One last shot... Breaking up!

[turboj91]

Re: One last shot... Breaking up!

Your issues at a specifc rpm are not unheard of but I usually hear of problems at a higher rpm rather than a lower rpm. I can see your frustration. What are you able to monitor at the problem rpm spots? I would be curious to see what the timing does, duty cycles, fuel pressure ect. Obviously something is changing for the worse but then clears up. I would assume the fuel pump is not the prob since it can produce at a higher demand level and I would assume the plugs, wires, cap, rotor, dist module ect are all good (I think you have replaced all these anyway). Have you checked vacuum at the problem rpm's. Seems the prob may be at high vac readings. Above 3K and on the boost you are no longer under high vac. Wonder if something is leaking at high vac and causing a lean misfire? BTW, have you checked the pcv valves to make sure they are clean. It is a long story but I ran into a pcv problem once which reared its ugly head once the vehicle came up to operating temp.

 

[BoostedSUV]

Re: One last shot... Breaking up!

Interesting thought... I've checked the PCV valve placing my finger over it while the truck was running and I had vaccum and when my thumb went over it the check valve closed. Beyond that I don't know what really else to test with the PCV sytem. I can monitor fuel pressure and vac from inside the truck and neither do anything irratic at any RPM range and nothing specific that I can see happens at my problem spots. It is very strange to me how specific the rpm is when I have the issue. Once the truck warms up it hesitates at 1500 and 1900 and at 2500 it really sputters and drops lean. I've monitored each sensor with datamaster hooked up and I've had a few people go over the files, but nothing jumps out indicating a problem. The truck just seems to get a really bad lean miss at 2500 and O2 and WB show it clearly. Once it gets passed 2500 WB and O2 read normal and the truck runs smooth. The only thing I can point at is the fact that the warmer the engine temps get the worse my lean miss gets. Also the more fuel pressure I add the worse it gets. If I drop FP it gets better but I have to turn the base FP down lower than I'm comfortable with. Very frustrating.... We're all missing something.

 

[WyoSyclone]

Re: One last shot... Breaking up!

I've read all the posts again... do you have another AFPR you could put in? You disconnected the o2 and it didn't change anything. You say you have some strange vacuum readings. You have shown that changing fuel pressure alters the problem. Can you disconnect the line from the afpr and go for a gentle, light throttle drive through the 1500 and 1900 rpm range and see if the prob is still there? I'm wondering if when the diaphragm in the AFPR gets stretched that it may be opening up a void of some type that is altering your mix?? .....just a long shot

 

[BoostedSUV]

Re: One last shot... Breaking up!

Rob that's not a bad thought... I've thought about the AFPR but figured what the hell can really go wrong with one? It holds pressure and moves with vac but anything is possible. I do not have a spare but I guess what I can try is removing the vac line and plugging it, drop the base pressure to about 38 (where it idles with line connected) and see what I get. Easy enough to try... Am I thinking along the right track?

 

[Quickstop [UK]]

Re: One last shot... Breaking up!

if it is broken then you'll be testing with a broken one so you may not know...

 

[WyoSyclone]

Re: One last shot... Breaking up!

if it is broken then you'll be testing with a broken one so you may not know...

With the line disconnected the diaphragm won't be moving, so it should just provide a steady, non-rising FP... if you don't get any breakup with the line disco'd it will at least point towards a mechanical fuel delivery problem.

 

[turboj91]

Re: One last shot... Breaking up!

I just read the entire file again (fun Friday night). Where does your sensor get the fuel pressure reading? I know the pressure does not change to indicate pump failure but could something effect fuel flow after the sensor? If not, since the engine goes lean, it looses fuel somewhere/somehow at the aforementioned rpm's. Can you/have you read duty cycles at the troubled rpm's. Injector duration and pressure determines the amount of fuel thru the injector unless the injector is dirty/clogged but it seems illogical that the injector could be clogged and then clean itself out once you reach above 2500 rpms and then go back to the problem again once rpms are back down to 2500. Maybe back to basics like some have suggested. I believe you have had the O2 disconnected at operating temp and it did not throw a code. You worked on the O2 "circut" when you changed gauges. O2 controls fueling. Wondering if some type of improper signal or interrupted signal disrupts injector operation. Wondering if the O2 reads lean at the troubled rpms, what if anything does it do to richen the mixture. I have always said, new only means nobody used it before you. Wouldn't it be a beotch if both O2 sensors were bad in the same way. Something that does not cost any $$ is to re-trace everywhere your hands were touching things and bumping into things when you originally changed gauges. Was previously thinking vacuum leak but then why doesn't the O2 compensate for it or is it too much of a leak to compensate for. Duty cycles would tell you that. Things move and expand as the engine heats and vac. leaks can appear but one would think that the leak doesn't care if it is in open loop or closed loop and why does it not have the same problem in open loop but at operating temp. Typing in circles. Need to stop for now. Still interested in progress though.

