Earendil

Hi,


there are some similar thread around, but..


I am experiencing loss of power at 6th gear. Put it on 6th at 60-70 mpg and I even start losing speed.. as if the car is clogged..


So should be either fuel pressure or clogged cat., right? .. there's also the spark plugs, cables, cap, etc.., but should I just start changing everything.. seem s a bit costly way of diagnostics..


Today it even threw "chech engine" light, but when I try to see codes, there is error in communication with ECM, so cannot see the codes in group 4. (wondering how to fix that either).


I would not trust local garrages as they look at the car as if it is some kind of spaceship..(well , it is a very rare machine here) and are generally quite reluctant to read..


Some advice would be very helpful.. where to start from..

bogus

Year? It's at least a 1990, it has a CCM...

Did you get a SYS light on the Speedometer?

The loss of comm is bad, that means the ECM is no longer talking to the CCM, at which point, the car should not start.

You see, the VATS - that little chip on the key - is read by the CCM, and it sends an OK or Not OK to the ECM. If it gets nothing, the car won't start.

There is no repairing of the ECM. You have to source a good used one, if your vette is a 92 or 93, the 93 Firebird or Camaro with V8, will work perfectly, just swap the chip.

As for lugging in 6th, I would be suspect of fuel pressure. Check filter and such.

Tom400CFI

Bogging in 6th, I'd test fuel proessuer, *** suggested, and check for excessive back pressure (clogged cats).

For ECM communication issues, I'd PM "Hooked on Vettes" here on this forum...he is the MAN for diagnosing that sort of issue.

Earendil

Interestingly though, the car is starting just fine. As I said, it is returning H codes form module 1 (CCM?) and 9. but in group 4 (ECM?) it shows only "Err".

I will check fuel pressure as a first.. thx for the input.

Tom400CFI

"H" is history. Not current code.

Mine shows "Err" in group 4 also.

DanielRicany

Better yet, plug a scan tool into and drive at 60-70 MPH in 6th gear. See what the BLMs look like and that will tell you if it's running towards the rich side or the lean side based on factory calibration.

Earendil

OK, that's a ODB1 scanntool, correct? I have such for ODBII for my other vehicles.
Will I be able to read the ECM data with such a tool since it's not communicating with the Digital display?

DanielRicany

If it is a 96 the OBD II will work, if not you will need a special connector with an OBD I scanner. An OBD II connector that reads OBD I systems. I think they started the special connector thing in like '94. If you don't have one already then just start off with what the others are suggesting.

jimmers

I thought you could get them remanufactured?

Tom400CFI

You can.

jimmers

That's what I thought. Was freaking out a bit there. Thought something changed and I'd have to find a backup just in case!

Earendil

Ok, it's worse now. .. now the problem is in all rpm range. Different than I described before.


The idle is a bit rough.. it has like "hick-ups".. I experience power loss in all gears.. to an extend that car car was undrivable yesterday and even cut off a few time.
Put it on higher gear.. it stalls.. try lower gear-high rpm.. same thing.. fells lige totally clogged.. and all of a sudden like it "uncloggs" with a strong kick felling like it will brake the halfshafts... and takes off..


Maybe it is a combination of problems, because I think weak pump shold stil supply ok fuel fopr idle? It is a PIA I cannot read the ECM codes..


I have checked the spark plugs yesterday. The gaps on most was around 0.9.. so I took them down to 0.5 .. no change at all.


The vacuums outside the plenum checks out OK.

Maybe it is time to take off the plenum since there is not much I can access with it on.


(I might not be using the right words/terms since I am not native engl. speaker).

-=Jeff=-

What Year?
How many miles? (Curious for the catalytic)
Have you checked Fuel pressure yet?

jimmers

Check the fuel pressure at idle and as you're driving.

Tom400CFI

Also.

Also, what is your tach needle doing when the car is acting up? Does it seem like it shows the actual RPM accurately? Or is it pretty wildly fluctuating?

Earendil

OK, just got a nice pressure measuring kit today and gave it a go.
The readings are somewhat inconsistent.


Try at cold edgine:
1. Key is ON, pressure would go up to 52 for a sec and then hold to 45 psi.
2. Idle rpm (about 1000) playing up a bit (tacho needle playing just a bit along). Pressure holding at 43 psi.
3. Unplug vacuum from regulator - psi up to 52.
4. revv a bit - psi moving accordingly. Revv steady at 2500 rpm - 42 psi


Then I took it for a short spin.. it managed to cut off completely at 100 mph (then I shifted from 4th to a neautral).. lost steering.. but started it fast and went on.. same problems. Sometimes it would not take off from low rpm from 3rd or 4th.. or even 2nd..


Did a second measure..


This time with key on it took it only to 40 psi and held there.. otherwise all the same. tried a couple of time key on and off.. still just to 40 psi (maybe because the car was warm now?).


I did notice however that with eninge off within a few minutes the pressure would climb very slowly up all the way to 50 psi? Is this normal?


Now I now it would be helpful to have the pressure gauge taped on the windshield, but the hose is a bit short and on the LT5 the valve is to the front of the engine.. not next to the windshield.. I have to lenghten the hose somehow it somehow..

Short video: https://www.dropbox.com/s/asc7e2hft2...10.42.mp4?dl=0


From 1.45 in the video on you can see as it slowly starts to pick up pressure with engine off.

Earendil

less than 60k miles. 93' 40th aniv. LT5


Would the catalytic mess also at low speed? Say doing 20-30 mpg and tryig to take off from 3rd gear for example..

-=Jeff=-

LT5???

Key on? (not ignition)

any SES light?

Have you replaced the injectors? the OEM ones from some of years cannot handle the ethanol and start to leak.. being at 43 cold then 40 hot has me wondering if there are some leaky injectors.. does it run fine cold but act up as it warms up?

Earendil

Well.. as I've said.. I am not native english speaker, so I might not use thre proper wors.


LT5 - should be the engine.
Key on = ignition on (that's what ment)
SES lights - no, but then again, I cannot pull out the errors from grup 4. A couple of times it did lit up "check engine" but couold not see codes afterwards..




It does seem better when colder and gets worse and worse the longer i drive it.. not 100% positive though.. last time I made it home on 2nd.. end today cut off at 100.. I am a bit hesitant to take it for a longer drive..

-=Jeff=-

Yes I wanted to confirm it was an LT5.. the LT5 has a second key in the console for full power, I assume that is 'on'

if the SES (Service Engine Soon/ Check Engine) came on and you lost power it could be Code 61, port throttle error..

what are all the codes you have been able to retrieve?

EDIT.. post on code 61 for LT5

http://zr1.net/forum/showthread.php?t=14932