I was running crazy lean...., scientific conclusion = DAPO Options

[drewvw]

Now that I have a trusty A/F meter and about 3 million plug and play resistors in my set. I set out to do some major testing with my buddy this past weekend.


Test:

1) Pop in resistor
2) Get car warm and hit highway
3) Navigator reads meter
4) check plugs, smell exhaust, etc


So we started at 150 and ran all the way up to 1360 ohms. Obviously 1360 was WAY too rich but it represented the ceiling of our test.

I think I have it pretty close now to where I want it, and the wierd stumbling in the cold and erratic running are all but gone.

Some thoughts/conclusions/questions:

Although its probably been 10-12K miles (over 10 years), the PO was running the engine crazy lean for the entire time (as in 16:1 - 17:1 range).

Engine runs fine but it has me thinking about what this did to the lifespan of it.

Aside from the heavy porting of the 1.7 heads and SSI, I am now sort of thinking there was a different cam put in there...which is contributing to the very lean tendencies this engine seems to have.


That's all for now, going to watch the plugs for a bit and monitor things, but it looks like things are in good shape.

Thanks for reading!

[ptravnic]

In my newfound religious beliefs I think you are lucky to have not burned a valve... I hear that can happen when you run the too lean for too long... (IMG:style_emoticons/default/barf.gif)

[fitsbain]

Drew -

Though I havn't had much (any cept for your car) experience riding in or driveing a teener, I was thinking that your car had a lot of kick for a 90 hourse 2000 lb car. My old Z28 was 280 hourse and 3200 lbs and I thoughht your car flet equally powerful.

With that in mind I think your cam Idea may be true.

Also look for Air leaks that are causing the lean condition.

[drewvw]

thanks man!

It definitely runs well and I have checked for air leaks but i will keep working at it. More than one person has told me the car doesn't feel like 1.7.

[r_towle]

I bet you have the motor you are gonna build...

I think its a 1911 or whatever that size is..it sure feel like it..and I have a 1.7 and 1.8..

I think you need to build a BIGGER motor this winter...

Rich

[CoolAirVw]

Tell me more. Newbie here and I dont understand "sticking a resistor in it".

Are you putting one resister in line with each injector?? stock injection? Aftermarket adjustable injection with one resistor ajusting the injectors?

aftermarket TBI? HELP! I dont understand!

(maybe some previous post that I never read explains what you have??)

[Bleyseng]

I think he is adding them to the CHT.

[r_towle]

yup, Drew is having PC difficulties this week...so in his stead...

He got a motor that was a rebuiklt 1.7 liter with the stock FI system installed.
the motor is rebuilt...possibly ported heads , possibly bigger cylinder etc...no real way to tell till it gets opened up...

So this all started with his issue of the car bucking , but only when it was cold out...he has tested every part of the FI system per the very cool web site of Brad Anders on the renn list...we refer to it as the bible...of Djet...

Anways..the whole system checked out..
it still ran like crap.
He bought a used MPS,,,holds a vacuum etc...still ran like crap...

He finally broke down and bought an Air Fuel guage with an O2 sensor, and mounted it on his exhaust system...

then he knew how lean he was running..like 16 :1
it was bad lean

so, he found a bunch of resistors, and made up some pretty cool plug and play modules to put inline with the CHT..that is, unplug the CHT, and plug in the resistor, plug the feed for the CHT into the other side of the resistor..

this tricks the computer into thinking that its cold out, and therefore enrichening the system ..
So, it amkes it run richer,,,more ohms, run richer...

hes a smart guy..read alot about the ranges etc..then got it all working..

rich

[McMark]

Air leaks on D-Jet don't lead to lean conditions like it does on other FI systems (broad overview). Air leaks just change the vacuum signal the MPS reads, which can lead to odd running, but not necessarily lean conditions.

Nice to hear the O2 sensor worked well for you. Sounds like a good time. (IMG:style_emoticons/default/driving.gif)