Fuel Injection Question

Russe11

Russe11

True Classic
My car is an '81 (fuel injected 1500) and I'm hoping for a little help sorting an issue that I believe is a Fuel Injection problem. The symptom is that it runs rough at 2000-2500 RPM under light load. It runs smoothly higher and lower, and through this range when the throttle is open farther. It seems like it's running lean when it exhibits the problem.

We've gone through this FI Tuneup Procedure: [FONT=&quot]http://www.mirafiori.com/faq/fiatFI_may2002.pdf including checking the resistance values from the AFM at the connection to the computer (which were all "OK" according to the guide).

Running the engine in the troublesome range in the shop, we can smooth it out by pushing the flap on the AFM open a little further, which should fool the computer into telling the injectors to deliver more fuel.

Any suggestions?

Thanks,

Brian
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any pre-ignition symptoms? Try disconnecting the vac advance line to the distributor, pull it off the plenum, bottom where the throttle plate lives and cap the nipple. My '81 seems to like having that inop.
 
Look carefully at the vacuum hoses, small and large (main air hose), for leaks, loose fit, cracks.

Three things affect the mixture; the AFM, the Temp Sensor II, and the O2 sensor. I assume you ohm tested the Temp Sensor II. Check throttle position switch setting. The O2 sensor is the last thing that will affect running, but is usually more temperature related rather than throttle related, unless the TPS is not set right.

Fuel pressure can also affect the mixture, so make sure the vacuum hoses to the distributor and the Fuel Pressure Regulator are on the correct nipples, sometimes they get reversed. The one for the vacuum advance module on the distributor goes to the nipple on the throttle body, while the FPR goes to the intake manifold.
 
no knocking

Hi Jeff,

Thanks for the reply. Didn't hear any knocking, but I'll check running it with the hose to the vacuum advance plugged.

Brian
 
Sensors

Hi Greg,

Thank you for the reply.
Yes, the temperature sensor was in spec, too. (255 ohms at 180 deg indicated). We re-set the Throttle Position Switch per the manual, and the O2 Sensor is new.

I've been looking for air leaks,but haven't found any yet. I'll double check the hose routing, as you suggested.

Brian
 
Brian... TWO things...

1. Do as Greg suggests only use an UNLIT propane torch or WD40 to find the vacuum leak. Carefully and slowly move the torch or spray on the hoses while the engine idles... and if the engine speeds up, you have an vacuum leak.

2. If this doesn't fix it... I'm betting on the injectors themselves. Remove and have them PROFESSIONALLY tested, cleaned, and/or replaced. They usually send before and after test fotos and worth every cent of 60 to 120 bucks... Ask here in a new thread for referrals.
 
Thanks, Tony

Thank you, Tony.

I'd seen your suggestion of testing for leaks with a propane torch in other threads, so I tried it. I also pulled the vacuum line off the distributor and let it sniff the end of the torch, to get an idea of how much acceleration you are talking about. It seems like a good diagnostic technique, but it didn't turn anything up so far. (I'll try it again.)

The injectors were purchased from a forum member, and were professionally cleaned. The fuel lines & filters are new. The fuel tank was removed/cleaned/lined by the previous owner during his attempt to get it running.

Thanks for the suggestions. I welcome any pointers you care to give.

Brian
 
the distributor vacuum line wont' see anything at idle, it's just off idle (as throttle plate opens) that is sees vacuum
 
AFM

Thanks for the suggestion. I don't have a spare AFM on hand, but will see if I can scare one up. Is it possible to lighten the spring on the flap so it'll move a little further for a given airflow? It really seemed to smooth out with just opening it a little more ...
 
Hmmm

Hmmm... That's interesting...
I definitely felt vacuum on that line when I pulled it off & put my finger over the end. Perhaps this is pointing to having the lines swapped as Greg suggested. I definitely have to check that.

Thanks!
 
the throttle plate should close off that port at idle, if I understand it correctly, is your TPS (throttle plate sensor) adjusted correctly (loosen and turn until it clicks, tighten back up)?
swapped lines, hmmmmm
 
I'll check...

The TPS is set according to the FI Troubleshooting guide: 0 ohms between Terminals 2 & 18 when the throttle closes, and the circuit opens as soon as the throttle does.

I'll have to check the hose routing on the car, which is at my father's house. I'll be over there again on Monday. Working on bookkeeping for my business today:pc:
 
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Did you pull the line off the distributor and felt vacuum? I don't think you should at idle. Yep, check those hoses!
The TPS ohm procedure is spot on but I think simply listening for the click gives the same results. I take it from your sig you're doing the car in Bronze? I did my motorcycle in bronze, and the logo for my X. I'm anxious to see it. I always thought that would be a good color on an X.
 
bronze

Yes, I felt vacuum on the dizzy line at idle. Any chance you can point me to a diagram indicating that port should be blocked off, then?

Here's a picture from when we first got it back together after paint.
http://xwebforums.com/forum/index.php?posts/207393#poststop/
There's going to be some re-work on the paint job, but we learned a lot in the process. There are in-progress photos a couple posts up. It already looks a lot better than the "UPS Brown" that was on it before.

Now we just need to sort out a few things, although I'm thinking my signature line may say "Almost ready" for a while...
 
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Hmmm again

Thanks for the link to the diagram. I'm certain the line to the fuel pressure regulator is in the right place. That looks like the only likely one to be switched with the vacuum advance, so I'm doubtful that's it, but I'll be double checking on Monday, anyway.

Brian
 
Update

My father & I spent some time working on the car last night.

We verified that the vacuum hoses were all routed properly, as Greg suggested.

We verified that the vacuum advance diaphragm on the distributor wasn't leaking. It would hold a vacuum well.

Then we plugged the line from the plenum to the distributor, (as Jeff suggested) and tested it. It ran much more smoothly with the vacuum advance disabled.

We took the distributor out to check for radial play in the bearings or other signs of distress, and found nothing. Tested the pickup coil in it, and found it to be in spec.

Any suggestions about what could be going on with a distributor that pushing on the AFM Flap can fix/mask?

Thanks for any suggestions,

Brian
 
The timing could be too far advanced. You mentioned the vacuum advance line had a vacuum signal at idle, this suggests the throttle-stop is incorrect, and has to be reset. Often this is caused by a well-meaning but uninformed person adjusting the idle speed using the throttle-stop screw rather than the idle-air screw (17mm locknut) on the top of the throttle body.

To adjust, run the engine to normal temp. Make sure there is a bit of slack in the throttle cable and therefore it's not holding the throttle open. Screw idle air screw in until it seats. Loosen idle stop screw locknut, adjust until the idle is 800-900 rpm. Tighten throttle stop screw locknut. Adjust idle air screw until desired idle speed is achieved.

The TPS may need to be adjusted as well to achieve this. If the TPS is not set correctly, the ECU will try to use O2 sensor feedback to adjust the mixture at idle, and will not run smoothly. With the engine off, you should be able to hear an audible click at the TPS when the throttle is opened slightly. It should be consistent and always click when the throttle closes as well, adjust until it does.
 
Thanks Greg

Thank you, Greg.

We adjusted the idle as you describe, following the procedure in the manual, but will run through the procedure again to verify it. (And I'll double check the vacuum at idle that I observed before.)

I'll report any findings after our next work session (Friday night).

I welcome other suggestions, too.

Brian
 
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