mbomberz1

Hi all of you guys with your 'new' trucks

For any of you who are supercharged and pay attention to your fuel trims, what generally do your numbers look like?

I have had a supercharged 5vz in my 88 for almost 2 years now. Running great! My fuel trims are within normal limits but do tend to hover in the +7-12% range average. Just curious if this tendency could at all be related to the supercharger. I have not been able to locate any vacuum leaks. Also have a new fuel pump and clean injectors. Doesnt lean out when i get on it and its nothing really that I am too concerned with but it does make me wonder every time I look down and see those little + numbers..

Thanks for any input you may have.

Kolton5543

As you said, the are within reasonable limits but 12% is a little on the high side. I've never work on a SC rig so I have no idea of the regular trims. Most cases when trims start to climb under all load conditions it has to deal with slightly low fuel pressure or dirty MAF sensor. Do you have a aftermarket intake? The oiled air filters often will dirty a MAF real quick. It is always possible that thhe O2 sensors aren't as accurate as they used to be. They do tend to wear out and really should be changed every 100k or so.

mbomberz1

Heya Kolton,

I appreciate the reply. When I did the swap I put in a new Denso MAF and o2 sensors, so that is less likely the culprit but still possible I got a bad one. Using the stock air box and toyota filter too.

I have tried watching my trims while at idle vs increasing and holding the RPMs up to 3500 rpm or so. Seems like they do go down slightly overall but not dramatically. I have also tried using propane to check for idle changes, but I must not be doing it right, because even putting the unlit torch right at the intake I can't detect any RPM change.

Kolton5543

How long ago was the swap? As I said earlier, the MAF could be dirty. Its not likely bad. Most fuel injected engines can compensate for fuel changes too quick to hear a change in the idle. When looking for a vacuum leak you wan't to watch the short term trims while doing it. when you hit the leak they will drop significantly. Usually 10%-15%. My experience with propane has never been good. tried it six or seven times and has never worked for me. I've even put it straight into the intake and couldn't see a change in the trims. I usually use brake clean. Works every time.

mbomberz1

The swap was almost exactly 2 years ago now. I will try to give the MAF a cleaning to see what happens, only reason I dont think it will help much is because Iv noticed this trim situation since the I completed the swap. Still worth a shot though!

In other news, I was watching the trims again while at different RPMs sitting in neutral not moving. It actually does seem to be dropping down with incread RPM which should indicate a vacuum leak from what I understand. The higher the RPM/load , the less vacuum created, the less air getting sucked in the leak = better fuel trim.

I am going to give your brake cleaner trick a try soon and report back. Thanks Kolton