 

[BoostedSUV]

Re: One last shot... Breaking up!

I just read the entire file again (fun Friday night). Where does your sensor get the fuel pressure reading? I know the pressure does not change to indicate pump failure but could something effect fuel flow after the sensor? If not, since the engine goes lean, it looses fuel somewhere/somehow at the aforementioned rpm's. Can you/have you read duty cycles at the troubled rpm's. Injector duration and pressure determines the amount of fuel thru the injector unless the injector is dirty/clogged but it seems illogical that the injector could be clogged and then clean itself out once you reach above 2500 rpms and then go back to the problem again once rpms are back down to 2500. Maybe back to basics like some have suggested. I believe you have had the O2 disconnected at operating temp and it did not throw a code. You worked on the O2 "circut" when you changed gauges. O2 controls fueling. Wondering if some type of improper signal or interrupted signal disrupts injector operation. Wondering if the O2 reads lean at the troubled rpms, what if anything does it do to richen the mixture. I have always said, new only means nobody used it before you. Wouldn't it be a beotch if both O2 sensors were bad in the same way. Something that does not cost any $$ is to re-trace everywhere your hands were touching things and bumping into things when you originally changed gauges. Was previously thinking vacuum leak but then why doesn't the O2 compensate for it or is it too much of a leak to compensate for. Duty cycles would tell you that. Things move and expand as the engine heats and vac. leaks can appear but one would think that the leak doesn't care if it is in open loop or closed loop and why does it not have the same problem in open loop but at operating temp. Typing in circles. Need to stop for now. Still interested in progress though.

I appreciate you taking the time to read through everything and hop on board to help my issue. The more minds behind this the better chance I have of solving it.

The FP sender is on the fuel rail at the test port with an adapter fitting, I can't really imagine I'm loosing pressure else where in the system and it's not showing up on the gauge, but who the hell knows? I've seen stranger things...

As far the Injector cycle duty.. I don't remember the exact numbers but when I had datamaster hooked up the O2 readings showed lean and the injector cycle duty did increase to compensate the lean symptoms.

another thing is the Wideband which is an idependant unit, on a seperate sensor further down the exhaust stream and it shows lean as well right when the truck starts having the issue. Due to that I don't believe it's a false O2 signal triggering the injectors. I am going to try to get a better datalog file this week and post it be looked at.

I'm also starting to think it's an RPM/engine temp related issue and not "closed loop" since the O2 being unplugged does not change anything. Also when i'm into boost it is in "open loop" but I'm passed 2500 RPM so the problem wouldn't show up anyway... very confusing.

 

[turboj91]

Re: One last shot... Breaking up!

I talked to a guy this morning about your truck. He mentioned water temp sensor. He had a story about a bad unit that is some way, shape or form can be related to your issue. I would think that if the temp sensor was reading /sending cold signals when the truck was at full operating temp it makes the system want to richen the mixture. Maybe the sensor is reporting a running temp of 300+ degrees to lean it out as much as it does (being sarcastic as I don't think that is the case and don't even think the sensor has that capability). I think that is the only part you have not replaced. But to think about the temp sensor some more, if it in fact was defective, why would it clear itself up above 2500 rpm. No logic there. Your wideband is on its own. It reads lean and the engine breaks up so most likely the lean reading is correct. Now if the O2 reads the same lean condition it should react accordingly. Can you tell exactly what the O2 and the injectors are doing to compensate for the lean condition? at the exact moment/rpms that the problem occurs. They should be reading the system the same and the O2, if working properly, sends its signal and it is combined with all the other sensor info and a mixture is determined. Ultimately, I think a sensor is sending wrong info or the system is decifering the info incorrectly but you have changed about every sensor and the ECM. I think you have covered all the mechanical possibilities as far as fuel delivery up to the injectors. Need to determine exactly what happens from that point/at that point. Maybe you can pinpoint what sensor is wrong from there. I think the O2 has the most input to the ultimate mixture and believe it or not, it may still be your problem.

Ironically, I am going to a guy's house this afternoon to set up a 72 Chevelle with all its orig equip. It has two vac hoses. One for the vac advance and one for the power brakes (PCV deleted). Way at the other end of the spectrum from these trucks.

BTW, how much does it peak your curiosity that when you unplug the O2, it does not throw a code?

 

[BoostedSUV]

Re: One last shot... Breaking up!

That's temp sensor has been mentioned before in this thread, and in another thread of mine where I get a hard starting condition with my truck once it's warm. Could be unrelated but everyonce in a while when my truck get hot it does not want to start. It just cranks and tries to far but doesn't. I determined with datamaster running that when the truck is cranking the ECU sees 6500 rpm (never figured out why) and injector cyle duty jumps to 96 percent and it floods the motor so it won't start. I have to hold the throtte wide open in order to out it into "flood mode" and the truck will start and idle rough until it clears up the excess fuel in the cylinders.

