No or low spark #4 and #7 plugs

[DTZ ZR1]

I have a 90 ZR-1 and I was having a problem with my engine running rough and also having SYS flash on my display. I changed the battery because I did have problems with it and that took care of the SYS. At first it seemed to clear the engine problem. Took the car on a 400 mile trip over the 4th, she performed flawlessly. This week she started to idle real rough and felt like a cylinder was miss firing. I changed the easiest thing the plugs, I put AC 41-602s in. I took 1,3,5, & 7 out and replaced them. I started the motor and it still was idling rough. I then took out 2,4,6, & 8, when I took #4 out it was wet. I replaced those four and started the motor. It idled better, but still not what I liked. I then took #4 wire off, idle did not change. Took all the other wires off, I could hear the spark jump and engine idled rougher except for #7, there was no change. I looked at my service manual and found that they are off the same coil pack so I figured that I would replace all four. The question is while I have the plenum off what else should I change or look at? Also is there anything I need to be aware of when removing it? What would be a good coil pack to replace them with? Thanks for the help.

[tomtom72]

Great diagnostics! :thumbsup: Use the stock GM coils, they give the least trouble. D-555 P/N 10472401 ( I think is the P/N) and the part numbers are here in a thread do a search. Remember the intake is wet, so drain the rad!

I hate to say this, but if the injectors are OEM on your 90 then, well, you know about the alcohol & what it does to our OE injectors....not wanting to spend your money for ya...:o

Other than the coils, I would just check all the vacuum lines, the whole 2* vacuum system in fact while I had it opened up...it's just easier. I'd maybe think about the two temp senders in the left I/H, Starter is okay so just maybe do some clean up on the valley floor to make sure the drain hole is free & open, maybe at least check the CCVB cover bolts ( they were finger tight on my 90, man what a mess they made!) and the hoses to the I/H from the box. Have you had the plenum off prior to this, as I maybe telling you stuff you have dunn already...:redface: If this is the first time let us know so we know where you're at with your Z.

:cheers:
Tom

[DTZ ZR1]

Tom, this is the first time I have attempted this. It is not like my 85. Thank you for the info. Let me know if there is anything else I might need to do. One thing I have read somewhere that there sometimes a problem with refilling coolant and airpockets.

DT

[A26B]

I can provide gaskets & seals if you need them. Use link below my signature.

[XfireZ51]

I have a set of stock ignition coils If you're interested.

[flyin ryan]

DT, when filling the coolant just take your time & be patient, fills rather slowly. Doesn't hurt to jack up the RH front (passenger) side a little to keep it higher than the rest of the system too.

[ZR1Vette]

Since you will be in the area covered by the plenum tighten (torque) every bolt you can see and get to. In particular the crank case vent valve cover (19 lb ft), inspect crank case vent hoses and tighten the hose clamps. Good time to make sure the valley under the starter is clean and the drain hole is not clogged (I just poured a bit of isopropyl alcohol into the valley and should drain out under the engine). Also inspect the secondary actuators and lines. When installing the plenum back follow the tightening sequence shown here>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1nutandboltemplatecloseup.jpg

I used painters tape to cover over any openings...do not want to drop something down those holes!
http://i17.photobucket.com/albums/b79/MRBLU/ZR1secondaryvalveactuator.jpg

When you first lift up the plenum you would be seeing this...front green arrow points to vacuum hose (disconnect) and the red arrows point to the front 2 ignition module connectors (disconnect)
http://i17.photobucket.com/albums/b79/MRBLU/ZR1plenumliftedevapconnectannotated.jpg

Here are the 2 rear ignition module electrical connectors (red arrows)>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1Coilpacdetail.jpg

A handy 'tool' is a wooden hatchet handle ($2.50 at Home Depot) to pry up the fuel rail assembly
http://i17.photobucket.com/albums/b79/MRBLU/ZR1fuelliftingtool.jpg

and to pry up to plenum too>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1plenumliftedinfrontwithwoodpc.jpg

Glad to provide more pointers and pics if you need..
Michael

[tomtom72]

DT, as you see you have come to the right address! We Brothers of the Beast will leave no man ( or women, to be P/C ) out in the cold with a broken Z! Okay enough about our character....but it's true!

First, as this is your first plenum pull you will need a few things. Chief among them would be the use of a FSM = Factory Seervice Manual, a T/Q wrench, Torx sockets (T-45 long), a hand vacuum pump, gaskets ( see Jerry's posted link! ), Mike has given you photos, and a bit of skill from wrenching on cars in general.

