Plenum Pull...Parts List Varification...

[A26B]

What about the valet key? Isn't there so e history withthe early valey key switch not making contact?

Nothing he is telling us regarding symptoms, really points to a miss. vacuum system is good, no codes, no noticeable miss, just no secondary power difference. soinds like the valet key to me.

[| 1990 ZR-1 |]

Originally Posted by tomtom72

I did some checking in the FSM. I think I'm correct in thinking the the 2* injector relays are okay as you did get ohm readings. Also, the 2* MAP is okay as you didn't indicate any SES light, either steady or flickering and you didn't mention that the car stops at 3,000 rpms, that's a DTC 61. No DTC 61 eliminates the secondary vacuum system in it's entirety the way I read the diagnostic chart. I could be wrong on that though.

Therefore, I think a look see at the spark plugs is in order to see the mixture condition. Also, the fuel pump test is also a useful diagnostic tool at this point, the KOEO test. You could have some one rev the car and go stand & smell the exhaust to see if it's lean, but then you still would need the fuel pump test. Unless the 2* injector tips a blocked solid with crud I can't see what's wrong if the fuel pumps pass the test.


Tom

Tom thanks for the thorough repose. Here are some answers to your questions. The SES light is not eliminated at all while the car is idling or under load, and I know it?s functional because it comes on when key is on. I had to unplug the connectors from the secondary injector relays in order to get the resistance reading, so I can?t really tell if the relays are functional. The FEP light comes on with the valet key and stays on. It does not flicker at all even when I jiggle the key.
This morning I started her up, and right away I noticed she was idling rough. The engine was vibrating more than normal, and there was also a strange clicking sounds coming from the right side of the engine and a knocking sounds from under the engine. I?m assuming this is due to the misfire. I took her out for a spin, and she definitely did not run normal. Felt like a misfire. A lot of vibration was coming through the steering wheel. The vacuum seems to be okay. I also pulled all the plugs, and they seemed fine. I replaced them and the fuel filter today. I also bought a fuel pressure gauge, and the pressure while idling read 43 psi and about 50psi at WOT. Is this within the norm? I went through the whole car with a fine comb thinking maybe I knocked out a connector, or a wire, or a vacuum hose, but everything seems to be where it belongs. Now she ran fine in the normal mode prior to this, and the only thing that I?ve done to her since the last time I drove it was measure the resistance of the primary and secondary injectors, and the check the secondary actuators by shorting pin c17. I?m puzzled as to why this would cause a misfire unless it?s a coincidence and one of the injectors went bad. I did, however, measure the resistance of the primary injectors again, and they all read between 13.6 to 13.8 ohms which is within the norm. Any thoughts?

[mike100]

My injectors ran worse with heat soak, but 4 of them read low ohms (one was even 6 ohms). It's almost a given that your injectors are suspect if they are indeed originals- I'd plan on doing that anyhow.

the knock is the dual mass flywheel having fits. it will go away when you find the problem.

[tomtom72]

Okay now we're getting some where! Very good reporting of symptoms so now we have something to kick around. Mike has it in a short version.

Now here is the long winded version.

The strange "clicking" from the right side is/are the 1* injectors firing but no gas is coming out. The gas cushions the sound of the mechanical bits. Therefore my guess is right side 1* are not allowing gas in from the fuel rail, ......or every spark plug on that side of the motor is cracked and arching against the head which I doubt.

Second, the clanking from "under" the motor is the Dual Mass flywheel reacting to the uneven power pulses and it makes that noise as it reacts to miss-fires or dead cylinders.

My humble conclusion is the OEM injectors are on there way to injector heaven. However, two more tests .... sorry, but this is what I would do as I'm new to computer cars & EFI! Pull the plugs and compare left to right bank. The ones not getting fuel will look cleaner than the ones getting fuel. Idle the car and go stand behind at the exhaust pipes and get a good nose full of the exhaust. Does it burn your nose and eyes? If yes that is a lean condition you smell, which points back to the 1* injectors not passing fuel. The exhaust smoke should be a fairly white vapor from the leanest side and the richer side will be darker & smell rich.

If at this point you have a scanner & plug in you will see that the fuel #'s are nuts as the ECM tries to add more fuel in response to the O2 sensors' feedback info. The scan at first looks like the motor is rich, but it's not because the scanner only sees the ECM's reaction to the O2 feedback, lean, and tries to add fuel. Anyway, if there are some primaries that don't work, the secondaries can't make up for it when they come on line. Hence the poor mid range and top end performance. The vibration thing is my tell tale as it's looking like a lean miss from where I sit. If I was there I'd do my smell test and use my scanner.

Next, I'm not all that happy with the fuel system's PSI readings, but with 21 year old pumps what do you expect. I would consider doing r&r on the pumps & socks later. The readings are on the low side of the FSM range. Oh, if you don't have one yet, please do look to buy a FSM at Heliminc.com....the best tool you can have in the box!


Tom

[| 1990 ZR-1 |]

Originally Posted by tomtom72

Okay now we're getting some where! Very good reporting of symptoms so now we have something to kick around. Mike has it in a short version.

Now here is the long winded version.

The strange "clicking" from the right side is/are the 1* injectors firing but no gas is coming out. The gas cushions the sound of the mechanical bits. Therefore my guess is right side 1* are not allowing gas in from the fuel rail, ......or every spark plug on that side of the motor is cracked and arching against the head which I doubt.

Second, the clanking from "under" the motor is the Dual Mass flywheel reacting to the uneven power pulses and it makes that noise as it reacts to miss-fires or dead cylinders.

