new b here with obd1 tuning ?s

[badluck]

Hello everyone.I'm hoping to find some help. I purchased a 84 jeep with a 258 and mopar injection.Runs well except for a little ping and high nox. I've had several mechanics look at it and everyone says I can fix it. Not.The nox are about 1200. The rest is great. New cat and its working correctly and its the correct 1,new 02 sensor from mopar,temp,map,correct valve cover,timing,tried 99oct fuel, comp was within 2% accross the board,no exhaut leaks,new fuel pump,5.0 injectors, adj regulator.The nox always stays the same. The fuel curve reads -5% hence the high nox.I've raised the fuel pressure till it stalls the motor idling at 44 psi nothing works. I thought the computer was bad and put in a stock 95 computer it also said-5% fuel curve. The 95 had more timing in it and nox went to 2300. I've injected propane and nox goes to 0. The lambda calc proves it's running lean.WTF? I've been trying to solve it for 5 years now.I've heard a map adjuster only helps when the engine is cold or under heavy throtle. is this correct? Can anyone reprogram the computer? Any help would be great.

[Cheromaniac]

Hello everyone.I'm hoping to find some help. I purchased a 84 jeep with a 258 and mopar injection.Runs well except for a little ping and high nox. I've had several mechanics look at it and everyone says I can fix it. Not.The nox are about 1200. The rest is great. New cat and its working correctly and its the correct 1,new 02 sensor from mopar,temp,map,correct valve cover,timing,tried 99oct fuel, comp was within 2% accross the board,no exhaut leaks,new fuel pump,5.0 injectors, adj regulator.The nox always stays the same. The fuel curve reads -5% hence the high nox.I've raised the fuel pressure till it stalls the motor idling at 44 psi nothing works. I thought the computer was bad and put in a stock 95 computer it also said-5% fuel curve. The 95 had more timing in it and nox went to 2300. I've injected propane and nox goes to 0. The lambda calc proves it's running lean.WTF? I've been trying to solve it for 5 years now.I've heard a map adjuster only helps when the engine is cold or under heavy throtle. is this correct?

Yes. The MAP adjuster will only work when the ECU is in open loop mode.

Can anyone reprogram the computer?

Unfortunately no. The OBD 1 ECU cannot be reprogrammed. Raising the fuel pressure should have corrected the lean condition, so I wonder whether there's a problem in your O2 sensor or its wiring harness causing it to output near 1.0v all the time (and thus commanding the ECU to keep pulling out fuel).

[badluck]

How do I check that? Trace a wire back to the ecu checking the voltage? Which wire? What should the voltage read? Is it normal for the scanner to read -5% all the time?

[Cheromaniac]

How do I check that? Trace a wire back to the ecu checking the voltage?

Yes.

Which wire?

If you have a 4-wire O2 sensor (white, white, grey, black) the signal wire to the ECU will be the black one.



What should the voltage read?

0.0 (extreme lean) to 1.0v (extreme rich). At idle it should fluctuate either side of 0.5v (stoich) on a warm engine.

Is it normal for the scanner to read -5% all the time?

No. Your engine's running lean.

[badluck]

It's a 2 wire out of the o2 sensor. I've tried several o2 sensors. I like where your headed here.

[christuned]

I am going to clarify a few things here:

#1 -5% is ok, it does not mean that the engine is running lean, it just means that the ecu is pulling 5% fuel over it's base fuel calculation to average lambda 1 based on the O2 sensor. Also, when you say -5%, is that the long term fuel trim, or the short term fuel trim. The short term fuel trim will always toggle to maintain lambda 1 (stoic) , so it should increase-decrease-increase-decrease. The narrow band O2 sensor only reads accurately at lambda 1 , at lambda 1 it reads about .45 volts. Since .45 is a known quantity, the ecu , when in closed loop, will push the fuel trim up until the voltage crosses above .45 volts, as soon as it crosses above .45 volts the ecu will then push the fuel trim negative, until the voltage drops below .45 volts, and this cycle just repeats itself.

Chrysler OBD1 computers can be tuned, some of them were even flashable, although all the Jeep SBEC2's I've seen have UV chips in them, which means socketing the ecu. I've tuned OBD1 Jeep ecus, they are not fun, or nearly as flexible as the later JTEC's, but the timing is not too bad. No need to tune the ecu though, you can globally adjust the ignition timing if you can find someone with a DRB2 or DRB3, there is a timing offset available on pre OBD2 Chrysler ecus.

[badluck]

Thanks for the explanation.So if it is always -5% and the lambda is about1.1 could the voltage be over .45 sending the fuel curve into the negative? Example on the dyno it never changed from -5%.It did not matter if I was on the gas or off I even pulled a vacuum line and nothing changed.I checked the o2 and it is a 4 wire.

[christuned]

With what scan tool are you checking this fuel trim value?

Are you looking at the :

Long term fuel trim?

or

Short term fuel trim?

or

Addative fuel trim ?

[badluck]

Not sure about long or short. It was a mt2500.

[atias]

chris is that a stock obd1 sbec2 timing map?

[christuned]

yes, that is a stock SBEC2 timing map.

the snap-on scan tool should be able to give you all of those logging parameters. Do you have access to the scan tool or is that information coming from your mechanic?

[christuned]

Btw, the MAP sensor is always used, when in open loop the O2 sensor is ignored, not the map sensor.

[atias]

is there any variations in the timing map between the sbec 2 ecu models? or the timing is all the same?
i'm asking this because i have 3 different jeep sbec 2 ecu's and they are not all workings the same.
and if so can you please post a pictures of the maps.
those timing maps can really help us AEM FIC users to know what the stock ecu is doing.

[badluck]

I ran the test w/the mechanic. What would cause it to run lean? It is actually 1.05 on lambda calc while running smog test.

[christuned]

Ok, so you are not referring to fuel trim, you are referring to measured lambda ? If you have emissions measurement then post those:

HC

CO

CO2

O2

NOx