If you have most of that, then this is actually alot easier than it looks. Trust me as when I had to do this the first time I think I was scared chitless...:sign10:

Plenum pulls require no more skill than what you used when you did your first sbc intake swap, truth! This is different, and there are a lot more parts, but in actuality you are just pulling an intake manifold. At this forum there are Mike's thread, and a coupla of others. I'm going to list some links for you to look over to gain the needed background info. Look'em over and you'll see it is a lot of detail work but nothing a new Z owner need to farm out. However you will need a place to work when you do this for the first time, after you will pull the plenum in less than an hour round trip.
http://www.pnwzr1.com/
http://www.pnwzr1.net/
http://www.bcvettes.org/?http://www.bcvettes.org/howto/zr-1/plenum/
http://www.zr1specialist.com/
http://www.corvetteactioncenter.com/forums/zr-1-general-technical-discussion/14272-1990-1995-zr-1-secondary-port-vacuum-diagnosis.html

You look and then tell us what you need more detail on. You can do this, even by yourself with the coaching that you can get here.

:cheers:
Tom

P.S. if you lived close to me I'd have been knocking on your door already, tool kit & all!:mrgreen:

[ZR1Vette]

As Tom pointed out...some basic tools you will need:
http://i17.photobucket.com/albums/b79/MRBLU/ZR1tooltableviewcopy.jpg

Also recommend getting new gaskets from Jerry (aka A26B) and if you not obtain FIs yet, many of us have selected the Bosch units from Fuel Injector Connection ( http://fuelinjectorconnection.com/shop/ )...just speak to Jon (great guy and tremendous knowledge on FIs.

Just make sure you install the injectors in the fuel rail correctly... should look like this>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1newinjectorsinstalledinfuelrails.jpg

[vettn71]

Just as an FYI, when I pulled my plenum (first time) it took me 4 hours and I discovered:
1. It's necessary to flush the fuel rails. If you don't a bit of trash may find its way into an injector (ask me how I know)
2. The second time I pulled the plenum (to change the injectors) I installed a set of Delphi injectors Jon Banner had set up for me. My car is a NCRS car and appearance is important. Second pull took 45 minutes. I also put in new coil paks, as I found number 4 and 7 not firing at hat point.
3. Third plenum pull took me 30 mionutes to replace a brand new GM coil. The other three were fine. If you put in coils, check the resistance of the primary and secondary windings before you install them. Could have saved me another pull if I had done that.

Pulling the plenum is pretty easy after the first time. Just watch where things go and read all the information recommended on this site.

Good luck

Jim

[DTZ ZR1]

Brothers, thank you for the pics, it does make me feel a lot more confident about doing this. I just do not want to screw it up. This is a great place for info. I will proably be doing this in two or three weeks. Life is busy and it also gives me time to research.

Jerry I will get with you on the gaskets.

Tom I do have the factory service manual, first thing I purchased after I got the Z. Thanks for the website info.

Michael, thank you for the info and pics. I also like the schematic for the bolts.

Jim, thank you for the info on flushing fuel rails and checking the coil packs.


Thanks, DT

[jonszr1]

what should the resistance be on the primary and secondary.? i have never been able to find those figs

[Kb7tif]

I have a 90 ZR-1 and I was having a problem with my engine running rough and also having SYS flash on my display. I changed the battery because I did have problems with it and that took care of the SYS. At first it seemed to clear the engine problem. Took the car on a 400 mile trip over the 4th, she performed flawlessly. This week she started to idle real rough and felt like a cylinder was miss firing. I changed the easiest thing the plugs, I put AC 41-602s in. I took 1,3,5, & 7 out and replaced them. I started the motor and it still was idling rough. I then took out 2,4,6, & 8, when I took #4 out it was wet. I replaced those four and started the motor. It idled better, but still not what I liked. I then took #4 wire off, idle did not change. Took all the other wires off, I could hear the spark jump and engine idled rougher except for #7, there was no change. I looked at my service manual and found that they are off the same coil pack so I figured that I would replace all four. The question is while I have the plenum off what else should I change or look at? Also is there anything I need to be aware of when removing it? What would be a good coil pack to replace them with? Thanks for the help.

You mentioned 1 spark plug was wet, this is pry a fuel injector sticking open, are the injectors stock.

[tomtom72]

You mentioned 1 spark plug was wet, this is pry a fuel injector sticking open, are the injectors stock.

Good catch! DT was 7 wet also? I would think the chances are better than even money it should have been, although Jeff has seen coils have a one tower failure. Again, not trying to spend your cash for ya, but the word is that the OE multi-techs don't react well to cleaning attempts. It's a judgement call on your part about the injectors.....on the early cars 90 & 91(?), the alcohol in the gas will eventually get them.

