Possible Lean condition in L-jet motor - HELP, Fuel injection issues Options

[Cupomeat]

Ok, I am having the following problem on my 1.8l Ljet induction 914 motor.

First the basics;
1.9L (96mm big bore kit with KB pistons etc.)
8.4 to 1 CR
1.8 heads built out to 2.0l valve sizing, etc.
Stock fuel injection with adjustable FP regulator turned 15% higher than stock, currently(Pre-Lambda L-Jet, bummer)

Now, the symptoms;
Under normal acceleration, the car runs great and sounds fine, but under prolonged full throttle, the engine heat seems to go way up and pinging occurs. No pinging ever happens when I am rowing through the lower gears, but only seems to happen in 5th gear after prolonged Wide Open throttle (WOT).

So, my assumptions;
1. The car is going lean at prolonged WOT resulting in high head temps and pinging.
2. Ignition timing does not seem to play a role in this as I've played around with retarding the timing to decrease the pinging, but it never goes away at Prolonged WOT.

My plan;
1. Buy a WB Fuel/air ratio gauge and weld in the bung for the 02 sensor to support my theory

2. I have an inline fuel pressure gauge in the engine compartment, but can't watch it when I drive the car, especially in 5th gear at WOT (for very long, LOL)

3. Check to make sure the throttle switch is working to trigger WOT

4. If #3 is fine, is it possibly the fuel pump is running out of pressure?

5. I am also going to install a remote oil cooler to try to bring the heat down, but on a mild 1.9l, it seems excessive, especially as I probably have about 85 hp.

6.Probably install a cyl head temp gauge to try to pinpoint temps besides oil.

7In the end, if I have to pay for Dyno time to get to the bottom of this, I will but I'd rather not spend that yet.

Anything else people can think of? Any help/thoughts would be appreciated.

Eric

[Cap'n Krusty]

You DO understant the L jet engine uses a "rising rate" fuel pressure regulator, right? That means the fuel pressure rises under load (AKA "demand") If you have a set fuel pressure at idle, it won't meet the demand under load. That'll make it lean out. Tied to the rather high CR (high for current fuel in street driving conditions) will make it ping and become hot.

The Cap'n

[Cupomeat]

Yes, thanks, you are correct.

The "rising rate" fuel pressure regulator regulates the delta of fuel pressure (injector) to manifold pressure so you are effectively setting the pressure differential to manifold.

At idle, the manifold pressure is partial vacuum (0.4 Bar), which would necessitate a lower effective fuel rail pressure to maintain the same delta. At WOT, the pressure must increase in the fuel rail to allow for the same delta when the manifold pressure rises closer to atmospheric (0.8 Bar).

I set the fuel pressure, as per spec with the vacuum line removed from the Fuel Pressure regulator, therefore effectively setting the pressure at atmosphere or 1 bar.

It is from this spec that I increased the current Fuel pressure.

I have a fuel pressure gauge in line on the engine, so I can monitor that pressure at idle, and very quick WOT. For brief bursts (as I am not driving or on a dyno yet.) the Fuel pressure is correct.

Once I get a A/F ratio gauge installed, I'll have more to go on.

Thanks and I've read quite a bit of your responses, thanks for being so active in this community.

eric

You DO understant the L jet engine uses a "rising rate" fuel pressure regulator, right? That means the fuel pressure rises under load (AKA "demand") If you have a set fuel pressure at idle, it won't meet the demand under load. That'll make it lean out. Tied to the rather high CR (high for current fuel in street driving conditions) will make it ping and become hot.

The Cap'n

[Brando]

First you have to determine if it's fuel or ignition... the WBO2 sensor will help you figure that out with an A:F ratio.

If you know your timing is good then no worries there...

L-Jet does use a rising-rate FPR as the captain said. When using stock 1.8 components (injectors, CHT, AFS, FPR, etc) and going up in displacement you might have to adjust the air flow sensor to give more fuel. Again, you need a WBO2 to check and set this right. AFAIK when you hit the 2.0 liter mark you should go up to 912E injectors as they flow more than stock 1.8 injectors.

With the change in compression you might want to try a bit higher octane fuel... Maybe 89 if you used 87, 91 if you used 89... etc and see if that helps with the pinging.

[Cupomeat]

Thanks,

As for fuel octane, I always run 93 since I first experienced the issue so I believe I can rule that out given the reasonable CR ratio (IMHO).

