GTA1990

iTrader: (1)

Help really needed for a car I'm hoping to take to a road-trip. I latched on to someone else's post about engine vibrations and got some useful feedback about it possibly being engine mounts, harmonic balancer which i've got the car booked in for but in a couple of weeks

Anyway, now I come armed with a video showing a live scan tool plugged in.

Link to video:http://jmp.sh/hKfhkZO

Symptoms
Uneven idle and can't really hold a steady rpm (fluctuates slightly per the video). engine vibrations (throughout rev range and both with the car in neutral and in gear) and stutter from take off (more pronounced when cold)

Things done so far
Plugs
leads
cap
rotor arm
fuel filter
vacuum leaks checked and checked. Header bolt tightened
checked fuel pressure; 42psi on startup and holds slightly higher with the vacuum line to FPR unplugged and on idle and when given some gas. Bleeds down after a few minutes though

The uneven idle makes me think it may be a mechanical issue but notice the short term fuel trim and long term indicating a lean condition. Really welcome any input on this

anymore info you need let me know.

Car is a 91 LB9 T5. Stock apart from the hedman headers and exhaust

Tuned Performance

iTrader: (92)

If the injectors are stock multecs they are problematic. The coils short.
You might want to contact Southbayfuelinjectors injectors for a set of 19#hr injectors.
https://www.southbayfuelinjectors.co...tors-1985-1992

GeneralDisorder

iTrader: (1)

It's adding fuel according to the BLM.

Couple that with the reputation for Multecs to short out, and this would mean less flow and therefore cause the ECM to attempt to compensate with a high BLM to get more fuel from the remaining injectors.... your vibration is one or more cylinders not firing from a poor flowing injector.

Get a set of SouthBay injectors and a plenum gasket set. You need them even if you don't need them.... if that makes any sense.

GD

GTA1990

iTrader: (1)

thanks. I ohm'd them when cold and all were in the 16 range but I appreciate that doesn't necessarily mean they're good.

I found the swinging short term fuel trim interesting. With holding the revs slightly above idle it seems to be adding fuel but then holding the revs ever so slightly higher, it seems to be pulling fuel? Would that be symptomatic of bad injectors?

I'll most probably go ahead and change them as I can't see anything in the history other than the injectors being cleaned over 10 years ago but still your thoughts appreciated

GeneralDisorder

iTrader: (1)

Their resistance is very often normal when cold. They short out and their resistance drops as they heat up.

GTA1990

iTrader: (1)

cool. Got the injectors on order. Fingers crossed they sort this for me

GTA1990

iTrader: (1)

right, injectors installed yesterday. Followed the instructions (injectors into manifold first) and checked for leaks both visually and for good and maintained fuel pressure 40psi).

No vacuum leaks. IAC counts have some headroom at warm idle (20 or so at 550rpm)

Car now runs very lean. BLM's are 159-160 and it surges at idle once warm. Vibrations are still there and it won't hold RPM.

I've done a few searches and I seem to be finding a consensus that Bosch III's run lean and some have improved the situation by increasing the fuel pressure

grateful if anyone can chime in. I'm disappointed to read that these injectors run lean (especially after spending a day putting these injectors in).

GTA1990

iTrader: (1)

so I took the vac line off of the fuel pressure regulator (run a higher PSI) and wouldn't you know it, BLM's came down to high 140s. Still not acceptable but clearly indicates to me that these injectors need more pressure/ tuning to run correctly

As mentioned above, from my reading this is not a unique situation. To anyone reading this, I suggest you check your BLM's after installing bosch D3/ III injectors.

I'm slightly concerned these are being sold as stock replacements

GeneralDisorder

iTrader: (1)

The consensus is that tuning is a good idea but most people have no problem running them as a drop in. You should take a look at other potential causes of the lean condition.

GD

GTA1990

iTrader: (1)

thanks, I'm happy to keep an open mind and take learned input

Fuel pressure looks good and I visually inspected the fuel rail and close proximity fuel system pieces for anything out of place.

Could anything other than the fuel delivery system cause a lean condition?

