Sputters & misses

[tomtom72]

Hi All, any opinions are welcome! I'm a rookie at ECM & FI cars & ZR-1's. My 90Z has a sputter &/or miss but it starts up & runs, no SES light. I did the following:

Looked for codes in ECM & CCM, none in either place. Used Gordon's jumpers.

Pulled all the plugs, 1-7 plugs were charcoal on both electrodes & center porcelians. Even # plugs were charcoal on both electrodes but center porcelians were snow white?? No fouling, deposits or crud or broken stuff or raw gas on any of them. My observation, entire even # bank is lean??

I then did a Fuel pump pressure test using chart A-7 in Helm. My results:
KOEO, FP2 fuse pulled, 44PSI. PSI holds for 15 min., then I released it.
KOEO, FP2 fuse in place, 44PSI. PSI holds for 15 min., then I released it.
KOEO, FP1 fuse pulled, 44PSI. PSI holds for 15 min., then I released it.
Engine idling, both fuses in, water hot, PSI 42 to 44, gauge danc'in severely in that 2PSI range. Shut down & PSI holds for 15 min., then I released it. Book says good pumps are 48 - 55 PSI on all tests, and should hold steady after pumps are off but book doesn't say how long they should hold PSI.

My interpretation of results: Both pumps are weak? Both pumps are weak by exactly same amount?? The only thing they have in common is pressure regulator, could regulator be bad??? All the even bank injectors are bad along with the pumps & regulator. I wouldn't have expected to see the gauge dance with the engine running? No fuel in the Vacuum hose on the regulator & the hose seals well. I replaced the MAP sensor hose just to make sure of a good seal, no dice. I swapped out F filter, no dice. I will pull some vacuum on the regulator & MAP just to see. I swapped in plugs, no dice.
I don't have much faith in my diagnostic abilities so I don't know what to make of the fuel pressure tests. My eyes tell me it's a lean condition but I just don't know.
I'd be greatfull for any input, thanks. Sorry this post is so long!
Tom

 

[Aurora40]

I'd think it would have to be at least the pressure regulator, it seems that if the pumps were weak, they wouldn't be right around the same place all the time, but would go down and up a lot as the load/etc changes. Just a guess, though.

Also, with the engine idling and the coolant hot, isn't only the primary pump working?

Disclaimer: I'm just a guy who thinks too much, not an ace at troubleshooting things (well not cars anyway).

 

[tomtom72]

Hi Aurora40, Yes the FP2 shuts off after the coolant temp gets to a pre set point. I'm not exactly clear at what point. That's why I pulled the fuse on FP1 so I could read the PSI from pump 2.

I agree with you that it's strange that both pumps read exactly the same! But I re-read the Helm, it takes awhile to sink in with me, and my take on the regulator function is it can't cause a lean condition. The Helm book says if it fails a rich condition happens. It's a simple vacuum brake & if it fails the spring weakens or more likely the diaphram leaks. If it leaks I would think I'd see fuel in it's vac hose, no fuel in my vac hose.
I know that tomorrow I'm getting another new filter & redo the PSI tests just to be sure.
Thanks for taking the time to throw some thoughts my way !
Tom

 

[gmjunkie]

If it was a vac. problem on that eng., the lean cond. would be on all cyl.!! ( I would Think!) What about the spark plug gap were the plug's gaped wider on 1 bank than the outher, ck and see! If so is lean cond. on wider side? If so I would think a new set of plug's gaped right mite be in order, if not I'd put it on a computer and start checking for weak Oxy sencer's or a cat restricted!! Wat's kind of Vac. duz it pull?? Duz vac. gage flucuate?? I think your fuel pump's and Reg are allright!! As far as low pressure I think your gage may be a little off!! (not unusual) You can't find 5 new tire gages the same anymore!! I'v had Fuel Pump's hold press for day's!! Hope I helped ya!! junk!!

 

[tomtom72]

Hi Junk! I hear ya about the gauge, I'll try another. I bought a new one when I got the Z. I didn't do a vacuum test but I will. Plug gap eyed okay, I'll put a feeler gauge to'em though. I was absent when this EEC stuff was developing. So I'm way behind on understanding the function of all the "stuff" on a EEC system & what it's supposed to be doing. I'm way behind the curve!