Also, as per the Bosch book, the Air Flow meter only affects mixture up until about 3500 rpm and then it is all about mapping on the analog FI brain based on RPM and the throttle position sensor. As the TPS has only 3 possible circuits, clearly it is not a high accuracy fuel metering at high RPMs. I will try the enrichment of the AFC once I get my WBO2 sensor if the problem exists as low RPM also.

I'll go the WB02 route but I was looking to see if anyone experienced this before, and if so, any possible explanations.

In my mind, the following are possible
1. The fuel pump runs out of pressure at sustained WOT
2. The TPS is not triggering full enrichment or another component/wiring is failing to make a difference
3. The Fuel filter is clogged (doubtful)
4. the whole setup isn't delivering enough fuel all along.


Another thing I've found is that the car sometimes starts to miss at redline. I do not have a rev limiter in it and there appears to be no rev limiter built into the AFC analog computer. Possibly this is related?

Also, the car doesn't idle very well if you rev and let it drop down. It will idle fine if you don't blip the throttle. I have verified that there are no intake leaks so I am obviously looking at something else here. Possibly this is related?

Just trying to follow the scooby doo path of finding clues to who is the ghost in the machine. (doubt this one is Old Man withers from the Carnival)

Thanks again for helping me think this one through.

[Brando]

You can rule out #'s 1 and 2.

The fuel pump for L-Jet puts out more than enough pressure. Without a FPR on there it can go above 50psi easy.

TPS has 2 circuits... Open (throttle closed) and closed (throttle open). When closed the ECU meters fuel according to the AFS (under 3500 rpm) or fixed values (above 3500 rpm). When open the ECU runs on the idle circuit - for 76 version of L-Jet it cut fuel via the injectors on deceleration until a certain RPM (1500? 1800? 2000?) and then kick back in, saves fuel and provides quicker deceleration or something.

If you have a blockage that'll create a lean issue. Have you had the injectors cleaned? www.witchhunterperformance.com does it for fairly cheap.

#3: When diagnosing fuel delivery problems and you have no idea the last time your filter was changed --if ever-- it's probably a good time to change it and continue diagnosing. Clogged filter can greatly effect your fuel pressure.

#4 - What you're trying to diagnose and/or fix.

Another thing to check... Are you using points? They're only good until about 5000 RPMs and then you might experience "floating points". This will give you that rev-limiter effect. I've tried different brands and BOSCH is the only way to go for these. Get the better points with the foam block. Remember to lube the cam lobes of the distributor shaft with the special grease. If using the stock ignition system set the gap and dwell accordingly or the injection system will have issues as well and then you'll be confused if it's ignition or injection or both. Chasing gremlins that don't really exist.

I overcame the dwell/gap issue by switching to a Mallory Hyfire system with the better (solid state) tach/EFI adapter and adjusted the points to a smaller gap. It doesn't use the points to build up a charge in the coil so I have almost no gap and no floating points issues.

[toon1]

In your case ( as most ) an 02 sensor WILL be benificial.

you have increased the CC or CI displacement of the engine and the F.I system is not desined to hadle it.

ALTHOUGH, you HAVE increased the F.P. to try and compensate.

15% over stock pressure is about 4 P.S.I. correct? that's about 40cc/min. increase in flow.

Did you do some calcs. to see if that will be enough?

Here's one thing to think of:

1) you have increased the size of the pistons
2) you have increased the size of the valves.

This will create MORE demands for air flow into the motor which should require a bigger TB.

The TB may be too small for sustained high rpm's. When the air intake of a motor is too small, at sustained high rpm's (WOT), the vac. signal; will actually raise(more vac.) as the engine is trying to pull more air that it's getting.

If this is what's giong on, you may see a slight DROP in F.P. because there is VAC. being reapplied to the engine.

it sounds like you have a VAC. gauge. If so it would be easy to do a test.

Keith

[ChrisFoley]

The only place I know of in the northeast where you can hold WOT in 5th for any length of time is Pocono. If you're spending a lot of time at WOT you should consider having EGTs on all 4 cylinders.

[Katmanken]

And the other dumb thing to look for is air leaks......

With an air leak, the air flap will mis-measure the amount of incoming air and will signal a lower air flow to the brainbox resulting in reduced gas injection, lean conditions, and overheating....

Ken

[r_towle]

The only place I know of in the northeast where you can hold WOT in 5th for any length of time is Pocono. If you're spending a lot of time at WOT you should consider having EGTs on all 4 cylinders.

