Hey guys, working on a RB25DET at the moment, stock Internals, OP6 turbo, forward facing manifold and supposedly 850cc side feed injectors with a Haltech Sport 2000

Ok so fuel pressure is good, and setup all the parameters in the haltech to suit 850cc injectors... Normally I like around 50-60% in the VE table around idle... I found I had to add a +30% overall fuel trim as well as have figures in the 80's to get it to idle at 13:1 which didnt seem right so I reduced the injector size down to 550cc and much better with 0% overall trim and 55% ve at idle.. This tells me that the 2nd hand injectors the customer got which he was told are 850cc are actually closer to 550cc? I guess ill have a better idea once Ive done some more tuning and get a look at the duty cycle.

But main problem is it wont idle nicely without missing unless I richen it up to richer then 13.0:1 with it liking it best around 12.5:1 now on other RB's I can usually get them idling sweet around stoic... as soon as I try to go leaner then 13:1 its very erratic and AFR's swing back and forth between 13 and 16:1 and can hear the engine missing... Would this be due to the oversizes old tech side feed injectors? The ecu is asking for 1.5 - 1.6ms pulse width so im thinking im just operating outside the injectors linear range?

I thought maybe the o2 is getting a wrong reading, ive got the Haltech WB02 in the dump pipe and the dyno sniffer up the tail and they are both reading withing 0.2 of each other... had a good listen for any exhaust leaks and could not find anything... One thing to note that im not sure if it means anything, I threw some brand new clean plugs in there, let it idle at 12.0:1 for a lil while then pulled a plug... it looked to be 100% brand new... I was expecting it to be a little sooty if it was indeed idling that rich? or will it not really soot up until you get to sub 12's?

So yeh what do you think is more likely?

sounds like you're just around the injectors dead time when you want to lean it out at idle.

what about cam timing? maybe timing is off and overlap is off.

Are they purple topped DW injectors?

If they are an unknown I'd get them tested or rig up your on test bench to check flow and spray pattern

Ok so seems I was wrong about the injector size, half tuned so far but making 300rwhp and only 38% duty cycle. If they were 550's I'd expect them to be around 60%ish at that point... My fuel map has ended up being very flat as well with low load/rpm numbers being low 50's and 14psi boost areas are only just over 60's

With Regard to Cam timing Tommy... I did change the timing belt on this motor, was pretty certain I had it right but ya never know. But I thought if one of the gears was a tooth out it would run horribly? It idles quote nice once it has consistent fuel supply...

Since these injectors are bigger then I thought, old school style and asking such low pw at idle I'm pretty sure it's just below their linear range.

I've had similar issues with DW side feed injectors in an S15 a while back and I came to the conclusion that they may not offer the best linearity

at very short pulse widths. In my case the initial dead time values we had were incorrect and extending the dead time actually improved the idle considerably. I believe what was happening was that the combined incorrect dead time value plus the commanded pulse width at idle was probably on the verge of the injector simply not opening at all.

I had a very similar situation to what your describing Andre, injectors that were meant to be 550cc behaved better when I ignored the dead times on the DW website and worked out my own

Well the hi-flowed OP6 turbo made it to 300rwhp then the bearings decided they didn't want to hold the shaft in place anymore :S

Had the original stock turbo still so stuck that on, decided the throw the stock injectors back in too... Idles beautifully at 14.7:1

The engine also had a random misfire while tuning in steady state that I couldn't figure out... After I changed injectors it didn't misfire at all!

What would that be then exactly? One or more of the injectors not firing consistently or maybe one flowing a lot less/more all the time?

I would pin it on injector flow until they were tested. If your testing company has the capability I would see if they would get the lag times for you too

My experience with these injectors in two applications plus what I've heard from others doesn't shine a good light on the DW side feed injectors unfortunately. I recall we had a set that we fitted to an s15 that we ended up pulling out and returning as we couldn't achieve a decent idle quality.

Sadly your choices in the side feed figment are rather limited.