Back to this issue... That coolant sensor reading shows on DM and it always reads normal. Its outside temp when I first start the truck, and it reads around 175-190 operating temp depending on the day etc. No weird reading there or on the intake temp sensor. That sensor was changed when I put the motor in the truck because I broke the connector off of it with the engine hoist chain. Regardless the reading looks normal. I guess its possible that O2 could be bad but its hard to say when both the O2 and WB show lean at the same point. I have the old sensor I can throw in to see if it still does it at 2500. The odd part is the specific RPM it does it, and the fact that it does it every time once I'm in "closed loop" or at engine operating temps. Also the fact that the warmer it gets... Say 190 degrees plus the worse it gets, the more fuel I add the worse it gets... I'm stumped.

 

[BoostedSUV]

Re: One last shot... Breaking up!

BTW, how much does it peak your curiosity that when you unplug the O2, it does not throw a code?

That does make me wonder...I don't know how long it should take to kick up the code but I had truck running for at least 20 mins and it did not throw an O2 code and the sensor was unplugged the entire time. I did not have the laptop connected at the time to see if my O2 "readings" went away and it kicked it into "open loop". That did make me curious and I posted about it and I didn't get any reply about the code not kicking up.

 

[BoostedSUV]

Re: One last shot... Breaking up!

If I unplug the MAP, IAC, EST bypass, or TPS I get an instant Check Engine light. Not with O2 sensor though... Just thought I would mention that. It's not like the bulb is burned out or anything.

 

[turboj91]

Re: One last shot... Breaking up!

I know some Pontiac guys that would want their engines to turn over at 6500 when warm. What kind of starter do you have? (lol - j/k). Might have some relation to your ultimate problem though. Improper tach signal ="s improper ecu calibration of mixture and it is odd that your problem is rpm specific. Gonna quote a saying from Bubba the Love Sponge show. "So what cha gonna do about it"? See if you can follow changes when the O2 reads lean. How much does the system try to compensate. Is the O2 working within its parameters. I know others have read your DM files and the people reading know what they are looking at. We need to read more data to get beyond the obvious and what is available to us at this time. I'd love to know the working parameters of an O2 ie; when it reads lean at 17:1, what is it supposed to signal back to make the system richen up and if yours works within the exact design parameters. If it is fine then there is other corrupted data in the system. Now to just find where that corrupted data comes from. Since I think most politicians are corrupt, you don't have one hiding in your truck do you? Off to my time machine for now. Back to 1972.

 

[general's servant]

Re: One last shot... Breaking up!

I know you have look at every possible thing but could it be you have some water in the gas tank?

 

[BoostedSUV]

Re: One last shot... Breaking up!

I know you have look at every possible thing but could it be you have some water in the gas tank?

I did just fill it prior to the issues but I'm just about empty. I'm going to fill it up later in the week and see if that helps

 

[BoostedSUV]

Re: One last shot... Breaking up!

I tried running the truck with the vac line disconnected to the AFPR and plugged and that did not help.

I made a few datalogs tonight and sent them to Nolan to look at. I did one at 50psi base pressure, 40 psi, and 30psi... the lower I go the less the truck breaks up! I put a manual gauge in place of my electric and verified the FP reads correctly.

 

[nallj92]

Re: One last shot... Breaking up!

whats your fuel map look like around the time of the lean conditions? any large differences. I think im chasing the same issue as you now, Just havent had time to really mess with figuring it out yet.

 

[BoostedSUV]

Re: One last shot... Breaking up!

whats your fuel map look like around the time of the lean conditions? any large differences. I think im chasing the same issue as you now, Just havent had time to really mess with figuring it out yet.

I can send you the DM files... when the truck goes lean and misses the injector cycle duty increases, and the truck tries adding more fuel. Nothing significant changes on the FP gauge but something crazy is going on either with fuelling or ign missfire "tricking" O2 into a lean condition....

 

[BoostedSUV]

Re: One last shot... Breaking up!

ok I did a few DM files and went over them with Nolan and he sees what i see... The more fuel I add (base pressure turned up) the leaner the truck shows and the more fuel the PCM tries to add, the less fuel I add (dropping the base FP) the richer the truck shows and the PCM tries to pull fuel... does that make any sense??? Completely opposite of what's supposed to happen! I tried it with FP base at 50, 40, and 30. The lower I go the better the truck runs but that's not the fix. I've got something really wacky going on!

 

[nallj92]

Re: One last shot... Breaking up!

did you try injector swap, i have brend new 60's but seeing the same issue, brand new engine, etc. under cruise it will run around 15afr and slwoly creep up to 18 afr's then miss. Im going to take a look at my csv log from tunerpro and see what different rpms and paramters it goes lean at. my inj duty cycle was high also from what I remember. It seems to me its a intermittant problem for me, it comes and goes randomly. im running and brand new wideband also.....