Is there anything I can do make my car run richer throughout the rpm range?

[90 GSX]

I want to test a theory of mine. Is there anything I can do to make the computer add more gas? Maybe somehow trick the MAF? I do not have an AFC or anything like that...

 

[xcz504d]

Disconnect your O2 sensor, your fuel trims will go up to 140% in a day or so...

Thats the free way...

Remeber when you re-connect it, disconnect the battery to reset your fuel trims back to default...

 

[Talesin]

Grab an AFPR and bump the fuel pressure up. Or did you mean only the free stuff?

 

[90 GSX]

I was looking for free stuff just to test a theory... is there any other way?

 

[CanadianTSi]

I was looking for free stuff just to test a theory... is there any other way?

What is your Theory?

 

[xcz504d]

What is your Theory?

What he said...

Maybe there is another way to test your theory without blowing lots of carbon out your tail pipe... Helps to know what you're trying to do

 

[90 GSX]

Okay... I figured I'd have to give more of an explanation. I have been trying to work the last kinks out of my car after I swapped in the new engine/tranny. I have this random misfire at idle that gets worse when the car is hot. My o2 voltage on the scanner reads about .87-.89 which is a little lean but I have learned not to rely on o2 voltage. However, the car runs lean enough to give me anywhere from 30-40 counts of knock at WOT (11 psi) and about 12* timing - both of which are unacceptable. The car is built very well and very cleanly. I'm not a newbie and there are no obvious mistakes anywhere. The only conclusion I coule come up with is that the lean condition is being caused by the eprom chip I am using. The Eprom (which I bought from somebody else with an ECU that eventually fully rebuilt) is programmed for 550cc injectors and MAFT. I am running a stock 1g MAF and RC550 injectors, but I am starting to think that the eprom has somehow ignored the intake air temp. and barometer readings from the stock MAF because I have heard that some people program for a MAFT in that way... I just wanted to see if more fuel would help the knock out... any other suggestions or questions??

 

[steve]

So, swap a stock chip back in. That will make you run about 18% richer and answer your question.

Steve

 

[90 GSX]

I don't have a stock chip unfortunately... unless... my stock 90 ECU was an EPROM, can I swap a 90 EPROM into a 91 ECU??? Otherwise I do not have immdiate access to a stock chip. Anybody got a stock 91 EPROM for sale cheap?

 

[JamiesTSI]

I use to hook a 10K resistor into the air temp. wire coming from the MASS. It made the computer think it was 0 degrees all day long. Which in turn richend up the mixture.

 

[xcz504d]

That is alot of knock at 11 PSI especially with 550's... I think you are on a good track with the EPROM... keydiver chips sells custom chips cheaper than a MAF-T, the resistor JamiesTSI posted about is a great idea, just to expand on that thought, maybe try a rheostat (variable resistor) so you can lean and richen right at the MAF... But that may not help you if the chip is set to read his MAF setup and is ignoring yours...

 

[90 GSX]

I use to hook a 10K resistor into the air temp. wire coming from the MASS. It made the computer think it was 0 degrees all day long. Which in turn richend up the mixture.

This is the kind of thing I was looking for... Is this a for sure thing, I mean happens when the sensor warms up? It just reads cooler than it really is?

Another thing I noticed was that my low trim was almost maxed out but the medium and high trims were around 110-120 percent. I'm going to change my plugs today and see if makes a difference.

 

[steve]

I use to hook a 10K resistor into the air temp. wire coming from the MASS. It made the computer think it was 0 degrees all day long.

Since he thinks that the chip he running might be set up for a MAFT with the baro and air temp sensors are ignored and defaults used putting a pot on AIT isn't going to do much.

Steve

 

[90 GSX]

Since he thinks that the chip he running might be set up for a MAFT with the baro and air temp sensors are ignored and defaults used putting a pot on AIT isn't going to do much.

Steve

I came to that same conclusion...

Steve, would that same problem be able explain a random misfire at idle???

 

[steve]

would that same problem be able explain a random misfire at idle???

I don't know. How much of a misfire and how random?
Do you have a datalogger so you can look at the values?

Steve

 

[Spyder50Trim]

if u had 30 counts of true knock.. u would be posting about rebulding...

I assume u have phantom knock... CHeck your knock sensor... What are your injectors at when your getting knock? you can also have a rich knock..


Can you post a log?

 

[90 GSX]

Steve - I have a logger and I do have some logs.

Here is a post of some I took a while ago, nothing has changed since then:

http://dsmtuners.com/forums/showthread.php?t=205372&page=1&pp=25

The misfire is like vvvvvvvvpopvvvpopvvvvvvvvvvvvvvvvvvpop. It truly is random, however, it seems to increase in intensity AND frequency when the car takes a fairly long drive. Almost like it's gargling but the idle stays exactly where it should despite the misfires.

I had an idea. What if I used the resistor idea but on the coolant temp sensor instead of the intake air temp wire. That way the EPROM wouldn't affect it if the IAT and BARO tables are zeroed for the MAFT. What do you think??? If I could what resistance should I use to lower the coolant temp 20 or 30 *C Would it affect any other systems on the car?



Spyder50Trim - I'm not stupid enough to blast the car at WOT getting that much knock so NO I will not be rebuilding. I just got done with a rebuild in fact... Engine pulls about 185 psi across the board compression wise on 2g pistons. Knock sensor is torqued properly.... it is not phantom knock I am 99% sure of that.

It's either a weak fuel pump or the the EPROM thing... I have a Walbro 255 hi pressure at home and a rewire kit but I don't have an AFPR. Anybody got one for sale? Cheap? Or at least knock where I can get one new for a decent price???