Oh, DT, You're welcome!:mrgreen:

:thumbsup:

[Jim Nolan]

Check the injector housing bolts. On mine the inside rows on both sides were finger tight.

[Z51JEFF]

Its not necessary to drain the coolant,maybe a gallon at most as long as your not taking off the coolant pipes.Couple tips,one of the biggest mistakes made when putting the plenum back on it pulling one of the hoses off,mainly the cork screw line,ask me how I know.A good trick is to put the line down in the rubber fitting,make sure its seated,wrap a piece of tape around the line as close to the fitting you can get it.The reason for this,as you lower the plenum in place watch the line,if it has come out of the fitting you can tell BEFORE you button up the plenum.Mine pulled out and couldnt tell by looking at it,it was sitting at the top of the fitting,looked like it was still in the fitting.The only reason for the tape is to use as a visual thing,nothing more.Plugging the harness back into the spark jobber on the bottom of the plenum is a pain.Bending the connectors is really easy and getting the bolt started is also a pain.

[Jeffvette]

Couple tips,one of the biggest mistakes made when putting the plenum back on it pulling one of the hoses off,mainly the cork screw line,ask me how I know.

His car does not have that as the EVAP system is in the front of the car.

[DTZ ZR1]

I will be changing out the injectors, I believe that they are stock. It does not look like anyone had the plenum off. The factory plug wires are still on. I figured on changing the packs and wires too and anything else that might be bad.

Jerry's gaskets come in two different thickness, Which would be better?

I am trying to clear my schedule so I can start on it this weekend. I do not think I could wait three weeks to drive her again.

[DTZ ZR1]

I had already changed it and started the car to see if things changed and I did not go back and take 7 out. I know I should have.

DT

[Jeffvette]

I will be changing out the injectors, I believe that they are stock. It does not look like anyone had the plenum off. The factory plug wires are still on. I figured on changing the packs and wires too and anything else that might be bad.

Jerry's gaskets come in two different thickness, Which would be better?

I am trying to clear my schedule so I can start on it this weekend. I do not think I could wait three weeks to drive her again.


I prefer the thicker gaskets. Less likely to tear under future removal.

Give me a shout on the coils and plug wires I stock them.

[secondchance]

I will be changing out the injectors, I believe that they are stock. It does not look like anyone had the plenum off. The factory plug wires are still on. I figured on changing the packs and wires too and anything else that might be bad.

Jerry's gaskets come in two different thickness, Which would be better?

I am trying to clear my schedule so I can start on it this weekend. I do not think I could wait three weeks to drive her again.

It may be wise to have a couple of vacuum check valves and also make note of which hole plenum bolts was removed from and clean the bolt threads before reinstalling them. It's pretty easy to strip the threads in the injector housing.

I replaced all 16 injectors 3 months ago and the result was astounding!:cheers:

[Z51JEFF]

His car does not have that as the EVAP system is in the front of the car.

.........................................Never mind:-D

[DTZ ZR1]

Thanks for the info, I will be careful with the bolts.


DT

[tomtom72]

DT, I have a 90 so I would like to pass this possibility on to you as a fwiw. This relates to the fuel lines and block at the right rear of the plenum. The two fuel lines that come up from the frame go to a block w/ two T45 torx bolts. That block is the start of the under plenum fuel rail system.

On my car the lines at this block were in the way of me getting the Torx bit squarely on the last plenum bolt. Bleed the pressure off, and loosen the two t-45's on the block enough so you can swivel the lines enough to get on that plenum bolt squarely. You could just remove the two lines from the block if you like. Either way, the lines maybe in the way of the last plenum bolt. I don't know if it is just my car, it could be. Just thought I'd mention this as a caution.

:cheers:
Tom

[jonszr1]

have the same issue on both my 90 and 92. i just pull the fuel fitting and be done with it .

[ZR1Vette]

There is no way to get to the last torx bolt for the plenum without moving the fuel rail feed line... I would strongly recommend removing (not just 'moving') entirely (very easy to do). If you bung up the fuel line they are NLA and are rare as hens' teeth.... I know...my feed line had a defect and was lucky to get one from Kurt White.
Here you can see the line disconnected and just sitting in place and the torx bolt clearly accessible... also shows the extrusion defect (red arrow) which allowed fuel to seep thru the line and drip onto engine>>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1returnfuellinesplit.jpg

[Jeffvette]

There is no way to get to the last torx bolt for the plenum without moving the fuel rail feed line...


