1990 LT5 368 with stage 1 cams performance issues

[blr33439]

I started this post to get some assistance with the 1990 ZR1 I just bought from Houston, TX. Here are the basic details on the car from the previous owner:

ENGINE:
368 LT5 with stage 1 cams from SGC
JE pistons and Manly billet rods
aluminum radiator
ceramic coated SSworks headers
triflow 3 inch pipes
dynoed at 560Hp on Coreys dyno

DRIVETRAIN:
aluminum flywheel
kevlar clutch
hurst shifter
409 gears

SUSPENSION BRAKES:
coilover shocks
urithane bushings
camber brace
upgraded anti roll bars
Willwood 13inch front brakes

BODY:
greenwood GC4 centerline down body kit

Now for the issues:
The car runs great WOT but bogs down really bad below 3000RPM. From a start, it will bog and nearly die if I don't use a lot of clutch and start above 2000rpm. Above 3000RPM the engine is smooth and has lots of power. The original owner stated that it bogged below 3000rpm since he has had it, even when properly tuned. I have heard from other lt5 owners with similar mods and stage 1 cams that this is not normal.

Now here is my question:
-What are some likely causes so I can start troubleshooting. I have a reasonable selection of tools and can normally justify new tools. I also have the LT5 shop manual on order.

-Other recommendations?

-I am in Groton, CT if anyone is close.

Thanks,
Brandon

[tomtom72]

Hi Brandon and welcome to our corner of the asylum!

I'm relatively close down here in NYS near the CT border by Greenwich. The only thing I can offer is the use of a scanner with '90 software and maybe the fuel numbers might give a hint of what's going on. I have a snap-on MT2500.

I'm not well versed in LT5-ology on modified motors. There are a few guys like the FBI group that know quite a bit about using different cams in an LT5. One of them will see this for sure and come over to assist you.

:cheers:
Tom

[ZZZZZR1]

Brandon,


Saw your post on the CF and you will get tons of advice. I would talk to the last person that worked on the car first.....

See what was done and if it had issues then. You got a HELL of a car and when it gets done, you will be one happy customer.

Do you know what tuner had it last?

Congrats on your purchase!


:cheers:

David

[Bob G]

Exhaust cams are to big

[blr33439]

Last tune that I know of was by Corey in Houston(Info from the last owner).

I did a test run today with the key in the low power mode to see if it ran different. It ran a lot smoother and I was able to cruise on the highway at 2000-2500RPM. It was still a little rough and did not want to accelerate on the highway from 2000RPM, but it was much better than in full power mode. I put it back in full power and made another test drive. Same sub 3000RPM issues but great at full throttle. Tried to go sideways on the highway from 60mph in 3rd. Does this help narrow possible issues.

Are there any common issues that I should check first.

[A26B]

If Corey had it last, it won't be a problem with the tuning. He wouldn't let a car out of
the shop with a tuning issue like that.

It sounds like a closed loop problem, assuming the tune is not an "open loop only." With a standard closed/open loop tune, the ECM transitions to open loop at about the rpm where yours starts to run good.

Before anything else, disconnect the battery for a few minutes to clear stored DTC's (diagnostic trouble codes), then reconnect and drive the car to re-create the problem. Check for newly set codes and record.

If there are new DTC's stored, post them here and we will help you resolve them accordingly. Always start with the lowest numerical DTC first.

Likewise, if there are no newly stored DTC's, we can help you with the next logical steps. Taking shortcuts often means doing a lot of unnecessary work.

I would take Tom's offer to help with the scan tool. He knows how to acquire the data and take the next logical steps. Approach the problem as you would a stock engine. SGC Stage 1 cams are not the problem.

[blr33439]

I am still waiting for my service manual to arrive and the ZR1 trouble code reading proceedure is not easy to find online. Can anyone point me to a good reference article or posting for how to display the trouble codes on the 1990 zr1.

[Pete]

It's so hard to try and figure out what the issues of a car are on the net.

Couple of questions.

Any codes?
What does it do below 2000 rpm when cruising?
Does it feel like a miss/dead cylinder or does it buck/chug?

First check the common issues
Injectors
wires
plugs
coils
If all checks good.

Other reason why it would buck/chug below 2k rpm,too lean or too rich,put a wide band on and check AFR's at 1500-2500 rpm cruise.