Just for S & G's I'm gonna swap in a new fuel filter & plugs & redo the tests. Shoot'in from out my arse...One bank can't be lean & the other be okay, if so what's the issue. Fuel delivery? Plugs ain't wet & not fouled but one bank is lean on FI car all the injectors on one bank failed at once??? not likely. Pumps fail &/or get bad/weak at same time by same amount of PSI loss??? not likely. Helm says bad PSI reg.= rich. THE O2 sensor I never thought of, one on each bank; it's the only device that could effect only one bank at a time. Do I get the theory right? I don't have an O2 code but I'm not sure what sets an O2 code. I'll go read up on O2 sensors. I looked at the injector balance test in the Helm book & thought dealer time. No Tech1-A in my tool box. Oh & I guess I'll dig up my inductive T/light & check all the plug wires to see what kind of pulses exist. 'Tween that & my Vac gauge...those were my two favs. to diagnoise my 72 C3; but we're along way from there w/EEC I guess?
Thanks for the thoughts & your time, Junk!! I apologize to everyone for thinking out loud on this forum...I'm one of those people that has to.
Tom

 

[gmjunkie]

Look close!! some vehicles have 2 oxy senser's on ea. side Before Conv. and aft.!! I don't know on your's, My 03 has 2 on ea. side!! The aft. one's you can hardly see,thay are in the tunnel behind conv.'s on top!! Junk!!

 

[tomtom72]

Hi Junk, Just looked up O2 sensors in my Helm...only two, one on each side, the three wire type. If I understand the ckt dia. right: each has a ckt from the ECM, one connects to the other thru a ckt, and each has a ckt for a heater. I guess a scan tool is used to get real time ohms & such so you know they are within spec? I got to study on this some before I go poking around. I think I'll try reading the whole code section in Helm & maybe get a hold of the relationships of all the parts. No use poking around in the dark. If I don't understand what all the peices are responsible for & how they are supposed to work in a closed system I'll be going in circles. Gotta go back to work now. Thanks for all your input, straight up man I'm greatful to ya!!

Tom

 

[Aurora40]

I guess a scan tool is used to get real time ohms & such so you know they are within spec?

I still have a set of test connectors I bought from MidAmerica about 5 years back. They are sensor connectors that have extra test leads coming off them. So you can test/monitor the sensors with a regular multifunction test tool (ohm/voltmeter) without having to pierce any wires or anything.

I don't know if they still sell these or sell them for the LT5, but that would let you monitor the output of those sensors without a scan tool.

 

[tomtom72]

Cool piece!!! I'll go over to M/America & look.

Thanks Aurora!!!!
Tom
(I should just drive it to the dealer & have them put it on the service bay diagnostic machine. I have the feeling I'm going no where fast.:W It's just I hate to give up & get beat! Should have gone to G K's school before I bought the car!)

 

[tomtom72]

Update

I re-tested fuel PSI w/new F filter. KOEO tests = 50 PSI & idle speed test = 45 PSI. Engine vacuum @ idle = 15" hg, all readings rock steady & still no SES light. I think reading the spark plugs are confusing me...plugs are a history, not exactly real time data. I pulled the plugs to see what was happening, 7 thou on std delco replacements. I could use a new set & let it idle or even drive it a bit but I bet they tell me both banks are lean? I may do this just to see what happens.

I think the main thing the plugs told me is that they were/are firing cleanly...no fouling, no deposits and they are not getting enough fuel. Maybe also they are telling me the balance of fuel across the engine is not correct? I guess that's injector balance??? If anything the ignition has spark or they'd be wet & they're not so whatever gas is gett'in there is being burnt.

O2 sensors, at least right side one because the right bank plugs had white center porcelians but sputter is in both "open" & "closed loop". O2 signal is ignored by ECM in "open loop" mode,till water temp & O2 temps come up, right? That's the definition of "closed loop"? Sputter exists in Full power & normal power which would say all 16 injectors failed at once, I doubt it.

Does some kind of ignition computer have any input as to what the injector volume should be? Is the signal from crank &/or cam sensors germain to fuel volume delivery? I'm looking for what affects fuel volume, I think that's the root cause? Obviously, I'm lost! Any ideas?
Tom

 

[Aurora40]

I'm not sure what you mean by injector volume. But the ECM tells the injector the pulse width, i.e. how long to open for. This plus fuel pressure, as well as the injector's capacity, determines how much actual fuel is put out.

As an aside, I believe you can also read duty cycle (or figure it out) as a % of the time the injector is open. The faster the motor spins, the more often the injector has to open. Spin it fast enough, and there's a certain pulse width that means the injector is constantly open and you can't get any more fuel in (without changing pressure or the injector's capacity).

 

[tomtom72]

Injector volume is a dumb thing on my part, I know. I mean the amount of fuel delivered at each firing, or as you correctly said "pulse width". That's what I was thinking about. Just couldn't think of the right word!:ugh

I was just looking in the dark for an answer, if it were a holley i'd say clogged circuit, run or idle or intermediate or maybe a power valve or the famous holley vacuum leaks! I think I'll call the dealer in the AM & make a diagnostic appointment. I want to know what's wrong first. If it's the injectors then I'll do this myself along with everything else under the plenum. Go in once & be done with all that's under there. Then I can use it all up!

Thanks for your efforts Aurora40!
Tom

 

[gmjunkie]

I was just looking in the dark for an answer, if it were a holley i'd say clogged circuit, run or idle or intermediate or maybe a power valve or the famous holley vacuum leaks!

