Jody --

I was trying to get him to understand the VE --- get that close --- then leave that alone and fatten up the A/F... figuring that going from 14.3 to say 13.8 wouldn't "disrupt" the VE much.

I personally like to not make too many changes in too many tables - when trying to sort out a problem. Since he's happy with the tune - except just this one area he described... I was kind of thinking that if his VE is okay - then he could just change the one table (A/F) and see if that's the issue (a lean miss?).
Rather than messing up the VE table AND the A/F table too... if you get my reasoning?

I agree - that if - lets say he fattened the A/F to some point - and the miss went away... then he could go back and make sure his VE was accurate?

I might be wrong here - so I'm glad you chimed in.

I actually like working in my A/F tables and VE tables with the O2 in open loop... and when I'm seeing A/F's that match my desired A/F's with no correction - then I switch it back to closed loop... but I didn't want to complicate matter for him either.

you're right, assuming he has enough correction set up in the software he could simply adjust the a/f and let the competer adjust the ve to get there and see if it solves his issue.

Jody

I appreciate all the input from you guys, I ordered the fuel pressure sender kit from FAST today and will hook it up and head to the highway this weekend. This way I can data log whats happening with A/F ratio vs fuel pressure and look at all the paremeters, once I have this data I will let you guys know.

The closed loop correction limits at the area(52to 58kpa-2.0k-2.4k rpm, light cruise) that IM having problems is -25% and +22%

Thanks for all the help, more to come- Rich

Well I installed the fuel pressure sender and hooked it up to the ecu. Seems accurate, the regulator is vacuum referenced so my idle pressure is right around 40psi. If I pull the hose off the regulator it goes up to 44-45psi.

I had the opportunity to get it out on the highway for a solid 1 hour of highway time and data logged two 30 min sessions. Its at least 15 to 20 degrees(70F) warmer out than it was when the stumbles were occuring during last weeks criuse(52F). I let it idle in my driveway for 10 to 15 min hood closed to get it really warmed up before we hit the highway. Were cruising at 2200 rpm and at around 22 minutes into the first cruise we feel a very slight stumble and thats it the second 30min never felt a thing. So I look at the data around that time and I dont see anything major. The average fuel pressure is between 36 and 40 psi the actual A/F is around 14.5. I noticed the fuel pressure tracks the KPA graph very closely, I imagine this due to the vacuum reference. When I roll out of the throttle and rpm comes down getting off the highway the kpa goes down significantly(18kpa- 36psi) as does the fuel pressure. I really thought the stumbles would happen more frequently since it was warmer out but it didnt. Does the colder air make it much leaner? What do you guys think?

Thanks Rich

FWIW, I really enjoy reading this type of thread...I always learn something if not lots!!

Rich, you and the boys will figure it out!! :thumbsup:

Rich,

Okay -- Jody will correct me on this... but there is no reason at all to have the vacuum reference on the fuel regulator. That application is only for boost reference. But - if it was tuned with the vac applied - it should be okay. There's just no reason to have it. However, DO NOT plug the vacuum port of the regulator. It needs to be open to atmosphere.

I've been told that the IAT (Intake Air Temps) have very little to do with the actual references used in the ECU... I've been told this by at least 3 different tuners... but then - they could all be wrong too. Since I have 8 stack EFI - my IAT sensor is just kind of "hanging" between a couple of the stacks back at the rear of the engine. I've put it in a couple of places - and it doesn't seem to make any difference in anything.

Since your 'issue' seems to be so intermittent... I think I might be looking for an electrical draw. Maybe the voltage drops when something goes on? Causing a momentary blip in the ECU/sensor voltages.

I'd also be looking for a possible "hole" in the VE or A/F map - where your foot (TPS or MAP) just drops into this hole. If you have 3D visual on your system - look to see the junction at the perceived RPMs/Map signal (like 2200 rpm and 45kpa -- or wherever you think this fault happens) and see if there is a dip in the map or a "mountain" right around there...

Last thing I can come up with to check on - the voltage to the Fuel pump... I'm assuming you're running it off a relay.... and that it has a great ground system... and that it's not dropping voltage momentarily when your fans kick on - or the stereo kicks on - or the A/C compressor goes on etc.

I'm assuming also that you're using a ONE WIRE type alternator charging system (with no points style voltage regulator in the system) and that the alternator is capable of handling the total loads placed on it (i.e., the amp draw has been added up for all your systems and that the alternator is capable of supporting them all).

LAST... there has been some discussion about faulty MSD systems. Can't remember where this thread was - but there was an issue with them heating up and breaking down. One guy was icing his down for awhile until he sent it back for a factory look see... I just don't remember the issue or the outcome.

Rich,

I might add that I also think the cruise temps you mentioned (in your first post) could be part of the problem. Your first post mentions (proudly!) that your engine temps were around 165 degrees (if I remember right) and this could be causing the fuel in the intake to not stay atomized... and might help explain why - today - with the warmer air temps - your problem wasn't happening as much.

I raised my thermostat to 195 degree version. EVERYTHING works better now. The pistons (forged) seal better - I use less oil - and the motor just purrs... I also have a 427 small block. New fuel injected motors are running 200 degrees plus at operating temps. This is due in part to emissions (I think) - but I also think it helps with fuel injection.

Just a thought is all...

For what its worth, monitoring battery voltage in the data logs only one tenth of change from 13.5 13.6 occured. I do run a relay to the fuel pump and the grounds are real good. I tied the whole car together with 4 10guage multistrand wires lugged into a 4 guage lug terminals and mounted them everywhere. The fuel pump pulls power through isolated 8 guage wires directly from the battery back to the terminals on the relay in the back of the car.

The log did show an average of 175 deg of coolant temp. At that temperature if Im running a 180 tstat isn't it closed. The water temp had to be close to 10 degrees colder last week.

Rich,

Grounds and pump seem fine! Good job.

I'd love to hear what some of the more knowledgeable folks here think of the water temps. Yes - at 175 your thermostat would be closed. That is still a very COLD temp to be running - especially with forged pistons... they love some heat. And it just might explain the stumble... but I'm just guessing here now anyway.

what does the ignition system consist of ? What are you using to trigger the XFI crank signal ? cam signal ? where are the pick ups located ?


where is your coolant temp sensor for the efi located ?
do you have a temp guage also ? what does it read and where is it's sensor ?