Bones232

Not sure if this is the best place to post this. Part of my problem is I don't know if this is an engine management problem or mechanical. I guess I'll start here.

So, I’ve had this engine for about 10 years and have been chasing my tail for just as long. I could just never get it to run right. My current setup is in my sig.

WOT is pretty straight forward and runs ok. I can generally get a good idle. What I don’t have a handle on is the cruise. Since day one BLMs have been useless to me. My fueling requirements seem to change constantly and drastically. Without some kind of consistency how am I supposed to get a good tune, right?

Over the years I’ve changed the following;
Fuel pump
Fuel pump wiring
Supply/return Fuel lines (like 3 times)
vafpr
Injectors (stock & 68pph)
3 different ecms (8746, ebl & 7427)
SD & Maf configurations
2 different cams (one with 114LSA & one with 110LSA)
Plugs (couple different sets)
Wires (couple different sets)
Cap & rotor
Distributor
ICM
Coil
MSD and No MSD

Recently after messing around with a MAF setup, I’ve noticed that the issue appears to be rpm related lean spots. The first spot develops below 875. I don’t know where the bottom is as the engine doesn’t usually see a lower rpm. The next starts about 1225 and increases sharply to a peak at about 1350 and then trails off by 1450. The third lean spot develops at about 2200 and lasts until about 2800. 3000 and up seem ok. The lean spots are worse at lower MAP values (<60). However, they are still present at heavier loads also.

The lean spots also seem to increase in severity with engine bay temp. The warmer the engine bay gets, the worse the lean conditions get. I’ve had to nearly double the BPW in these areas to help compensate. It just never seems to be enough though.

One thing I’ve noted about the lean conditions is their relationship to each other. If you look at 1350 rpm, which is the peak of the 1225 to 1450 lean condition, multiples of 2 fall within the other lean areas. For example;

1350/2=675
1350x2=2700
2700x2=5400 (I shift at around 5k so would see this normally)

I suspect there is some kind of resonance frequency at work here. Of what, I don’t know.

It’s extremely frustrating going to such lengths with virtually no effect on the problem at hand. With that said, I’m tapped out. I have no idea where to go from here. Abandon TBI? Tear down the motor????

Bones232

I threw my o-scope on the driver side injector today. Viewed at the ECM, the wave form looks clean. Viewed at the injector, i can see some anomalies. The one that sticks out the most is at arrow #4 in the attached picture. It kind of looks like the injector is trying to fire. Arrow #3 shows the height of the peak for that anomaly.

Anybody see this as something to be concerned about?

91 1LE

iTrader: (1)

I wouldn't be worried about the oscope reading. I don't think it's enough to open the injector. Are you sure its a lean condition and not a misfire caused by something in the ignition? Looks the same to a wideband...

Bones232

It sure feels like a lean condition. It pops and stutters like mad. It doesn't smell rich either.

I recently went the route of misfire. Changed distributor with a reman, icm, coil, wires, bypassed msd, new plugs, new cap & rotor. I don't know what else to replace.

The cap was ugly though. Several posts were corroded pretty good. The car definitely ran better after replacement, However the lean spots persist.

Ronny

iTrader: (1)

I too see VE-Learn adding a lot of fuel at 2000 rpms at 45 map. My low speed VE has a pronounced peak there. I think that is where I cruise often in 4th of 5 at 55 mph and 5th of 5 at 70 mph. It is not reversion as I have a 114 LSA. What we are seeing may be fuel velocity related. Low engine speeds possibly the O2 sensor reads lower volts and requests more fuel?

You bring up a good point as far as the BPC/BPW goes I may need to increase it at 40-50 MAP making it a small injector increasing fuel there?????

I dont think lean is a good word as the engine should be at stoich regardless with a higher than expected VE value and or a higher BLM.

Bones232

Does yours vary with underhood temps? I say underhood temps because i've datalogged cts, iat & mat and have found no definite correlation to the magnitude of the lean spikes. All i really know is the condition gets worse the hotter the car gets.

I've gone as far as to create cts/mat/map correction terms in attempt to isolate the cause of the spike.

If it was always 90degF outside I could probably get it to run good. Problem is the temp obviously changes and that tune used for 90degF will be unbelievably rich in 60degF weather. Common sense would tell you an engine needs less fuel the warmer it gets.