GeneralDisorder

iTrader: (1)

Have you checked the MAP sensor and coolant temp sensor readings against shop gauges?

What about a compression test to check overall engine condition?

GTA1990

iTrader: (1)

They seem to be reading commensurate with engine temp, engine RPM. I've disconnected things like the coolant temp, MAP, TPS and it hasn't improved the condition.

A compression check is in order. Though, still unsure how this would contribute to the observed lean condition

GeneralDisorder

iTrader: (1)

Fuel pressure should be 43.5 psi, engine off.

Slowly pinch off the return line till the pressure rises and your BLM's come down to around 128 and see how it idles.

What is the condition of the O2 sensor? It may be indicating a false lean condition.

You may need to burn a chip or increase the fuel pressure. In the end though the Bosch D3's are a more reliable long term solution so it's worth the trouble.

GD

GTA1990

iTrader: (1)

thanks. Return line test sounds like a good idea to build up pressure. I have a new o2 sensor that I'll fit aswell (thought the live data shows it switching from lean to rich regularly)

Out for a few weeks so will try these on my return. Also have some chip burning bits on order that should hopefully be waiting for me when I'm back

Pro

Is that scanner not putting a 1 before the 70 on the coolant temp, or is that in Celsius? Why in closed loop and 70 degrees Fahrenheit

GTA1990

iTrader: (1)

celsius; me no understand fahrenheit too good

chip burning stuff has arrived and have had some of the Prom burning crew on thirdgen kindly chime in with some tuning tips. Will try these and report back. I have my reservations that the vibration issues will be sorted but will be happy for now if the fuelling is broadly stoich

GTA1990

iTrader: (1)

just an update that I burned a chip with a lower injector flow rate (17 from 19) and tweaked the PW tables per https://www.thirdgen.org/forums/diy-...ctors-not.html. Shout out to ULTM8Z and RBOB for the guidance.


Got a bit of a shock when I pulled out the ECU and saw it was a remanufactured unit and had the PROM for an Automatic car? I used a bin file for a Speed density MK6 5.0 to base my tune on.


I also changed the oil and o2 sensor.


Idles and takes off much better; the stutter is gone and it no longer dies/ surges when coming to a stop light. Its drivable now I would say


Interestingly, with the scan tool hooked up, the BLM's were still in the 140's, 130's. I then changed the injector flow to 16 and this brought it down to the mid 130's and occasionally dips into the 140's. I think this is acceptable and will put some mileage on this tune with my scan tool hooked up. Slightly mindful about setting the flow rate as low as 16; welcome anyone's thoughts.


The vibration in the rev range hasn't really improved and I suspect this is unrelated to fuelling and mechanical.

ULTM8Z

That's good news... another hash mark in the column for Bosch-III's needing tuning...

The only thing I caution against with using the injector flow rate to tune BLM's is that it affects every other aspect of fueling as well... open loop, PE, AE, etc..

You can do quick and dirty changes like that to get the car running, but I would strongly advise getting a wide band then going back and re-tuning the VE tables properly as well as your PE and open loop. AE is probably not as critical on the TPI's unless you notice a persistent stumble (not like the Minirams which are notoriously sensitive to AE changes).

I agree with you in your earlier post that the fuel injector companies should probably be putting some sort of caution statement that re-tuning the computer may be required when replacing factory injectors with Bosch-III's. Some people may be able to drop them in with no mods (though out of those, not sure how many "ignorance is bliss" cases there are), but clearly there are people who's cars need re-tuning due to poor performance... seems like we're up to around a 1/2 dozen documented cases on this board now...

GTA1990

iTrader: (1)

Thanks ULTM8Z.

Yep, not to sensationalise/ needlessly labour the point, but my car is stock but for an exhaust and, per the checks I performed, the fuel system seems as factory spec.

So unless I (and others) got a dud set of D3 injectors, I don't think it unreasonable to reach that my experience will be the same for others who install these injectors into their stock cars.

Their cars will run very close/ at/ over the limit of extra fuelling the stock computer can add; i.e. lean without tuning