Fuel cutting on WOT,

abec

abec

Wil
This is on a 86 Bertone EFI 1500, w/ big valves, 10.5:1 compression, stock cams.

So I am having some issues at wile driving during WOT, when I get to 6k it fuel cuts and surges. It will go past 6k under partial throttle, and when there is no load on the engine, but not under WOT.

I checked for vacuum leaks, replaced fuel filter, checked TPS (unplugged it and still had the same issues) made sure that the tach was reading properly, and I beat it with a hammer. Nothing so far has helped.
 
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Question, what did you do to richen the mixture for the additional fuel required by the extra airflow? I'm wondering if you're running lean. 2nd thought, is timing correct, idle and at 3000-3500? 3rd thought, find a bigger hammer...
 
cars on 91, and the timing is good (but ill have it tripple checked)

The EFI is stock, my understanding is that the stock efi system should be able to handle the added power.
 
From what I remember, the oe bosch L-Jet are set up to run for economy and emissions, and my air fuel indicated it running on the lean side of the spectrum. This was on an '81. I think if you wired in a cheap air/fuel gauge (single wire), you'd see the same. Running part throttle and in neutral require less fuel than under load. That's my guess.

Anyone else?
 
My bet is that your 'tach' signal wire to the ECU (connected to the "-" side of the coil) is not tight. This is the only connection to the fuel ECU and determines if and when to squirt fuel. On an X, these are stretched tight and the spade connector can come loose over time. I would check to see if this this wire (black sheath w/ a yellow sheilded wire inside) is strained and that the connector is TIGHT.

Another thing to check is that the TPS actually signals a 'wide open' condition. Check to see if the swtich closes (between the center and one outside connectors) when the throttle is opened to about 80~90%. If the switch is bad, you will run in 'closed loop' mode and the O2 sensor will try to correct the mixture back to 'stoich' - and FIATs under full load don't like this mixture...
 
ill get an air fuel meter and see, i was planning on getting one anyways. The wires on the coil are all well connected. I still somewhat suspect the TPS but am unsure how to check, seeing how I tried with it unplugged and got the same results. Telling me that either it is not working, or it is working and has nothing to do with the issue.

Any other idea's?
 
video

[ame="http://www.youtube.com/watch?v=U_s9qXmDgHs&feature=channel_page"]YouTube - fuelcut[/ame]

Decided to use my laptop webcam to video the issue in 2nd and 3rd gear.
 
Fuel Pressure?

Do you have a gauge on the fuel rail, possibly the pressure is dropping off at WOT, Fuel Filter new?

Pump worn? Put a gauge on it.

TonyK.

Grimsby Ontario Canada.
 
Hey Wil...

If ya run it up to the "miss" and then try to go beyond it... does it every clear up or does it just continue to buck?

(You do have plenty of "rev-room" left... so you won't hurt it... try it and let me know...)

It does appear to occur at the very SAME rpm which would lead me to believe its more of an ELECTRICAL issue rather than a FUEL issue. Not sure though...

Also... did you drop and read the FI troubleshooting guide... It may have some hints that can help you to DIVIDE and CONQUER!
 
Sounds like a fuel filter. I change mine yearly. Every winter we get crappy gas that also loosens gunk in the tank. Car runs not so great through the winter and then in the spring I change the filter.

In a car needing peak flow, a partially clogged filter would do as you describe. At WOT at 6K, you're close to full cycle on your injectors. Anything less than full flow through your rail will show itself.

If it was ignition related, the tach needle would falter or drop to zero. With a fuel issue the stumble is felt and not seen, unless it cuts out completely then the engine will rev down slowly as the fuel pressure is consumed over a short time.
 
Similar issue

I'm having similar issue with my dual 40. Will try to change the fuel filter to see if resolve the issue
 
Tony, it wont rev past that spot. It just keeps bouncing the revs right there.

When I open the throttle I hear the TPS click once when I first start turning and no other clicks after, should there be a second click near WOT? I did manage to lower my idle when I fiddled with the TPS, so it appears to be doing something.
 
Do you have the manual?

It is hosted online here:http://www.midwesternmedicalmachine.com/~damonfg/X_FSM/FSM_index.html

For this, you want the section 10-91.

The switch is "closed" when the throttle is closed. The 2 pins (2 and 18) on the switch that are used are toward the front of the car. If you put a VOM on those two pins, it should read zero resistance when the throttle is closed. Just slightly open the throttle and they should read infinite resistance (open). The Fiat L-jet does not use the other pin nor does it register WOT.
 
beg to differ..

Greg, the L-jet in the FIATs do in fact use the WOT at pins 3&18 on the TPS. There is no microswitch inside, so no 'click' but it should read continuity at about 90% throttle opening.
 
Well, if you say so, the manual doesn't reference a test for that.

:blackeye:

I know on my L-Jet VW Vanagon it did, but since the X factory manual didn't test it, I figured it didn't use those pins. My bad.

And you're right, there is no "click" at WOT, but I didn't test pins 3 & 18, doh!
 
OK Wil... I gotta bow out... but listen to Greg and John...

... and get the reference material if you don't have it. Its the only way yur gonna resolve this.

I'm sure they will be "happy" to forward it to you... but the FIAT TS Guide I spoke of is a good start.

Now say the words and do the following: "I downloaded it and read it"... and you'll do much better.

Sorry I can't help anymore, as this goes beyond my expertise... but Greg and John are two of the finest on this subject and this is no time for any ARTISTIC or POETIC LICENSE. Its time to get in step and follow specific rules.

Good luck and stay in touch...
 
I had some JPG's of the service manual, but the quality of those PDF's are much better. I just wish it was all one PDF so i didn't have to download section by section. Ive been busy with school work if I have some free time this weekend I'll test the TPS, as well as get the A/F gauge working.
 
Well... If a test of the TPS doesn't do it...

Then putting off the inevitable of not downloading the manual will only set you back.

This will NOT be the last time you'll need it...

I read the entire FI Trouble shooting manual and found a pattern and a sequence of fault location in a progressive manner that PROVES or DISPROVES componants that will tend to keep you from going in circles or buying non-returnable parts that don't solve the problem.

Your choice...

Enjoy your homework!
 
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