Ronny

iTrader: (1)

I dont understand the question? I believe I am neither lean nor rich. stoich.

My VE table shows higher than expected #'s as in a peak as a result of VE Learn.

Season to season yes tend to show higher/lower BLM. Day to day consistent unless cold/warm front.

I have IAT in alum 45d elbow after carb bonnet about 10 inch from TB. My air cleaner is down and in front of engine about 4 inch and about 6 inch from radiator. My IAT this morning is like 70-80dF while environmental is 50F cruisuing 50mph.

I think my underhood temps has less affect since I have unused cold air to top of engine due to vette hood ducting that previousy served the air cleaner inlet and a serious air dam at front valence that pushes alot of air to radiator. Plus IAT compensation.

Bones232

Thats what i was looking for. My fueling demand changes drastically the longer the engine runs (presumably from heat). Where you have cosistency day to day, i don't seem to have it minute to minute. It would be like christmas if i could figure out why.

I call them lean spikes as i am unable to adequately compensate for the condition.

RBob

iTrader: (1)

When I see things like this, the first thing I go after is the fuel pressure & delivery. This is what happens to the tune as the fuel pressure varies, and I've seen that a lot. Can you go back to the EBL system? If so get a pressure sensor and log it with the EBL.

RBob.

Bones232

When i was using EBL i did log fuel pressure. I'll see if i can find some old logs. As i recall the fp would vary more under partial load than WOT.

Thinking along similar lines i've replaced the injectors, fuel pump (using submersible fuel line), regulator, fuel lines supply and return, wires to fuel pump and relay.

I've also changed plumbing configurations to the tbi. Currently i'm running a supply and return through my aeromotive VAFPR with a auxiliary port on the pressure side of the reg. going to the TB. I've read the stories about the TBI flow restrictions through the pod and wanted to eliminate that as a problem.

I've also run with and without the vacuum attached to the reg.

Sorry for the puke, this situation has me quite flustered.

Ronny

iTrader: (1)

I am just thinkin out loud. Not saying anything wrong with that BUT. I presume the TB injectors would see the VAC changes OK. But if the injectors needs less fuel for a change in load how could it bleed off the pressure quickly? Would it not need to expell pressure through injector? Fuel is flowing into inj but has no return loop. Obviously you capped off the return on the TB?

I run the Aero 13301 VAFPR. Fuel iline from the pump goes to the 7.4L TB then exits to the Aero then back to tank. One port of Aero contains the FPG and the other leads to N20 solenoid.

Bones232

The regulator still controls the pressure. Everything upstream of the regulator will be at a set pressure as determined by the regulator. When the regulator relieves pressure through the return port, everything upstream will see the pressure reduction. As long as the feed line to the TB is on the pressure side of the regulator, it will see the same pressure as the reg.

Yes i have the return on the TB capped off.

Ronny

iTrader: (1)

I agree. If pressure drops injectors should see drop. Probably instantaneous.

Your point is a good one on the pod restriction. Anyway of proving the presence of a restriction? May need an input to the datlog of the electronic FP sensor. Something I could use when N20 is "on". I have 80 lbs injectors at 26 lbs FP. 20 lbs for engine only the I fiqure 6 lbs FP for N20 fuel. I am at 80% DC with just n/a engine @26 lbs FP. 12.9/1 A/F for PE.

Bones232

If i understand what your saying, your looking for the pressure drop from the inlet of the TBI to the injectors. With my setup i'd most likely connect a pressure guage in place of my cap on the return port of the TBI. With no flow through the return, i would be sensing the pressure within the pod.

Have you run the N2O yet? 50 shot?

Bones232

Well, I was able to dig up a couple of datalogs of my FP.

The first graph shows the FP during a gradual rpm increase to WOT in 3rd. The vacuum was disconnected from the regulator.

The second graph is the FP during idle. the several drops in pressure are from shutting down the engine and restarting it. CTS starts out in the mid 60's degF and ends up at operating temp (190degF) for about 1/2 of the datalog. The IAT starts out about 70degF and ends up at about 150degF by the end of the log. The vacuum was disconnected from the regulator.

The third graph shows a unique log. It was of a 57-59 mph cruise. The vacuum was connected to the regulator.

