Plenum pull and injectors in my near future...

[ram_g]

So I've posted elsewhere about taking back my new Nittos to Discount Tire and replacing them with a set of Michelins. The newfound ride smoothness has highlighted a bit of roughness elsewhere - specifically a bit of vibration on hard acceleration, felt primarily in the shifter but also pretty much everywhere. The Nittos masked that so I hadn't really paid it much attention these last few months.

I've been mulling over this vibration the last few days until I made a chance discovery last night. I normally drive everywhere with the power key turned on, but last night I forgot to turn it on and immediately noticed that there was no vibration on acceleration. Turned the power key on and turned on the vibration as well.

Today I did several back to back runs and confirmed the finding. The secondaries are definitely working as there is definitely increased power at the higher RPMs, but the vibration is absolutely correlated to the secondaries coming on.

Back at home I did a couple of Haibeck's tests - checked the amp draw of the fuel pumps (~10 amps, good) and grounded pin 17 of the green ECM connector (yes, both secondary actuators move). And there are no error codes.

So all this leaves me with the injectors and hence a forthcoming first plenum pull. I have Haibeck's DVD and have just placed a substantial order at Jerry's.

(My car is a 1991 that I purchased 4.5 months back with 12,850 miles on the clock. It now has almost a 1000 more, and that is despite pandemic-induced inactivity! The car sat for many years before I bought it but is generally in very good shape and almost completely original. I have been using non-ethanol gas thinking the injectors would be fine, but alas it looks like that is not going to be the case...)

If anybody thinks I am NOT on the right path, please let me know!! (And wish me well for the plenum coming-of-age-ceremony!)

[Paul Workman]

Mixed bag.... I think I got it straight: You mentioned swapping the NITTOS & injectors - both relative to vibration? Sounds like fuel issue - injectors come to mind, and that slight miss too reminds me of similar symptoms that turned out to be a combination of non-tolerant (alcohol) injectors, AND need of a new fuel filter, perhaps culminating into a burnt exhaust valve!

The Plenum Pull is a "Rite of Passage" into the Brotherhood of the Beast! Congratz! Let us know how it is resolved (knowledge is golden!).

Paul

[ram_g]

You mentioned swapping the NITTOS & injectors - both relative to vibration?


Yeah, I made a couple of comments in this thread, specifically posts #14 and #19 > https://www.zr1.net/forum/showthread.php?t=32206

Basically as soon as I got the car I had put on the Nitto NT555 G2s which had a substantial vibration at speed. That vibration masked anything else. As soon as I installed the Michelins the ride became a lot smoother and that allowed me to pick up the remaining vibration that is clearly related to the secondaries actuation.

AND need of a new fuel filter,

Good point on the fuel filter, I have not replaced that yet. Will add to the list.

[ZR2]

I had a 91 and now have a 94. I pulled the plenum on the 91 as the secondary injectors did not work. It was my first plenum pull. I used at the time the Fuel Injector Connection (FIC) injectors. What a quality piece and it changed the life of the car. I recently hjad a coil go bad on my 94, so off with the plenum and basically replaced again all the injectors with FIC injectors and all new GM coils and also new GM replacement wires and plugs. New Jerrys Gaskets etc. It has been going on for awhile and I finally got tired of looking at it in my garage.....Bad Mark........and just finished 2 nights ago. All went good. As long as you take your time no issues.

[Paul Workman]

I had a 91 and now have a 94. I pulled the plenum on the 91 as the secondary injectors did not work. It was my first plenum pull. I used at the time the Fuel Injector Connection (FIC) injectors. What a quality piece and it changed the life of the car. I recently hjad a coil go bad on my 94, so off with the plenum and basically replaced again all the injectors with FIC injectors and all new GM coils and also new GM replacement wires and plugs. New Jerrys Gaskets etc. It has been going on for awhile and I finally got tired of looking at it in my garage.....Bad Mark........and just finished 2 nights ago. All went good. As long as you take your time no issues.

Why did you replace the injectors AGAIN? :icon_scra If they were stainless steel (alcohol tolerant) I wouldn't think you would ever need to replace them again - at least not until after considerable time/miles, etc.

Course if you opted for the so-called "rebuilt" (i.e., non alcohol tolerant) injectors the first time, THAT would answer the question as to why you had to replace them AGAIN....

[ram_g]

Why did you replace the injectors AGAIN?