Michael, every car is different. Some you have to remove the pipe or at least undo the screw a little bit. Other cars you don't. If you do remove it check the o-ring as they are always destroyed. Also make sure you have bled pressure out of the rail, either by using the schrader valve or letting the car sit for a long period of time.

[DTZ ZR1]

Brothers, I have taken the Plenum off, it took about 2.0 hours. I had some help from my 10 year old son and 12 year old daughter. I am trying to get them interested in cars. Daughter loves Vettes and son likes Mustangs, enough of that.

Tom, I did remove the fuel lines, made things easier.

The ignition module plugs were interesting to say the least, can not wait until I put them back on.

I do have a question, how can I tell if I have the original injectors? I attached some pics for you all to look at and see if there is anything else I need to check. I was really wondering about the secondary actuators.

To remove the injectors do I need to remove the fuel press regulator? I am going to remove the coil packs bracket and all for cleaning purposes. What about the crank case vent valve cover, should I remove that too?

Again, thanks for all the info.

DT
614

612

[Jeffvette]

Brothers, I have taken the Plenum off, it took about 2.0 hours. I had some help from my 10 year old son and 12 year old daughter. I am trying to get them interested in cars. Daughter loves Vettes and son likes Mustangs, enough of that.

Tom, I did remove the fuel lines, made things easier.

The ignition module plugs were interesting to say the least, can not wait until I put them back on.

I do have a question, how can I tell if I have the original injectors? I attached some pics for you all to look at and see if there is anything else I need to check. I was really wondering about the secondary actuators.

To remove the injectors do I need to remove the fuel press regulator? I am going to remove the coil packs bracket and all for cleaning purposes. What about the crank case vent valve cover, should I remove that too?

Again, thanks for all the info.

DT


DT, to remove the injectors, just remove the fuel lines going into the junction block and then undo the 4 mounting bolts going into the injector housing. Then pry up.

You probably should remove the coil pack grounding plane and the starter as I can see the crap in the V of the block. You need to clean everything around the breather box before removing it, then find a solvent tank or just use brake kleen on the breather box itself. You'll have to remove the secondary linkage to get the breather box out.

The injectors are originals.

[tomtom72]

DT, looks like mine when I pulled the plenum. What a mess I had from loose cover bolts. Listen to Jeff.

AutoZone, I guess any parts store, sells the hard vac line in small spools along with the connectors so you can actually make a new vacuum spyder if you feel the need. The stuff bends & can be shaped with a hair dryer.

I'd r&r the wires and coils. The box cover bolts are proly finger tight like mine were. All the mess was in my valley and my baffle box was clean, oh, the cover hoses maybe all hard and some where here is a thread about which radiator hose to use to make them. I used 19 lbs for them going back in with an circle pattern. Don't know if that was right, but mine hasn't leaked since.:dontknow:

Test the actuators, they should either start to open at 8" Hg(?) and fully open by 12" Hg(?), and the movement should be smooth & linear. Yours look like mine did, I think they are in upside down which is okay if they still hold vacuum and have smooth movement leave them in that position as the diaphrams have taken a "set"....which you don't want to mess with....or you can buy new ones, but they need to be tested as the springs on some were installed wrong and they don't move freely if installed correctly. Sometimes you have to put them in upside down to get them to work smoothly.

Not to spend your money, but I would r&r all the injectors at this time, JMHO. Don't forget to check all the ground connections at the back of the block. You can see them easily now. Get a tube of dielectric grease and some star washers, and r&r the grounds, clean them & use the Di-electric and a star washer going back. The grease works well to service the rubber gaskets on all the electrical connectors and a dab in the pins is good also before plugging them back together.

Another caution: if you take apart the horn from the T/B for cleaning reasons....Do Not Use Carb Cleaner! Use Throttle Body Cleaner Only in the T/B. You do not want to ruin the DAG inside the T/B as it seals the butterflys against the T/B bores to close off stray air bleeding so the IAC can do it's job. Oh, and clean the IAC pintle & bore too. Don't be alarmed at the amount of liquid oil in the intake tract, that's sop for an LT5. Catch can is a good addition for that situation.

