Working on a 94 Formula M6.

The car starts fine from a cold start and runs lie a scalded dog, as it warms up you can feel some power loss through the rpm band. After about 30 minutes of driving you run out of power bad passing 3500 to the point of shutting off at about 4500 under heavy loads. If you let off it wakes right back up but repeats the same process. If you keep driving through the day ( errands and such) after a few hours the loss gets worse lower in the RPM to the point of shutting off at idle. When this happens park it key out for 30 seconds and it fires back up and pulls hard for about a minute repeating the process.

I logged the event last week and seem to have since wiped parts of it ( I dont know how) from what I saw I appeared the car was going rich when this happened so I disabled the BLM with no change. No knock retardation showed. I have replaced the ICM and Coil on warranty. The Opti was replaced last year with the water pump. Today during the issue I shut down teh car and ran on just MAP and just MAF both without improvement. I have brand new O2 sensors from 2 months ago and all temp sensors are reading within normal limits. I just tested fuel pressure pump on engine off 43psi, car idle vac off 43psi from idle to about 3k without load, and idle with vac is about 38psi. The pressure dose fall off to zero in the time to walk from the drivers door to the passenger fender.

I am at a bit of a loss now

 

Disconnect your 02s and drive it like that. See if the power stays.

 

wouldn't disabling blm give you the same result?

Ill still give it a try, just wondering

 

That depends on what is causing the issue. All of your BLM cells are adding a lot of fuel, maxed out in some cases. But none of them ever came down close to target BLM of 128, in any cell.

Did you have it tuned for your mods?

The symptoms you are describing is timed with closed loop enabling. Closed loop needs to have 2 things before it's engaged, a specific coolant temp (90 to 140 degrees f) and a minimum amount of time (between 50 and 215 seconds depending on coolant temperature). First start up, especially when it's less than 60°f out, it'll take a bit to warm up. Longer than the minimum time required (for O2's to properly heat up). After initial start up and coolant temp is reached, you'll reach closed loop sooner (2nd start of the day) as the coolant temps are already reached.

You describe the symptoms to start kicking in at around the time closed loop kicks in. Disconnecting the O2's forces open loop. This forces the engine to fuel based solely on the MAF (or VE tables depending on the tune in your vehicle). If you disconnect the O2's and the problem goes away, you'll need to look into possible exhaust leaks or vacuum leaks (if running the MAF). Or bad 02's.

If you disconnect the MAF and leave the O2's connected it'll force SD mode (using the VE tables), but still use the O2's for feed back and BLM trim adjustments. With your mods, if your VE tables have not been adjusted to your build I wouldn't recommend doing this. Because the VE tables are going to be wrong and it'll likely run like poo. But, may be worth a shot to do if disconnecting the O2's in MAF mode doesn't fix the issue. But, you need to take into account that if the VE tables have not been tuned to your engine the result of this test is not going to be conclusive to the root of your problem. You'll know quickly if your VE tables are tuned to your engine or not by disconnecting the MAF and driving the car before it enters closed loop mode (so in less than 50 seconds if the engine is already warmed up), it'll run like utter crap if they are not tuned.

Also, any other mods than what's in your sig? Headers? CAI? etc.?

Hope this helps.

 

The only thing not listed was a refresh, stock bore and stroke within tolerances just honed with new rings bearings and gaskets due to a spun bearing on the #8 connecting rod. The porting was not a hardcore port just taking the casting flaws out.

I was running the engine without working o2 sensors for about a month or 2 ( I didn't know they failed because the SES is always on from the egr delete) The only complaint when running without o2 sensors was poor economy and running very rich.

I replaced the o2 sensors around Dec 1 2016 and the issue surfaced the last week of January.

When I started to notice the issue I did attempt running the car with a fuel pressure of 48psi and seemed to make the car run worse and has since been backed down to 43psi.

because these are the original manifolds and have been on and off a few times what is the likely hood of a crack?

 

So fixing the 02s created these symptoms. Do you have a tune? If not, I'd say you need one.

 

I disconnected the o2 sensors and there is no change. Also the onset was almost 2 months after the o2 sensors where installed

 

Did you try disconnecting the MAF? O2s connected and see if it improves. It could take a little while, unless you wipe the BLM memory with Scan9495 or $EE Hack.

 

I just noticed you said the fuel pressure drops to zero quickly. I'd pull the fuel rails and see if you have any leaking injectors when you prime the fuel pump (key on engine off). A leaking injector can cause your symptoms, but the BLMs would usually run below 128 if that was the case. Instead your engine is asking for more fuel.

Disconnecting the MAF should help you know if it's either a bad MAF (or tune) or a vacuum leak. That's assuming the VE tables are close enough to what your engine wants with the mods you have. The 02's will help SD mode get the fueling closer if the VE tables are a bit off. Make sure you datalog this though, so you can see what, if any, differences it makes. It'll also tell you if the VE tables need to be tuned and by how much and where.