The way I read his post, he replaced the injectors once in his '91 and then once in his '94. The "again" in his post seems to reference the use of FIC injectors once more.

[ZR2]

Correct....two different cars. Just seemed like a prudent thing to do on the 94 since a coil was bad. No evidence that the original injectors had an issue but thought......while I was in there. I have an injector cleaner and might throw the ones I pulled out on it just to see exactly how they spray etc. More curiosity than anything else.

[ram_g]

As the subtitle says, I've now R&R'd the plenum and the injectors. It's been raining nonstop so I haven't had the opportunity to test the new injectors, but basis the resistance values of the old ones, I think I will see a significant improvement.

First, some very general observations:
1) Marc Haibeck's plenum DVD is an absolute must and is worth its weight in gold. I transferred the DVD content to my ipad and had it as a reference the whole time. As well, historic posts on this forum were very valuable.
2) I'm not sure I've seen this mentioned anywhere else, but someone attempting this for the first time needs to be aware of their own physical limitations for the job. Plenum removal and subsequent work in the engine valley are not technically hard to do, but do involve a lot of bending and reaching over the tires. I am not proud to say this, but physically I am short and fat - clinically obese, to be honest. That makes it impossible for me to perch on the radiator or on the plenum itself as Marc does in his DVD, and bending over the tires for a significant duration put a strain on my lower back like I haven't felt in a while.

From a technical point of view, my two main difficulties were
a) R&R of the DIS connector in the back of the plenum. I simply could not reach down the back of the plenum with it in place, as Marc does. I had to move the plenum forward and cant it a bit to one side, to allow access for uninstallation and reinstallation. In the process of putting it back on, I dropped my long 1/4" socket into the valley and have not yet found it (separate thread on the topic).
b) R&R of the primary injector lower seals in the injector housings. Marc's DVD does not cover this. I had to resort to stabbing these with a pick to get them out, and came perilously close to dropping/pushing both old ones and new ones (in the process of installation) down the injector holes. Fortunately I was able to fish all of them out and everything worked out, but there were a few tense moments. Only afterwards did I realize that Jerry's website has instructions for this operation, including the pure genius step of using a tethered cotton ball to prevent any of these seals dropping into the hole. I found this too late for my work, but others should take note and download the instructions from Jerry's site.

One last observation, along the lines of technical difficulties. I bought and installed FIC injectors from Jerry's site - these were great, with the primary and secondary injectors separately bagged, with the primary ones already having the offset tab on the connector ground off, and only the secondary ones having the lower o-ring seals on the injectors themselves. Great, except that the injector bags were incorrectly labeled with "primary" and "secondary" interchanged! In researching this issue, I further found that MANY references in this forum are also incorrect - e.g. many references to the secondary injector connectors having the offset tab that must be ground flush. Both Marc's and Jerry's sites are correct and consistent - it is PRIMARY injectors that have the offending offset tabs, and the same PRIMARY injectors in the early cars that have the larger lower seal located in the injector housing, but as stated, the labeling of the FIC injectors was incorrect and many references in this forum are similarly incorrect. Not a very big deal because all you need to do is match like for like when R&R'ing them from the injector rail, but quite confusing if this is your first time and you're trying to follow all the instructions precisely "to the T".

[ram_g]

Having removed all the old injectors, that per the part numbers looked to be the originals that came with the car, it was easy to measure resistance values.

6 of the 8 primary injectors came in between 12 and 12.4 ohms, cold.
2 came in at 6.1 and 6.3 ohms, which per Marc's article on the subject, is well on the way to failure.
It's interesting that I didn't really detect any issues with the car running on the primary injectors.

7 of the 8 secondary injectors came in similarly a bit more than 12 ohms.
1 came in at 0.9! Yes, almost fully shorted.
I think when the secondaries were activated, the car was running on 7 of them only. And that's probably the cause of the vibration I was feeling.

My car only had 12.8K miles when I bought it and now has 13.7K miles. Apparently you don't need to have high mileage for the early cars to suffer injector failure.

I forgot to measure the resistance values of the new FIC injectors before buttoning everything up, so I'm assuming they're all good. I haven't yet had the chance to take the car out for a drive with these new injectors.

As a side benefit, I'm looking forward to not having to plan ahead to source ethanol free gas (available ~30 miles away from me) and being able to pull in to any old gas station.

[XfireZ51]

I measure resistance as Marc suggests, ie after about a 30 min heat soak. The FICs in my motor measure at ~ 16.5ohms that way.