87 930 Hesitation - Fuel injector replacement

[SG930]

Recently running new SC cams in my 87 930. It has been running very good and strong but recently experiencing varying hesitation and stumbling under 2000 RPM. Verified fuel pressure, wur cold and warm pressures and adjusted AFR to idle at 12.5 ish. All number are within spec and per the wur build sheet. With the idle AFR at 12.5 I got cruising AFR at 14.2. My AFR numbers flicker all the time currently vs being a constant, like a constant at idle or at a constant cruising RPM. Idle would be 12.5 to 13, not a consistent number.

I have done quite a bit over the 2 years I have had the car. It had an upper rebuild including new rings. Rebuilt FD, BL wur, RPM switch. I recently did new SC cams, rebuilt turbo ,new RarlyL8 headers/muffler (awesome!). Did new plugs, cap and rotor with SC cams. The first year I did the CDI, ignition coil, fuel accumulator and filter, fuel lines including CIS lines.

My next item was going to be the injectors. Would the flickering AFR's be due to inconsistent/different flow/plugged etc fuel injectors?

What is a good replacement injector? Stock? Appreciate the help as there was no way I could have done much of this without the help of this board. Thank you.

[908/930]

I am curious what others will say with fluctuating AFR. Mine fluctuate up and down like you are saying. It appears to get slightly better after a longer run I was thinking the O2 sensor temp gets more stable, mine is positioned further away from the turbo. I also replaced the injectors last year and balanced out the fuel flow to them, car runs well as is so not that worried about the AFR changes.

[gsxrken]

New stock injectors will likely be an improvement. The original ones are nearly 40 years old. My car ran great after a rebuild a new injectors, but I’ve never seen a rock steady AFR either. It flickers a bit. But a stumble is not typical. You might want to check for loose or cracked injector blocks. That’s also common.
Ive also noticed if I cruise in the 14+ range I get just too much popping on decel. With the 10% piss gas, true lambda is more like 14 or so rather than 14.7 for ethanol free gasoline of old.

[908/930]

Does your ignition distributor advance/ret work properly?

[SG930]

I had a previous post with my ignition timing that I was working on. I am maxed in the slot and was at 20 degrees at 4000. I never did the adjustment. I will revisit this. Thank you.

https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/1166850-1987-930-ignition-timing-question.html

[SG930]

Is it worth the $90 dollar per injector difference to go with the 009 bosch injectors vs the 017 bosch injectors?

[reclino]

CIS fuel volume is controlled by the fuel head, injectors job is to atomize the fuel sent to them. No performance benefit unless you modify the fuel head,.and put on the larger diameter fuel lines...

[SG930]

I do have a modified fuel head but not sure about the lines. Anyone know if there are larger available fuel lines and what there size would be compared to stock USA fuel lines?

[Tonger]

I measured the difference - the Euro lines are much bigger than the US lines. There is much less resistance to flow with the Euro lines - calculation is in the final post of the thread linked below.

Outer diameter: 6 mm Euro, 4 mm US
Inner diameter: 2.75 mm Euro, 2 mm US

This thread has 009 fuel injector and euro fuel lines discussion.

https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/863588-cis-hp-hard-ceiling-cis-injector-flow-rates.html

[SG930]

So you are saying that there's no improvement with a modified fuel head unless you change to the euro lines and 009 injectors? There seems to be a lot of modified fuel heads out there but I guess I was not aware of the option of the larger euro fuel lines and even their availability. In that case, even though I have the modified fuel head and do have the usa 4mm lines, it would make sense to go with the cheaper 017 injectors saving big $$.

[908/930]

SG are you running stock turbo/intercooler?

[SG930]

No. I wish I knew how to list my stuff in the footnote of my posts. I have a fabspeed intercooler with a fresh K27/K29 hybrid turbo, new rarlyl8 headers and street muffler.

[908/930]

SG, if you go to user CP/settings & options / edit signature you can add info there. How were your AFR at redline with your existing injectors? With the add ons you have I would want the euro injectors.

[SG930]

I do have and RPM switch too. I do believe 11.5 ish.

[SG930]

Welp. I screwed up #1 and #2 injector lines. #1 was already twisted and I had a 13mm instead of a 12 on the injector while removing the line nut. Anybody know where i can source euro lines? Braided alternatives?

[Alan L]

I would be considering an airleak with low rpm stumble - if all other options are covered - ign etc.
If it is easier to replace your lines with stock, and cost wise, I would stick with them.
I switched to Euro lines (was running short of fuel at high rpm). I did a back to back test as I switched them out - to see what increased flow I got by going to the bigger lines (all else unchanged). My total flow increased by 1-2%. So the lines were not the limiting factor.
Unless you have a highly modified FD and are looking for big numbers, I think the stock lines will be sufficient. If you can easily and no real extra cost, source the euro lines, then nothing lost in fitting them. But no real gain in this situation either.
The biggest change to increasing my flow rate was ditching the fine screen on the inlet to the FD. I suspect not every FD has one - but that is definitely a flow restrictor.
Alan

[SG930]

I did notice a fold in one of the fabspeed neoprene(?) collars from the throttle body to the intercooler. Most likely it but I messed up 2 fuel injector lines that look hard to source. I'll call our sponsor tomorrow. Thank you for the input.

[Alan L]

If you put a WTB on the F/S site you can probably source a set (surplus to EFI conversion). Alternatively, by salvaging the end fittings a hydraulic shop that makes brakelines, fuel fittings etc can probably manufacture replacements.
Alan

[SG930]

I replaced the injectors with euro size. Since I had buggered up a fuel line a had some brief time to replace the spark plug wires which I have meant to do but was putting it off. I got replacement lines from Einmalig and installed those last night. The car runs awesome now. No hesitation at low rpms, much smoother warm up and reduced "pops" on decel. It was a tough start with the new empty lines though. Wish I would have done the wires and injectors separately to see the results individually. Very pleased with the maintenance items and the results of the SC cam swap. Now I just have the pesky leak I believe to be the pulley side crankshaft seal (which I replaced). Thanks all for the help!

[gsxrken]

Glad to hear you’re happy with it. Curious to hear if your AFRs held steady from your first post or if you needed tweaks. Less popping sounds richer to me.