Pete

[ScottZ95ZR1]

I am still waiting for my service manual to arrive and the ZR1 trouble code reading proceedure is not easy to find online. Can anyone point me to a good reference article or posting for how to display the trouble codes on the 1990 zr1.

http://www.zr1.net/forum/showthread.php?t=7820
http://www.zr1.net/forum/showthread.php?p=96577
http://www.zr1.net/forum/showthread.php?p=108140

[blr33439]

Ok. I disconnected and reconnected the battery. Plugged in the code reader. Code 12: No codes.

Symptoms low RPM cruising. It feels like there is a lack of power when climbing. When giving it more throttle, it hesitates and then kicks in.

[Kevin]

does the car still have the secondaries in?

[QB93Z]

Hi Brandon, welcome to the Registry Forum.

I have a 1990 Lingenfelter 368 with modified cams and a set up similar to yours except mine has stock dual-mass flywheel and stock 3.45:1 differential.

I notice, to a smaller degree, some of the low rpm performance issues that you have described. The engine seems to have less power below 3000 rpm than my stock ZR-1's.

That being said, for your description, I would investigate possible faulty primary injector just because it is a 1990.

Despite the low rpm performance issue, the car is a a solid performer on the drag strip. Best 1/4-mile so far is 12.26 at 120 mph.

Good luck and enjoy.

Jim

[blr33439]

I contacted the previous owner for some additional information. The car was running well after Corey tuned it(several years ago). The secondary injectors were replaced approximately 5 years ago but the car has been sitting. Unknown status of primary injectors. The cams are stage one from South Georgia Corvette.

My initial instinct is leaning toward bad primary injector(s). Any recommendations from here. Best source for injectors and appropriate size for this engine.

[ZZZZZR1]

FIC. www.fuelinjectorconnection.com


Call John Banner. Ask for stainless steel injectors

:cheers:

David

[A26B]

I contacted the previous owner for some additional information. The car was running well after Corey tuned it(several years ago). The secondary injectors were replaced approximately 5 years ago but the car has been sitting. Unknown status of primary injectors. The cams are stage one from South Georgia Corvette.

My initial instinct is leaning toward bad primary injector(s). Any recommendations from here. Best source for injectors and appropriate size for this engine.

I would agree with your instinct and would seriously consider a complete set of 16 new SS matched injectors from Jon at FIC. I have yet to hear of successful, long term results from repalcement of just some of the injectors.

Let me know if I can help you with any gaskets or seals. Jon/FIC now keeps Jerrys Gaskets & Seals in stock so you can get the whole, turn-key package from him.

[blr33439]

I looked at the injector options on their webpage
http://www.corvetteinjectors.com/shop/viewcategory.php?groupid=3
I see that they are all flow matched.
How much difference is there between the three options they have for 1990-1992. I noticed there is some price variability. Any opinions on ideal flow rate for the engine combination I have. Also, what gaskets am I likely to need for the upcoming work.

[A26B]

I would get these:
http://www.corvetteinjectors.com/shop/viewitem.php?productid=32

Stock injector flow rates will be more than adequate for your engine.

For the injector replacement, Jon, will have everything you need regarding gaskets & seals, set of plenum gaskets, primary injector lower seals, fuel feed & return block seals and the fuel pipes to regulator & rails seals. The injectors come with all the seals for the tops and the bottom of the secondaries.

[blr33439]

I pulled the intake today. The secondary throttle bodies are still in place. I tested the injector resistances(15 at 12ohm(normal) and 1 at 9.8ohm(bad) but it was a secondary injectory). I pulled them completely but found no obvious issues. Anyone ever sent injectors in before rebuilding or buying new. I don't want to spend several hundred dollars to still be chasing the problem.

[Kevin]

normal is 12.5-15 ohm, you have a second one going bad

[-=Jeff=-]

normal is 12.5-15 ohm, you have a second one going bad


And more will follow suit.. the 90 injectors don't like ethanol. if you want to save some $$ you can buy FIC rebuilts, they have a 3 year warranty..

I have these on my 90
http://fuelinjectorconnection.com/shop/index.php?_a=viewProd&productId=165

[Pete]

And more will follow suit.. the 90 injectors don't like ethanol. if you want to save some $$ you can buy FIC rebuilts, they have a 3 year warranty..

I have these on my 90
http://fuelinjectorconnection.com/shop/index.php?_a=viewProd&productId=165



Wow nice price.