Rt 91s at 3am-5am

[r_towle]

I wrote a long reply..but my internet died before it posted.

Simple a sweet.

Dizzy advance plates need to be cleaned
Check dwell at idle and watch it while you rev it...if it changes, your dizzy bushings are worn out.

AFR can be adjusted, the old spring can be tightened, but dont bother if the issue is higher than 3k

Air leaks
Oil filler cap, a gasket and o-ring (If you find them new, let me know)
Oil filler base gasket
These three items are often overlooked and cause a serious headache.

Lastly, check the large intake hose for cracks on the bottom..use a light and bend the hose every which way to see if its cracked.

Rich

[Cupomeat]

The only place I know of in the northeast where you can hold WOT in 5th for any length of time is Pocono. If you're spending a lot of time at WOT you should consider having EGTs on all 4 cylinders.

Yes, Pocono was where I first noticed it. I think westach sells a Cyl Head gauge for 4 cylinders. Might be the thing for me to buy, or do you recommend a EGT instead?

[Cupomeat]

And the other dumb thing to look for is air leaks......

With an air leak, the air flap will mis-measure the amount of incoming air and will signal a lower air flow to the brainbox resulting in reduced gas injection, lean conditions, and overheating....

Ken

Yes, I think I've ruled this out because the pinging occurs at RPMs above what the AFC flap controls. I've been over the engine many times looking for leaks and attached a vacuum gauge which seems to say that I don't have any noticeable ones.

[Cupomeat]

In your case ( as most ) an 02 sensor WILL be benificial.

you have increased the CC or CI displacement of the engine and the F.I system is not desined to hadle it.

ALTHOUGH, you HAVE increased the F.P. to try and compensate.

15% over stock pressure is about 4 P.S.I. correct? that's about 40cc/min. increase in flow.

Did you do some calcs. to see if that will be enough?

Here's one thing to think of:

1) you have increased the size of the pistons
2) you have increased the size of the valves.

This will create MORE demands for air flow into the motor which should require a bigger TB.

The TB may be too small for sustained high rpm's. When the air intake of a motor is too small, at sustained high rpm's (WOT), the vac. signal; will actually raise(more vac.) as the engine is trying to pull more air that it's getting.

If this is what's giong on, you may see a slight DROP in F.P. because there is VAC. being reapplied to the engine.

it sounds like you have a VAC. gauge. If so it would be easy to do a test.

Keith

My calculations for increasing the fuel pressure were based on overall displacement increase, but that unfortunately should cause the engine to run rich as lower RPM (while under the AFC flapper box ) control and then right on in the upper RPMs.

Time to calculate a little more.

Hmmm, very interesting, so if at WOT, at say, perhaps 4500, the airflow exceeds the amount of air the TB can flow, it will start to actually increase the partial vacuum until redline.

This would in-fact lower the fuel pressure and run lean... but would not the fuel pressure drop actually preserve the fuel pressure to manifold pressure delta? The Rising Rate fule pressure regulator should maintain a constant pressure delta between manifold and fuel rail pressure. With a partial vacuum, or an increase in vacuum the pressure delta would be the same and it would not make any difference.

Hmmm, OK, now I need to buy a WBO2 gauge, a cyl head temp gauge (4) and a manifold vacuum gauge.

Looks like I'll need more dashboard, LOL!

Great theory, I'll see if I can support it by the instruments.

[Cupomeat]

I wrote a long reply..but my internet died before it posted.

Simple a sweet.

Dizzy advance plates need to be cleaned
Check dwell at idle and watch it while you rev it...if it changes, your dizzy bushings are worn out.

AFR can be adjusted, the old spring can be tightened, but dont bother if the issue is higher than 3k

Air leaks
Oil filler cap, a gasket and o-ring (If you find them new, let me know)
Oil filler base gasket
These three items are often overlooked and cause a serious headache.

Lastly, check the large intake hose for cracks on the bottom..use a light and bend the hose every which way to see if its cracked.

Rich

Sorry to hear of the passing of your internet, I hope you can move on quickly and live a full life in its memory! (IMG:style_emoticons/default/biggrin.gif)

Yes, the dist is a new Mallory Unilite with vacuum advance (optical pickup) and the issue is higher than 3k, always.

I'll go through the engine again looking for air leaks as I know they plague these L-Jets.

Thank you!