Help!! 91 missing/underpower issue

[SDZR-1]

Ok...been experiencing this for about 3 days now...pulled codes and only found throttle position sensor to be too high but it was only showing .3 volts. service engine light came on twice today for about 5 seconds each time. to describe it best there is a clattering sound (sounds similar to a lifter clattering) that comes from underside of engine (maybe tranny, I cant tell for sure) that goes away with a bit of throttle. it is also missing and has less than superior power, although I can feel the secondaries open up at full power. I have spark to all plugs. I dont know what else to check, any tips would be greatly appreciated. Also, fuel mileage seems to have dropped quite significantly.

thank you
Jarvis Bruhn

[gbrtng]

Ok...been experiencing this for about 3 days now...pulled codes and only found throttle position sensor to be too high but it was only showing .3 volts. service engine light came on twice today for about 5 seconds each time. to describe it best there is a clattering sound (sounds similar to a lifter clattering) that comes from underside of engine (maybe tranny, I cant tell for sure) that goes away with a bit of throttle. it is also missing and has less than superior power, although I can feel the secondaries open up at full power. I have spark to all plugs. I dont know what else to check, any tips would be greatly appreciated. Also, fuel mileage seems to have dropped quite significantly.

thank you
Jarvis Bruhn

Pull the spark plugs - bet you find a bad one ...
What is/are the SES code(s) ?

[tomtom72]

The clattering may be a loose heat shield....I have one & at the right rpms I hear it & then it quiets down once I pass the resonance spot.

Miss....all the time or no? Checked the whole ignition system; plugs, wires, coils all are good. Did you pull any plugs to see how they are burning? Did you scan it to look at the fuel numbers? Did you scan to check the CCM for any history codes?

Gas milage going south + a miss; I say you will find something on a scan, JMHO. Are the injectors the OEM set? Remember 90 & 91 are not ethanol proof. When you get to the secondaries the miss goes away? Does she smell lean or rich out the exhaust at idle? Forgot this, how's the fuel system; pumps, regulator & filter?

FSM, section 6E, drivability & emissions is a place to start looking up your symptoms. There is also a page there with scan data for a normal LT5 in closed loop.

:cheers:
Tom

[SDZR-1]

yes...it misses all the time; at idle and while driving. I will pull the plugs today and check that. From what I had been reading, it sounds like it could be the primary injectors....which I think I will change regardless when I put in my new starter since I believe they are oem....either way, I would still like to determine the problem before hand. thanks for the replies guys, and keep any other suggestions coming...I definately appreciate the feedback.

[tomtom72]

Okay now we're getting somewhere! If it misses all the time my next Q will be;

does the miss get worse as the motor comes up to proper operating temp?
If yes then it's not looking good for the OEM injectors.

Q2; Do you know what a lean condition smells like? Stand behind the car & get a good wiff of the exhaust...if it makes your eyes water &/or smells kind of acrid then ya have a lean burn....bad injectors, maybe.

Q3; did you run down any DTC's? Post up if you have them.

Q4; do you have a scan tool, need that to look at the fuel numbers. Oh, and a FSM. :thumbsup:

Q4; Did you pull any plugs & take a look at the burn pattern? Do they look too clean, do they look dry, like they saw no gas? If so the fuel filter is blocked solid or the primary injectors have coil failure. Outside shot could be the injector drivers in the ECM, or maybe bad injectors relays. You have good fuel pressure?

FWIW, you can test the ohms reading on the injectors thru the ECM harness but ya need the FSM for the pin numbers. I believe above 16-18 ohms is okay but don't quote me on that one. Oh, if you ohm them you should do them stone cold and after the motor gets hot. Usually they break down more severly the hotter they get.

My guess....just a guess mind ya...is the primaries sound like the have died & gone to meet their maker.:o

:cheers:
Tom

[SDZR-1]

no...dont have a scan tool. but had a guy i know plug his in and all it came up w/ was that code 21 throttle position sensor too high. I found a fouled plug after pulling them out, so tomorrow I will just replace all of them and go from there...i'll let you know, thanks again

[tomtom72]

Okay cool! Was that fouled plug wet also? Only one plug then chances are the coils are okay and the wire to that plug maybe a suspect....maybe or the primary injector on that cylinder is leaking....those are the only two explanations unless the gap got crushed on the way in.

Try the new eight & let us know if the miss quits. :thumbsup:

I hate to keep repeating this, sorry but it's important. Do you have a FSM for your yr. Z? If not you should add one to your tool box, Helminc.com.