I agree with Jeff change them all,and do the job once they will start to go out one at a time.

Pete

[blr33439]

I spoke with John at corvetteinjectors.com today and he was very helpful. I ordered the New Lucas injectors and should have them in a few days. I will post an update once the install is complete. Any other recommended maintenance or inspections while I have the plenum off.

[Kevin]

I spoke with John at corvetteinjectors.com today and he was very helpful. I ordered the New Lucas injectors and should have them in a few days. I will post an update once the install is complete. Any other recommended maintenance or inspections while I have the plenum off.

if the wires need changed do that, check the drain hole in the V, it gets junked up. And whats the deal with your av...it looks like a c4 headlight but not

[-=Jeff=-]

if the wires need changed do that, check the drain hole in the V, it gets junked up. And whats the deal with your av...it looks like a c4 headlight but not

it is his new headlight big thread at CF about it

[blr33439]

Good idea. I think the plug wires are fairly new so I will check them with the multimeter(what specs should I expect for good condition). Also, what is the best way to check the coils? I already pulled a couple plugs to check the condition and they looked ok. The previous owner said the engine has eaten a few plugs in the past(don't know if this is normal or caused by other factors). Recommendations on plugs?

[blr33439]

I reinstalled the new fuel injectors and the fuel rails yesterday before the sun went down. I have a question on the three electrical connectors that attach under the intake plenum. The only part designation I could find was 6ped and 7ped. Am I looking in the wrong place for part numbers or is there a corresponding number. I want to replace the connectors since they are brittle and one clip broke upon removal. I have looked at several online connector websites, but I don't think I have the right part number.

[QB93Z]

I have also been trying to find the correct replacement for the Ignition Module connectors, but I haven't had any luck so far.

Here are the connectors for a 1990:
http://i407.photobucket.com/albums/pp152/QB93Z/Elec%20Conn%20Repair/DSC04386.jpg

http://i407.photobucket.com/albums/pp152/QB93Z/Elec%20Conn%20Repair/DSC04388.jpg

The later model LT5's also have a connector for the Secondary Vacuum Pressure Sensor.

Please let us know if you find anything.

Jim

[FU]

Google search is your buddy.
http://www.repairconnector.com/categories/ENGINE-SENSOR-PIGTAIL-CONNECTORS/

Providing the connectors are not in real bad shape. Sometimes they can be held together with a tie strap or two.

[blr33439]

Starter went. Hear a high pitch spinning but it is not engaging the motor. Anyone know where to get a rebuild kit?

[sammy]

have used the napa rebuilt starters in both my cars with great success . price is reasonable too

[Paul Workman]

Google search is your buddy.
http://www.repairconnector.com/categories/ENGINE-SENSOR-PIGTAIL-CONNECTORS/

Providing the connectors are not in real bad shape. Sometimes they can be held together with a tie strap or two.

Thanks for that link, Frank. Maybe an item for "Solutions", eh Cliff??

(Oh, and do you have a link for the tie wraps too?.....JK!;))

P.

[Pete]

Did the injectors fix your issue?

Pete

[blr33439]

The new injectors made an improvement but it is still not running perfect. I will give the computer some time to recalibrate before troubleshooting further.

[blr33439]

After pulling the starter, found out it was already a rebuilt unit. 40k miles, now that is dissapointing. My Bosch rebuilt starter arrived today and I got a couple sets of gaskets from Jerry so now I am waiting for decent weather this weekend. Anyone know what is used to attach the coolant T's to the intake manifold. It kinda looks like an epoxy, but I wasn't sure if there was a specific type to use.

[Paul Workman]

After pulling the starter, found out it was already a rebuilt unit. 40k miles, now that is dissapointing. My Bosch rebuilt starter arrived today and I got a couple sets of gaskets from Jerry so now I am waiting for decent weather this weekend. Anyone know what is used to attach the coolant T's to the intake manifold. It kinda looks like an epoxy, but I wasn't sure if there was a specific type to use.

JB Weld will do. But, unless you are going to be driving in sub zero weather, you can drill and tap and plug the TB coolant ports in the IHs. That way if and whenever you need to pull the plenum off, you don't have to fuss with draining and refilling the coolant, AND the plenum and TB will run a LOT cooler - not a bad thing, performance wise!

Just a thought.

P.