Ronny

iTrader: (1)

First year was last year. NOS jetting proved to be filthy rich. The chart is for TPI so you have to calc the A/F for 26 lbs vs TPI at 42 lbs. Plus the jets given(12?) require you to balance them to achieve desired result.

This year i rejetted but did not run N20 as I developed a oil foulded plug on cyl #2. Last night I pulled plug #2 and #4 and they both looked dirty. I believe oil accumulation. Both cylinder are 175 psi spot on. I expected #2 to be down on compression? Heads are Edel with about 24K miles on them. Could be guides. I will check again with oil sprayed in both cylinders.

Bones232

Does anyone else have a datalog of their fuel pressure? I'd love to compare notes.

RBob

iTrader: (1)

Here is some data from a TBI set up running a VRFPR.

RBob.

Bones232

Holy Crap! Thats some solid fuel pressure.

So the next logical question is...How do it get my FP to look like that? Can you tell me how the fuel system was set up in the sample data you posted? What are the prime suspects for crappy fuel pressure?

The first thing that comes to my mind is leaks or fuel pump. I've redone my fuel lines probably 3 times over the years. I'm getting pretty good at it. I'm confident the connections are solid as i pressure test each flared fitting i use. I've used a couple different sets of injectors with the same results.

The fuel pump is probably the oldest item in my fuel system (aside from the tank). It was the first thing i changed. Maybe I my pump was "bad out of box".

Ronny

iTrader: (1)

Have you considered running a line to windshield or passanger window and and have passanger witness FP gauge?

I would believe the pressue with a non VAC reg would be pretty consistent as reg being be on return line. Is your spring adequate/matched for the FP you are running?

what mfg vafpr are you using?

Bones232

I can re-create the issue while simply reving the car in the driveway. My fluid filled gage doesn't vary much at all... Which one do i believe?

I have the aeromotive unit (13301). It comes with two different springs. I've played around with both springs. Also used the stock regulator at one point.

What kind of fuel pump are you using?

Ronny

iTrader: (1)

I will presume with vac source disconnected

I use same one as you.

What is your vac source?

Bones232

Yes disconnected.

It's currently tied into one of the ports at the front of the TBI. I've also had it plugged into one of the ports on the intake.

Ronny

iTrader: (1)

I recall one of the ports is ported vacuum and not to be used. But that may have been for my crossfire set up. I dont recall. I dont have a good reason but I tapped into the brass manifold fittng for the brake booster and added a nipple.

RBob

iTrader: (1)

There is both mechanical and electronic filtering of the fuel pressure transducer. Mechanical filtering by using a small orifice (~.040") inline with the fitting at the transducer. Electronic filtering by using a analog low pass on the output prior to data logging it.

Can also use the filtering built into the WUD for that ADC channel to help smooth it. Will likely new a newer version of the WUD for this.

That set up has an external MSD inline pump. Mallory external FPR that is vacuum referenced, which is why the fuel pressure varies with the MAP.

One area I've had issues with is the FPR spring. I have pictures of some graphs here someplace but couldn't find them. Need to use a spring that when set to the proper pressure, there is enough but not too much compression on the spring.

Otherwise the fuel pressure will move around. It appears to move on your graphs, but it is difficult to see due to the pressure sensor picking up the pressure pulses. These are caused by the positive displacement nature of the pump and/or the injectors opening and closing.

RBob.

Bones232

At the time i was using WUD version 2.1f. It had filter value for the fuel pressure transducer, which i had set to 80%.

I just finished reading the ~700 post thread related to driveablility issues due to heat. Presumably as fuel temp increases, driveablility decreases. It appears, of the folks that solved their problem, the last thing they did was change the fuel pump. After reading that, i don't have alot of trust in my fuel pump.

The aeromotive fpr comes with two springs. I've used them both with similar results (maybe both springs not ideal?).

I've often wondered what the relationship between the injector pulses and fuel pump pulses. I was able to put my scope on the pressure transducer and injector to try and see. The first pic is of a low rpm scan. I was surprised how little the fuel pressure ocsillated. I expected larger peaks and valleys. It appears to only be a 2-3psi swing max. I was hoping to see a large dip in pressure with the injector pw smack dab in the middle causing a lean condition. That doesn't seem to be the case.

The second pic is at a medium rpm. the fuel pressure swings are similar to the lower rpm.