, I'm going to overhaul the harness.
Overhauling the harness isn't particularly hard, just requires soldering knowledge, patience. All the connectors can be purchased, except for the o2 sensor one I think, and oil level sensor. There's one for the turbo water pump I think that can be substituted for a female bullet. I pulled my entire harness, and redid all the wires from behind the firewall, with all new connectors, soldered, heat shrinked, and wrapped in fiberglass foil sheathing, which actually saved my butt when power steering fluid shot onto my exhaust manifold and I had flames coming out my hood louvers. I do I remember correctly, eagleday was the supplier I used for most of the odd connectors, like the tps. And upgrade your injector connectors with press release ones. My injector wires were all shorted out right behind the connector, it's a common problem on almost all of the connectors on the 30 year old harness. That's why there is a thread at the top of the list about a new harness vendor.
You could also do a fuel flow test if you get bored. I think there is a thread somewhere about how much fuel you should have in a bucket after like 30 seconds or something. I can't remember how the first rail system is, mines custom, but if you have a loose piece of rubber in your system, from say a failed fuel damper, you could have weird stuff happening, if it blocks your return you would definitely have a rich condition!
Glad you found something amiss with the fuel pressure testing. A little curious why the mechanic didn't... but if I recall corrcectly, the car ran fine for a couple weeks after picking it up? I guess this issue could have appeared after servicing
Everyone's always complaining about the wires; guess I'm lucky mine are holding up so far. Maybe it's the wd40 I keep spraying all over the engine... you know, to get that shine lol! I do have a new reference sensor harness waiting on the shelf..
Installed the new FPR and everything fuel wise is great. The car now idles in the 14.6-15 AFR range and hits about 11.7 under boost.
After putting about 180 miles on my car happy to have it back, it developed a slight misfire under low RPM load. Took it out again yesterday and it was misfiring so hard that I could barely get it home. It then began stalking every time the RPM returned to idle.
On getting it home, I know three things required testing - fuel, air, spark. My plugs, wires, distributor, rotor and coil were all replaced about 200 miles ago.
Upon pulling the plugs, I noticed a bit of oil in the threads, but they were not fouled and black as before. I do seem to have failing turbo seals, though a rebuilt K26/6 was installed maybe 500 miles ago. I cleaned the contacts assuming maybe oil was shorting the spark or a similar scenario. This made no difference. I then tested the coil for voltage and noticed that it only indicates 1.1v when it should indicate 12v. The battery charge indicated 11.7v, however that was after trying to crank the car for a bit as it now won’t start at all. Fuel pressure at the rail is fine and the pump is operating normal.
Assuming the low coil voltage is the culprit (that’s my best guess at least,) is this an issue with the resistor in the DME that grounds out the coil? Is there anything else I should check?
I would love to put some miles on this thing as the weather is getting nicer.
Borrow that DME. With a known good DME, you will either get your answer or confidently continue checking for bad wires & connections.
I that's not an option, perform some continuity tests on the coil wires, tracing them back. If those seem fine, open the DME and with your phone camera zoom, look for the hairline cracks as shown in post #31
Installed the new FPR and everything fuel wise is great. The car now idles in the 14.6-15 AFR range and hits about 11.7 under boost.
After putting about 180 miles on my car happy to have it back, it developed a slight misfire under low RPM load. Took it out again yesterday and it was misfiring so hard that I could barely get it home. It then began stalking every time the RPM returned to idle.
On getting it home, I know three things required testing - fuel, air, spark. My plugs, wires, distributor, rotor and coil were all replaced about 200 miles ago.
Upon pulling the plugs, I noticed a bit of oil in the threads, but they were not fouled and black as before. I do seem to have failing turbo seals, though a rebuilt K26/6 was installed maybe 500 miles ago. I cleaned the contacts assuming maybe oil was shorting the spark or a similar scenario. This made no difference. I then tested the coil for voltage and noticed that it only indicates 1.1v when it should indicate 12v. The battery charge indicated 11.7v, however that was after trying to crank the car for a bit as it now won’t start at all. Fuel pressure at the rail is fine and the pump is operating normal.
Assuming the low coil voltage is the culprit (that’s my best guess at least,) is this an issue with the resistor in the DME that grounds out the coil? Is there anything else I should check?
I would love to put some miles on this thing as the weather is getting nicer.
Thank you all for the insight.
Which coil terminal is measuring 1.1V? And is this with the key on/engine off or while cranking? This is one place where a test light is your friend, as a digital voltmeter will only display the average voltage of a circuit and not register any switching signals. You should have steady battery voltage at the coil positive terminal while cranking, and at the negative terminal, the test light should rapidly flash on and off while cranking if the DME ignition driver transistor is good. If it is not good, then it will show solid voltage or nothing at all.
If the ignition driver circuit seems to be switching the coil on and off, then move onto the secondary ignition circuit and check for spark at each point (coil, distributor, plugs).
Oh yeah.. the 12v led! I keep forgetting how useful that thing is! Helped me a ton a while back
Here's an example of what it looks like testing the coil with a little 12v LED you can get for peanuts at an electronics supply (it's the green thing flashing on the left)
I am seeing 1.1v of power when testing the power and ground points of the coil when the key is turned.
That's not right, you are either probing the wrong wire for the coil, or something is messed up. Try jumpering the DME relay points for the ignition side.
That's not right, you are either probing the wrong wire for the coil, or someone is messed up. Try jumpering the DME relay points for the ignition side.
I had a weird issue at some point in time where I didn't have enough power to the 87b terminal, I think that's what it was, it was the terminal for the ignition in the fuse block. I completely disassemble the fuse block and cleaned all the buss bars, then I found a bad wire on one of the connectors underneath . Jfyi.
04-26-2020, 05:21 PM
