Printable Version of Topic

Click here to view this topic in its original format

914World.com _ 914World Garage _ l-jet gurus need input

Posted by: ablose58 Apr 14 2005, 11:55 PM

Thanks in advance for the advice, I have a 74 1.8 l-jet and I just replaced vac hoses intake boots and gaskets/fuel inj seals etc. I also installed an air/fuel mix gauge and the gauge indicates that I am running quite lean also my cyl head temp seems a little high too,around 350f so what's the best way to richen my overall mixture so head temps and air /fuel mix is closer to 14.7 or stoich if you will ? thanks again AL

Posted by: lapuwali Apr 15 2005, 12:15 AM

Where are you running lean? Idle? Midrange? Top-end? All three?

If it's all of the above, look at your fuel pressure, and consider getting your injectors cleaned. If it's only the top-end, how lean is "quite lean"? L-Jet is somewhat known for lean running on top.

Also, what air/fuel gauge are you using to check this, and where do you have the O2 sensor mounted?

CHT of 350f isn't all that high for a stock engine. It's common to see 300f around town, and 350f on the freeway or pulling up a hill.

Posted by: ablose58 Apr 15 2005, 12:21 AM

I am running a nordskog gauge with a matching 02 sensor with an internal heater and it indicates lean conditions all around ,when I changed out my plugs they were very ligh tan in color and all were consistantly the same,the gauge also uses a buffer box too.fuel filter? press reg? aux air valve? I am confused

Posted by: ablose58 Apr 15 2005, 12:23 AM

Oh the o2 sensor is mounted in a monza exh.where all the pipes merge together.thank again AL

Posted by: Reiche Apr 15 2005, 12:27 AM

Al, If you're lean all the time, I would make ablosesolutely sure there are no vacuum leaks anywhere. Then check fuel pressure like lapuwali says.

Posted by: ablose58 Apr 15 2005, 12:36 AM

I've changed out all new vac lines intake boots and manifold gaskets,also could a sticking aux air valve cause this condition>

Posted by: sean_v8_914 Apr 15 2005, 12:40 AM

bypass the aux air valve and test again. how did you check for leaks?

Posted by: Reiche Apr 15 2005, 12:43 AM

Yes, that could do it. It should close within a few minutes of starting up. Easy to check.

It wouldn't hurt to clamp all your new hoses, even with zip-ties.

Posted by: ablose58 Apr 15 2005, 12:47 AM

New hoses were very snug to put on , I suppose I could pick up a vac tester and ck various areas for leakdowns?

Posted by: rhodyguy Apr 15 2005, 05:50 AM

interesting as al's car runs very well and doesn't exibit the symptoms i would associate with running lean. it wasn't poping on decel or anywhere else. double check all the nuts on the intake that had been loosend? how high did the gauge read at it's best al? as lean as it read before i left yesterday, i would think the car wouldn't even run.

k

Posted by: scott thacher Apr 15 2005, 05:51 AM

actually a sticking aar will not cause a lean condition it will cause a high idel. vacumn leaks will, so will low feul pressure but you can not adjust it on a 1.8 it changes with vacumn. to richen it there is a screw on the afm what down in about a 3/8 inch hole you turn that screw in to richen it. but before you do that look for vacumn leaks, take a propane torch turned on and unlite. take the torch around the engine bay to all the hose connections, the idel will go up when/if you find a leak

Posted by: rhodyguy Apr 15 2005, 06:19 AM

al's car is a bit slower to idle down when warm and it doesn't sustain that semi high idle on cold start up. i would put that flapper box you got from monty on al. he told you it came off of a fine running engine. eliminate that possibility in short order. the spark plug electrodes were consistantly med light tan across all 4.

k

Posted by: lapuwali Apr 15 2005, 09:03 AM

That a/f meter sounds like a narrowband unit, though I believe it's one of the more expensive ones. I know this isn't the kind of thing anyone wants to hear, but IMHO, they're fairly worthless, and with the sensor so far from the exhaust ports, I doubt that reading can really be trusted.

Light tan sounds right, the CHTs are about right, and it seems to run nicely. I'll bet you're not lean at all. Find someone with a proper wideband AFR meter, and it will very probably show you're spot on, or perhaps very slightly lean.

Posted by: rhodyguy Apr 15 2005, 09:38 AM

i know al is sleeping. i have an aar valve for him to try. as he stated, he placed his sensor in a position where it reads the exhaust before it gets to the mufflers on the monza, where both pipes merge coming off the h.e.. would the long exhaust run before the sensor/bung cause a misread? is that what you mean james? his car runs very good and delivers fuel milage over 30mpg on the freeway iirc. just a few idle, start up glitches. i've got an aar off of an engine that ran great sitting in the garage for him. the vaccum line kit was a pos. the hose diagram was copied from lined notebook paper. one of my wife's 3rd graders could have done a better job drawing it out too. either the hoses were to lose, or WAY too tight when you put them on the fittings, as in bare down and reef the bastards on.

k

Posted by: lapuwali Apr 15 2005, 10:00 AM

QUOTE (rhodyguy @ Apr 15 2005, 07:38 AM)
i have an aar valve for him to try. as he stated, he placed his sensor in a position where it reads the exhaust before it gets to the mufflers on the monza, where both pipes merge coming off the h.e.. would the long exhaust run before the sensor/bung cause a misread? is that what you mean james? his car runs very good and delivers fuel milage over 30mpg on the freeway iirc. just a few idle, start up glitches.

Yes, the distance from the ports matters. Narrowband O2 sensors have to be HOT to work, and they only read correctly in a fairly narrow temp range. The internal heater helps, but it can't do it all by itself.

The narrowband units are also really just three way switches: lean, spot-on, rich. Any other reading is, frankly, a lie. They have no real way of telling if it's way lean or just a tiny bit lean. This car may be running just a tad lean, which could be fuel pressure, it could be dirty injectors. From the description, it's running too well for it to be running way lean (like lean enough to worry about).

The wideband units have much better heaters in them, and can read accurately even just stuffed into the end of the exhaust pipe (so long as outside air isn't diluting the reading). The best meters (including the Innovate) can also be calibrated at any time to ensure a correct reading.

What are the startup and idle glitches?

Posted by: rhodyguy Apr 15 2005, 10:09 AM

i'm not so sure al does the cold start up as the owners manual states. key off (i think), fully depress gas pedal, release, and turn the key, iirc, i'd have to pull the manual out of the 75' to check. a bit slow to return to a stable 900 or so rpm idle when warm. a little bit of a "hunt". he's obsessing . most guys that had a car that ran as well as his would call it good to go.

k

Posted by: Marty Yeoman Apr 15 2005, 10:10 AM

Try adding a 300 to 500 Ohm resister between the head temperture sensor and the wireing harness.
A 280 Ohm adds about 1% CO.