 

Thanks for the help. I am going to pull the fuel rail in a few to see about the potential leak. I'll try datalogging tomorrow on my way to work (45 minute drive) on SD only. I did try driving home on SD without the o2 sensors and it drove exactly the same way. One thing I do remember from learning to use megasquirt was that if a narrow band is rich enough it may show lean, I had this working on the v6 firebird.

 

If forcing open loop and forcing SD does nothing, then you'll want to look into a heat induced failure. The thing with the SD mode is, if it fixed the issue you'd know it was the MAF, but if it didn't you really don't know anything because if the VE tables are not tuned to the cam/build it'd run like poo.

Usually, heat induced failures are on electrical components and lead to engine shut down not loss of power.

Turning the engine off then back on forces open loop for a little while, and only off for 30 seconds I wouldn't imagine it would give enough time for anything to cool down significantly enough to change operating behavior.

If you had a crack in an exhaust manifold (or a leak on or around it), you'd know it. You'd hear it. Like a constant popping sound. It could also be mistaken for lifter tick or even rod knock depending on how bad the leak is. An exhaust leak would cause a rich condition, like you have.

Have you tried resetting the BLMs?

 

So I got some data logging done. MAF unplugged and first data log is with blm cleared disabled and in open loop only this is listed as all off. The second I allowed closed loop to allow short term fuel trims only. Both where recorded on my trip to town about 20 mins each way.

on teh all off trip the first pull was 3rd gear into 4th without any issues. The second was same 3rd to 4th gear pull with power loss at 5k.

The return trip of BLM off both pulls where 3rd into 4th with power loss at 3500rpm. The last pull added what felt like a jerking studder. There was a decrease in power across the rpm range but it did not seem as pronounced as usual.

I did have an exhaust leak last year when I did not seat the passenger side down pipe to the manifold. I tightened it up as soon as I found it summer last year.

 

Why haven't you gotten a wide band on the car and watched the air fuel during this period when it loses all power. You're logging so you should be able to see if timing is dropping over time and a wideband will tell you what the air fuel is doing.

 

because I don't have $200 to spend on a sensor or the tools to add a bung at the front of the cat and this is the first controlled data logs I have been able to take.

 

Looks like you're getting knock retard. It's trying to add fuel, according to your O2's you're running very lean. That lean leads to knock, which leads to knock retard, which is what you're feeling.

You can hook everything back up now. What needs to be looked at now is why you're getting knock. Or why you're engine is seeing it (possibly false knock). In the "BLM Off" log, at only 26% TPS and 1819 RPM it shows a burst of knock and 8° of knock retard, you'll definitely feel a loss of power with that much timing pulled. There should be no reason for you to have knock in this range under those conditions on a healthy engine.

Maybe bad gas, but that would only last for that tank or so.

You're running lean, which is why it's adding fuel. You need to find out why you're running lean....

Unless you got a bad batch of gas (maybe ran the tank too low too??) and got the injectors dirty. If that's the case, the injectors won't flow correctly and you'll be running lean even though the engine is commanding more fuel.

It's not holding fuel pressure like it should, but it maintains it while running. I'd still check for leaking injectors, but it's most likely the FPR or check ball on the fuel pump causing the rapid drop in fuel pressure after priming.

I'd check the injectors to see if any are leaking (I'd be surprised if they are), then I'd remove them and have them cleaned. I'd also replace the fuel filter and flush the fuel lines too.

You could also replace the knock sensor too. But, with the lean condition plus the knock retard I'd lean towards clogged fuel injectors.

 

I wish it was bag gas but being this is my daily driver bad gas would have only lasted a few days. I pulled the rail earlier today and tested with no leaks. I will be doing an oil change this week so I'll grab a fuel filter to go with the rest. I have a sneaking suspicion I can trace the pressure drop to the hose from the pump to the sending unit as I have had to replace the hose before with a fuel leak. The pump was replaced when I bought the car ( along with a ton of other things to get it running) and the original plastic fuel line they sent split.

 

I looked over my logs again and noticed a trend. The first run had a WOT injector pulse of about 15.5ms on both pulls only running lean on the second. The second log shows a WOT pulse of about 26ms( nearing the max 80% duty cycle) and running lean on both. From this it looks to me like I must be loosing pressure as time elapses. Would it be safe to say I may be looking at a failing pump by there observations? Checking for a leak and new filters will definitely come first but it was a thought.

 

A failing pump could be likely with your symptoms. I was leaning towards clogged fuel injectors.

Hook up a fuel pressure gauge while it's acting up, that'll tell you what you need to know about the pump. See if you can get the pressure gauge up high enough for you to tape it to the windsheild while you're driving.

 

you have front o2s don't you? Put it in open loop and stick the wideband in the place of each of the front o2s so you can see what each bank I'd doing. Trying to use fuel trims and stock o2s is like using a compass instead of a gps.

 

Yes. But it's possible. Although it's a lot faster with the wide bands.