If you get to borrow your buds scaner again run the display with the motor running at idle from cold to hot and make note of the fuel trim numbers. Reason I say to do that is it lets you see what the ECM sees and that data will tip you to any combustion issues.....even if the injectors are shorted &/or leaking. Like I said there is a page in the 6E section of the FSM showing typical closed loop data as a metric to compare your motor against.

:cheers:
Tom
sorry forgot this, our TPS's are adjustable. Engine off/key on and a scaner or a DVOM hooked up to the TPS terminals and loosen the hold down screws and rotate the TPS till ya get the correct 0.54v....the FSM gives the range that's okay....but 0.54v sticks in my head.

[SDZR-1]

yes...i do have fsm's for my car I will check the 6e section tonight to find what you are talking about. I live in a tiny little town here, so it's gonna be a few days before I can get all the parts I need. I seriously cant get spark plugs til thursday...sad but true, haha. I've also got a starter coming as well...is there anything that I should know about changing that, or is there perhaps a write up on it somewhere? thanks, Jarvis

[tomtom72]

Geeze & crackers.....that is a pia about getting parts!

What's up with the starter? Can the starter wait? MHO, get the new eight & try her out just so you don't really bury the true diagnosis and the lessons there in.

Section 6E: Emissions and Driveability. That is the EEC system from top to bottom....or at least 6E is listed as that in my 90 FSM.

Write ups that may be of use:
Corvette action center.com and go to their zr1/callaway/C4 section.
Jeffvette's PacificNorthwest ZR-1 Chapter has a site with great how to's.
Big Country Corvettes.com is the TX chapter's web site.
Search our own forum & you'll find my thread when I was a real nooooob & had to swap out my injectors....that thread should be good for a few chuckles!:sign10: :rolleyes: :redface:
Our own netreg site in the maintenance section also has some useful write ups.

Parts via the internet:

partszoneonline.com, P & G Chevy in PA, my personal fav!:mrgreen:
Superior Chevrolet
Tom Henry Chevrolet.....the last two are listed over at the netreg site with contact info.
You know whiteracing.com, and check out jeffvette's new site, pnwzr1.com and RCEngineering.com, Accel.com is the new place for injectors if ya don't want to just have one place to buy from. I used RC's & I am happy but alot of the guys have used the accel's and are happy. Search our forum for the threads.

Chit if I would have known I would have sent you a set of eight! I keep spares as I use the plain old GM replacements for the FR2LS's...hard to find in the auto parts stores where I am....I forget the p/n.

:cheers:
Tom

[SDZR-1]

so i still dont have parts yet...but always feel the need to give my car a little attention, so decided to wash it. I attemp to start it up and it misfires and does the whole pop bang cough thing since it is running so rough and dies. I also noticed a puff of smoke coming from around the fuel pressure regulator...could have been under the plenum and just exited near the regulator....i dont know. Anyway, I definately smelled fuel just after. Just figured I would share that, thinking it might spark something that could determine my problem.

As far as the starter, it does need to be changed...I can get it to start but sometimes it takes up to about 30 attempts to get the starter to go. So anyway, I should have plugs tomorrow and will install them, then report back. My starter wont be here til friday anyway, and injectors not til monday....so maybe we can pinpoint this in the meantime. Thank you very much for the helpful advice so far.

Jarvis

[tomtom72]

Jarvis, that smoke from the back of the plenum is the MAP sensor hose not connected to the MAP or the plenum nipple.

That will cause a god awful miss if it gets blown off. Next to the regulator is the MAP. It's right in the middle of the back end of the plenum.

Jezze I really feel stupid now!:o
My apologies to ya man! That hose being off will cause the car to carry on the way you have described it. Reach down there & feel around & reconnect the hose. From the passenger side it might be easier to snake your hand down past the MAP bracket. I'm short so I kneel up on the right front tire & kind of crawl half over the motor to get my hand down there.

Go check on the MAP hose & try to get her to start & see how she behaves. Oh, I assume that you hunted up the threads we have on "no start" conditions. VATS, clutch saftey switch, ignition switch wires breaking off inside the collum, starter enable relay, Look up here & over at the netreg site.

:cheers:
Tom

[SDZR-1]

Ok...changed plugs at noon today and checked the line going into the back of the plenum and everything looks good. After swapping plugs I did not notice any difference. Although when i pulled them the other day I found that single plug that was real wet...I cleaned it up and dried it off before I replaced it; when i pulled it out today it was soaked again. Does this mean that perhaps that wire is bad and that it isnt sparking at all?

[A26B]

Not likely, but easy enough to check. Put an old plug in the wire & lay it on the plenum, start the engine & check for spark.

Most likely, particularly if you have spark, is a bad injector. Could be either primary or secondary.