If it were a Holley, There'd be a Big Burnt Spot on Hood!! May be plug wire's or coil braking down~!! junk!!

 

[tomtom72]

Hey Junk!! I hear you! I must say I liked my Barry Grant Holley that I had on my 72 LT-1, worked like a charm!

Yea wires or coils, I study that closely next. The thing is that stuff is under the plenum on a LT5. This stuff makes me wish I had paid attention when my bro when he was trying to learn me about EEC systems. He was a dealer techie & he administrated the learning blocks for the other techs! I should have paid attention, I might have learned something! :ugh

Tom

 

[ZR1 MK]

I am a little confused regarding your plug readings. I think the 44 psi pump pressure isnt critical, but you may need an approx 10 second full throttle pull to get a lean code to confirm. I had one injector fail recently that required a pull this long to create the lean code. Diagnosis is so much easier when a code is present.

 

[tomtom72]

ZR1 MK Yes a code would at least give me a direction or a starting point. I never thought I would be glad to see a SES light!

I re-did the fuel tests w/a new filter & got text book readings. The plugs got that way I think because the sputter &/or miss started while I was on a run with other vettes & I was 50 miles from home. So by the time I got back they were showing the results of one bank being lean & the other bank being okay, A/F ratio wise. I'm just guessing at that conclusion being valid. I mean how else does the even # plugs come out with clean center porcelians & the odd # plugs come out looking normal? To me it seemed that odd side of the motor was getting enough fuel & the even side was not? I don't know, I guess all the primary injectors on the even cyl bank went out together? All the plugs are getting spark, the fuel pumps work okay, I'm at a loss for an answer.

The only thing I know for sure is the sputter started out very slight & got worse over about ten minutes till 2500 rpm was about all it would go without really missing so badly as to scare me off of the gas pedel. I figured I would see a SES light any time on the way home but no soap. I even tried the power key to activate the secondary injectors & the miss was the same key on or key off. I figured that would give me a code but no soap either. Not that I know much but the miss is there as soon as it starts up so I figure it isn't the O2 sensors as they are not used until water temps comes up. I checked battery voltage too, 12.5 so I know there's juice. I wiggled all the grounds at the back of the motor & they're tight. Next I guess I try to ring out each ground thru the plugs on the ECM? I tested the ohms on the primary injectors thru the ECM plug & I got 18 ohms for the entire circuit, injector + pins + wire, for each primary injector but I don't know if that's good or bad.

Thanks for the shout!
Tom

 

[ZR1 MK]

The injectors should be in the 12-13 ohms. Its far more important to test them hot rather than cold. I had two secondary injectors test ok electrically, but fail mechanically, so the electric test isnt a final sign off.
One of my primary injectors has probably been slowly failing over the years as my right block learn has been slipping to 119. Intergrators are 128 ea side and compensating for my right side rich condition. The beauty of electronics. If you had a Tech 1 like me, you would be able to monitor and test as described above. If you plan to do most diagnosis, it makes sense to invest in the equipment. Previously owned Tech 1s typically go for +- $600.
Good luck and keep us posted on any progress.

 

[tomtom72]

Mike, thanks for the heads up. It runs so badly that I can't stand to hear it run for more than 2 mins. at a time! I keep looking on e-bay but I haven't been lucky. I bailed on one after the bidding crossed $700! I'm not very sure I'd know what the machine was telling me anyway. I'm not literate with EEC. Gotta learn from the beginning, not the middle, or where ever I am now. Heck I'm lost, that's for sure! Oh well when my order from KWracing & P&G chevy gets here I'm gonna dive in blind. At $90 a reman'ed ECM was reasonable enough. I'm mad at myself for not taking Gordon's classes. I should have took two weeks & did his C4 course. Oh well I had fun up to this point and I'm sure I'll solve it before next summer!:L

Thanks for your efforts,
Tom

 

[Aurora40]

but you may need an approx 10 second full throttle pull to get a lean code to confirm.

That sounds like a pretty fun way to troubleshoot!

 

[tomtom72]

Just a conclusion for this

Hi all, As I'm a rookie Z owner and a rookie to electronic FI I thought it would be good to put a period on this tale. Just in case there are others that might run into this with their cars. If I knew more I would have figured this out but I'm learning. If I had a scanner the data would have tipped me to bad injectors if I knew how to interpret the data, I'm learning. Anyway, my case was a miss started & the car's exhaust smelled lean. I chased down the plugs, looked for good spark, tested fuel pressure, looked for vacuum leaks, no SES light, looked for DTC codes...all negative. A scanner revealed the integrators way off. The car would run but the hotter it got the worse the missing & shaking & sputtering & the more pronounced the lean smell became. If it was stone cold you had to work to hear or feel the miss, it still smelled lean though. If I was experienced I would have used the symptoms and the scan data an seen injector coils were shorting out, the hotter the motor got the worse the miss = the hotter the injector coils got the worse they performed. Hope this might help out some one else down the road.


Tom