My humble conclusion is the OEM injectors are on there way to injector heaven. However, two more tests .... sorry, but this is what I would do as I'm new to computer cars & EFI! Pull the plugs and compare left to right bank. The ones not getting fuel will look cleaner than the ones getting fuel. Idle the car and go stand behind at the exhaust pipes and get a good nose full of the exhaust. Does it burn your nose and eyes? If yes that is a lean condition you smell, which points back to the 1* injectors not passing fuel. The exhaust smoke should be a fairly white vapor from the leanest side and the richer side will be darker & smell rich.

If at this point you have a scanner & plug in you will see that the fuel #'s are nuts as the ECM tries to add more fuel in response to the O2 sensors' feedback info. The scan at first looks like the motor is rich, but it's not because the scanner only sees the ECM's reaction to the O2 feedback, lean, and tries to add fuel. Anyway, if there are some primaries that don't work, the secondaries can't make up for it when they come on line. Hence the poor mid range and top end performance. The vibration thing is my tell tale as it's looking like a lean miss from where I sit. If I was there I'd do my smell test and use my scanner.

Next, I'm not all that happy with the fuel system's PSI readings, but with 21 year old pumps what do you expect. I would consider doing r&r on the pumps & socks later. The readings are on the low side of the FSM range. Oh, if you don't have one yet, please do look to buy a FSM at Heliminc.com....the best tool you can have in the box!


Tom

Hi Tom, I had a chance to run out to the garage and do some of the tests you specified. The plugs are definitely not cracked. I installed new ones yesterday. I did smell the exhaust and definitely burned my eyes coming out of the right side. Also, the first thing I bought for my Z was the FSMJ. I?m still learning to navigate through it. I?m very handy, but is not a mechanic of any sort. The FSM has definitely been very helpful in troubleshooting, and it?s a very interesting read in general that helps me understand the inner workings of this car.
I also performed the old trick of placing the tip of a long flathead screw driver on top of the injector connector and placing your ear on the tip of the screw driver handle to listen to the injector ticking away and confirming normal operation. Sure enough Injector #6 was not ticking at all, while all the rest ticked away like clockwork. So I pulled the #6 spark plug, and sure enough it was brand new when compared to plug #4 next to it which looked normal.
I also hooked the fuel pressure gauge up again, and noticed when I turned the key on, the fuel pumps kick in and the pressure goes up to about 53PSI for about 2 seconds while the pumps are on (which is within the normal 48-55psi range per FSM), but then immediately starts to slowly drop to zero within 5 seconds and stays there. Per FSM, when key is on, the fuel pumps charge the system to 48-55psi within the first two seconds, and the pressure should stay steady within that range after the pumps shut off and while the key is on. My only conclusion is that #6 injector is stuck open and is allowing the pressure to escape. Please correct me if I?m wrong. Would this also be the cause of the fuel pressure reading slightly lower than normal at 43psi while idling? Maybe the fuel pressure regulator is unable to keep up with that faulty injector? I?m just speculating at this point.
I was able to see part # on the primary Injector # 2, and it read 5235357. I googled this part # and it?s coming up as a GM OE injector manufactured by Rochester which I believe are the original Multec injectors.
Tom, I think new injectors are in order, but before I do that, I wanted to see if there is anything else I should check. I?m just still worried if my checking the injector resistance the other day caused the failure, or if it was a plain coincidence. Let me know what you think.

[mike100]

101% of these pre-93 GM injectors are bad so I wouldn't spend too much more time except to figure out how much money they are going to cost you.

Just in case you haven't found this- I think these will be the cheapest NEW injector set for the LT5.Click Me

I think there is a rebuilt option for $350 as well. The car is going to run so much smoother afterwords, trust me.

One other fundamental diagnostic that might give you piece of mind would be to disable the igntion/fuel inj by removing a fuse and run a compression test. Should be 200 psi or so after 3 cranks.

[mike100]

The only other bit that came to mind is that the car will run really badly for a few seconds after the new injectors go in. It will be injecting air until the fuel rails flow through the injecotrs and the dual mass flywheel will REALLY make some noise for 4-5 seconds- don't be alarmed- just expect it to be rough during the high idle flare up when the car starts.

[tomtom72]

Your Z and mine must be related as my right bank injectors went out also! It those damn right wing guys that cause all the trouble!!

Yea Gary it's the injectors so that's that! The fuel pressure is another issue.

I had much the same reading on my OEM pumps at about 16 yrs old or so. I think that they get tired is all. I bought new pumps and put them in and viola back up to factory specs. You don't have to do that right away. I waited at least two yrs before I replaced them and the only ill effects was I was missing some acceleration quickness old vs new pumps. Fuel delivery is key because we move so much air when the secondaries kick in! It was a nice dividend.

Oh, #6 injector is not causing the drop in FP, rather it proly is a couple of leakers somewhere. Proly from the secondary injectors as they are prone to get gummed up and leak a tiny bit. All you need is a few to loose FP rapidly upon shut down. It also could be the pump impellers as they wear from cavitation they don't fit tightly any longer and you leak back into the tank thru the feed line. The regulator is A-Okay as long as the hose doesn't have fuel in it.

Good deal, now go get you some new injectors and have some fun learning the first course...Plenum Pulling 101!

[| 1990 ZR-1 |]

Mike and Tom,

Thanks for your help guys. I'm going to order the injectors and gaskets, and hopefully be done with these issues by this weekend. (Wishfull thinking). I'll post up the results.

[mike100]

Originally Posted by | 1990 ZR-1 |

Mike and Tom,

Thanks for your help guys. I'm going to order the injectors and gaskets, and hopefully be done with these issues by this weekend. (Wishfull thinking). I'll post up the results.

Then don't do what I did and decide to port the injector housings while you were in there or you'll really get behind schedule. You could have it done in a day taking your time to see how it comes apart.