You're doing well, and the helpers are a great crew!:thumbsup:

:cheers:
Tom

[ZR1Vette]

Your doin good.... Jeff and Tom have covered things in comments...removing fuel rail/injectors... key is you want to remove the fuel rail with the injectors attached thus what you will be doing is removing the injectors from the injector housing seats. Again, using a simple tool such as shown here>>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1fuelliftingtool.jpg

just work front to rear and rear to front gently and slowing prying up a little at each pry spot and injectors will slowing unseat. Do NOT just pry up at one spot until injectors pull out because you take a chance to pulling an injector from the fuel rail which means you could damage the injector seat clip holding the injector to the rail...in this pic the clips can be seen where the injectors seat into the fuel rail.

http://i17.photobucket.com/albums/b79/MRBLU/ZR1newinjectorsinstalledinfuelrails.jpg

You will need (as in a strong suggestion) to replace the O rings for the primary injectors ONLY (secondaries come with O rings as part of the injectors themselves)... I use a tool (Sears) as shown to carefully pull out the O ring...then clean seat with cloth soaked in parts cleaner...then install new O rings.
http://i17.photobucket.com/albums/b79/MRBLU/ZR1removingprimaryinjectorOringII.jpg

Found a little trick (for me anyway) to re-install the back two ignition module plugs... after you lay down the plenum and install the two front ignition module plugs and prior to reconnecting the front (under the plenum) vacuum line simply push forward the plenum slightly (as shown here)>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1ignitionmodulerearplugs.jpg

and install the plugs (that little 1" movement forward makes getting to the plugs etc sooooo much easier)...once plugs are installed then slide plenum back into position and slightly lift front of plenum to install the vacuum line.

Hope this helps a bit

[DTZ ZR1]

Just finished up with putting everything back together. Changed plug wires, coil packs, injectors and cleaned up the valley. Thanks for all the info, you all made this job very easy for me.
The car runs great, I did not have time to take it out. I will tomorrow if the weather is good. Again, thank you all.

DT

[flyin ryan]

Just finished up with putting everything back together. Changed plug wires, coil packs, injectors and cleaned up the valley. Thanks for all the info, you all made this job very easy for me.
The car runs great, I did not have time to take it out. I will tomorrow if the weather is good. Again, thank you all.

DTAwesome, that's great so far ;).

[tomtom72]

:thumbsup: Schweeeet Deal!:mrgreen:

[Kb7tif]

Your doin good.... Jeff and Tom have covered things in comments...removing fuel rail/injectors... key is you want to remove the fuel rail with the injectors attached thus what you will be doing is removing the injectors from the injector housing seats. Again, using a simple tool such as shown here>>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1fuelliftingtool.jpg

just work front to rear and rear to front gently and slowing prying up a little at each pry spot and injectors will slowing unseat. Do NOT just pry up at one spot until injectors pull out because you take a chance to pulling an injector from the fuel rail which means you could damage the injector seat clip holding the injector to the rail...in this pic the clips can be seen where the injectors seat into the fuel rail.

http://i17.photobucket.com/albums/b79/MRBLU/ZR1newinjectorsinstalledinfuelrails.jpg

You will need (as in a strong suggestion) to replace the O rings for the primary injectors ONLY (secondaries come with O rings as part of the injectors themselves)... I use a tool (Sears) as shown to carefully pull out the O ring...then clean seat with cloth soaked in parts cleaner...then install new O rings.
http://i17.photobucket.com/albums/b79/MRBLU/ZR1removingprimaryinjectorOringII.jpg

Found a little trick (for me anyway) to re-install the back two ignition module plugs... after you lay down the plenum and install the two front ignition module plugs and prior to reconnecting the front (under the plenum) vacuum line simply push forward the plenum slightly (as shown here)>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1ignitionmodulerearplugs.jpg

and install the plugs (that little 1" movement forward makes getting to the plugs etc sooooo much easier)...once plugs are installed then slide plenum back into position and slightly lift front of plenum to install the vacuum line.

Hope this helps a bit

Hello can you yell me about how far down in the housing are the seals for the primary's?

[tomtom72]

I'm guessing you're referring to the early style 90-92(?) primary injector O-rings like the one in the picture by Mike?

If so, then if you look at your I/H primary holes, the O-ring is just below that polished area. Maybe 3/16" below the top surface.


Any Help?

[ZR1Vette]

For a picture... primary injector site on left still has O ring in it and the one on the right is removed and you can see the O ring seat area>>
http://i17.photobucket.com/albums/b79/MRBLU/ZR1removingprimaryinjectorOringI-1.jpg

[secondchance]

Just finished up with putting everything back together. Changed plug wires, coil packs, injectors and cleaned up the valley. Thanks for all the info, you all made this job very easy for me.
The car runs great, I did not have time to take it out. I will tomorrow if the weather is good. Again, thank you all.

DT

Terrific!:thumbsup: