Correct injectors?

[Paul Workman]

A little more information...

Hib mainly is referring to static fuel pressure test conditions.

Under dynamic (under load) testing without the secondaries being signaled ON, as you saw the pressure was around 46 psi, which is GOOD.

The secondary fuel pump is switched ON by the ECM when rpm AND throttle position parameters are met. At that time, dynamic fuel pressure should jump to approx a steady 52 PSI. (This test assures the delivery to the fuel rails under load is good.)

Even if the FULL POWER switch is always on, (mine it too, by the way) the secondary fuel pump is NOT turned on until BOTH the RPM and minimum THROTTLE POSITION requirements are satisfied. (Testing the dynamic fuel pressure is what my photo was attempting to show).

Note: At this point I'm almost sure we can dismiss the fuel delivery to the rails, at least, as probably OK...for now.

With regard to injectors, they must be alcohol resistant if ethanol is mixed with the fuel. (Mine were initially replaced with standard, non-alcohol resistant injectors, but they began to go bad after only a couple years of exposure to ethanol.)

The Summit Racing part number for the 21# Accel part no. ACC- 150821 (for 8, but 16 required for the LT5. Note that Summit part number ACC-150121 is for a single injector purchase.) or FIC sells the Delphi injector sets, complete with injector housing gaskets. Recommended new upper O-rings for the primary (1990) injector housing. But, regardless of which injectors are used, refer to the manufacture's recommended voltage off-sets for best results.

Note: Injector resistance must be checked when the engine is at or near operating temperature. They should all read (compare) within range of 1.5 Ω, average between 12 and 14.4 or so, depending on manufacturer. A reading about 3Ω+ lower is suspect; 4+Ω lower than the average is trouble!

Throttle Position Switch: Switch on, engine not running, refer to the schematics, but the signal voltage should range smoothly from idle to WOT. If it is erratic, that WILL cause issues!

Other items include ignition issues. Each of the 4 coils fire two plugs at the same time. If one cylinder is miss-firing, chances are the mating cylinder is missing some as well.

Like to spend more time on this, but leave for now. Good luck. Let us know your progress.

[XfireZ51]

Agree w Hib that the description of the issue is really not clear. Can Jaap describe exactly what's happening and when? Scan data would also be very helpful.

[Jaap]

Originally Posted by XfireZ51

Agree w Hib that the description of the issue is really not clear. Can Jaap describe exactly what's happening and when? Scan data would also be very helpful.

Well let`s give it a try.
First of all my apology for my poor englisch, it`s complicated to explane from dutch to Englisch..

First an update of the work we have done so far.
The injectors have been replaced with FIC injectors.. after that the engine ran mutch better, but not as it should be because of misfire.

The previous owner changed with the engine rebuild 2 ingnition coils so we decided that we should change all 4 of them and the sparkplug wires. After that the engine ran pretty good but only above 4000 rpm.
Under 400 rpm it felt like misfire

Today i pulled the plugs and cilinder 2,4 and 6 where very bad, i didn`t had the right tools to pull plug 8 (that i do tomorow) the plugs show a nice light brown color that indicates that the injectors work well. despite the right color it shows some sort of welding pits in the electrode. The sparkplugs will be changed for new plugs

But.... to make it more complicated there is another issue and that is:
The exhaust mufflers where removed by the prevous owner for more sound.. as it turns out the mufflers are for a LT1 or L98 engine and they where welded on the exhaust, so there is a hughes restriction in the exhaust. Probably the catalatic converter is damaged because of the resriction.

Thats how far we are right now, what i`m planning to do is cut open the catalyc convertor and remove the material inside of it. and of course change the sparkplugs.

I hope i explaned it well and understandable.

All help and advise is welcome

Gr Jaap

[XfireZ51]

No apologies necessary. Your English is fine. Can u give more detail on the misfire. Doubt it's the mufflers.

[Franke]

Also, when you pull the plugs can you get a compression test done on all 8 cylinders just to make sure they are balanced?

[Jaap]

We have done a compression test. the compresssion for
Cil 1#220 psi
Cil 2#235 psi
Cil 3#220 psi
Cil 4#230 psi
Cil 5#210 Psi
Cil 6#230 Psi
Cil 7#215 Psi
Cil 8#195 Psi

[Franke]

Jaap, I would check that cylinder #8 again. I believe that the difference between the highest reading cylinder reading (235) and lowest cylinder reading (195) cannot be more than 15% to have a good balance. Based on these numbers #8 is at approximately 17%. I would do a wet cylinder test to verify.

[XfireZ51]

Originally Posted by Franke

Jaap, I would check that cylinder #8 again. I believe that the difference between the highest reading cylinder reading (235) and lowest cylinder reading (195) cannot be more than 15% to have a good balance. Based on these numbers #8 is at approximately 17%. I would do a wet cylinder test to verify.

Agree. #8 looks suspect.

[mike100]

My lowest cylinder was more like 205 and the rest were 210 on my gauge (and not cranking it forever to get a peak number). It still sounds like maybe one of the newer injectors went bad because it it runs ok over 4000 rpm, maybe the secondary injector is providing good fueling enough to feel ok on power and smoothness.

I guess there is a small chance the injector driver or wiring to that injector is bad- maybe scope the injector signals or check for a broken wire right at the injector connector. It might be hanging by two or three wire strands with an intermittent contact.

[Jaap]

Hi,

I just don`t understand why and how but the probem is solved and i`m very happy about it.

This aftenoon i changed the new ac spark plugs for the old Bosch super plus sparkplugs. And the LT5 ran inmediately very well and smooth.

When my son and i took it for a test drive it scared us both how fast the zr1 rides. Great fun.

thx for all the help.

Gr Jaap