I/P values too high ... need help here
Thread Starter
6th Gear
Joined: Jan 2005
Posts: 6
Likes: 0
I/P values too high ... need help here
Hi,
After reading through the last 25 pages of this section and not finding anything about my issue with my '91 TPI (the very last probably), I dare ask for some massive help!
I've been driving my Corvette for 5 years now and for the first time I am encountering a problem that I can't solve and which isn't described in the service manual.
Symptom: I get a readout from the tachometer of around 1800 rpm at cold idle, 1400 rpm when warm. Knowing the sound it makes at 2000 rpm quite well, at that sound the tachometer indicates about 4000 rpm. And that isn't all... During a kickdown, the rpm's go way beyond the red mark on the meter. The same goes for the oilpressure gauge.
Now the rpm's are limited on the Corvette, so the readout must be false. Now the question: what's wrong and how do I fix it?
P.
After reading through the last 25 pages of this section and not finding anything about my issue with my '91 TPI (the very last probably), I dare ask for some massive help!
I've been driving my Corvette for 5 years now and for the first time I am encountering a problem that I can't solve and which isn't described in the service manual.
Symptom: I get a readout from the tachometer of around 1800 rpm at cold idle, 1400 rpm when warm. Knowing the sound it makes at 2000 rpm quite well, at that sound the tachometer indicates about 4000 rpm. And that isn't all... During a kickdown, the rpm's go way beyond the red mark on the meter. The same goes for the oilpressure gauge.
Now the rpm's are limited on the Corvette, so the readout must be false. Now the question: what's wrong and how do I fix it?
P.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by smacko
Check TVS cable adjustment
This sounds like it's time for a scan tool. if you hook up the tool to the ALDL, it will give you the information right from the CCM.
If the data matches, then you have a problem... It would lead me to believe the CCM is bad, or, the CCM ground is bad.
Does the word "SYS" flash on the speedo?
Le Mans Master
Joined: Jun 2002
Posts: 6,097
Likes: 0
From: High Plains Drifter Fayetteville, AR
Originally Posted by pieter
Hi,
Now the rpm's are limited on the Corvette, so the readout must be false. Now the question: what's wrong and how do I fix it?
P.
Now the rpm's are limited on the Corvette, so the readout must be false. Now the question: what's wrong and how do I fix it?
P.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
I don't think this is an ECM related failure.
The computer system in the 90-96 C4 is a little different... well, compared to then it is, but common now.
It uses a CCM - Central Control Module - to handle all communications between the ECM and the EBCM (ABS and then later, the ASR). The CCM is the source of all data on the IP.
This is why the first diag that needs to be done is to plug in the scan tool and read it's data. Compare it to the IP data.
I guess it is possible that the IP has fried.
The computer system in the 90-96 C4 is a little different... well, compared to then it is, but common now.
It uses a CCM - Central Control Module - to handle all communications between the ECM and the EBCM (ABS and then later, the ASR). The CCM is the source of all data on the IP.
This is why the first diag that needs to be done is to plug in the scan tool and read it's data. Compare it to the IP data.
I guess it is possible that the IP has fried.
Thread Starter
6th Gear
Joined: Jan 2005
Posts: 6
Likes: 0
Wow, that's a lot of info, thanx guys!
According to the service manual, the CCM controls all responses of the IP except for some analog gauges. My LED display is fine and so are all the light-indicators, so I don't think the IP died completely. Oil pressure also seems to be about 20% off (too high) by the way.
For the CCM, this also controls the lighting of the IP corrected by ambient light with which I sometimes have problems, I had a SYS error about one year ago that disappeared soon enough, which could very well be a bad ground. If the tach filter uses the same ground as the CCM this could explain something...
A bad ground could very well be the problem, since I had almost all of them, except for some of the hard to reach ones. It solved about 90% of all trouble I had after I bought her. How do I get to the tach-filter ground?
If it is the bolt I think is mentioned (under/behind engine block, driver's side), I fixed it already. Could it also be one of the two I didn't fix already: the IP grounds? Any easy way to get to these grounds of the IP without demolishing 80% of my interior?
P.
According to the service manual, the CCM controls all responses of the IP except for some analog gauges. My LED display is fine and so are all the light-indicators, so I don't think the IP died completely. Oil pressure also seems to be about 20% off (too high) by the way.
For the CCM, this also controls the lighting of the IP corrected by ambient light with which I sometimes have problems, I had a SYS error about one year ago that disappeared soon enough, which could very well be a bad ground. If the tach filter uses the same ground as the CCM this could explain something...
A bad ground could very well be the problem, since I had almost all of them, except for some of the hard to reach ones. It solved about 90% of all trouble I had after I bought her. How do I get to the tach-filter ground?
If it is the bolt I think is mentioned (under/behind engine block, driver's side), I fixed it already. Could it also be one of the two I didn't fix already: the IP grounds? Any easy way to get to these grounds of the IP without demolishing 80% of my interior?
P.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
I think both grounds for the IP and CCM are on the inner kickpanels.
The tach filter is a little black cylinder thingy just off the distributor.
The tach filter is a little black cylinder thingy just off the distributor.
Last edited by bogus; Jan 16, 2005 at 03:32 PM.
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Racer
Joined: Jan 2005
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From: tomahawk wisconsin
Originally Posted by bogus
I think both grounds for the IP and CCM are on the inner kickpanels.
The tach filter is a little black cylinder thingy just off the distributor.
The tach filter is a little black cylinder thingy just off the distributor.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
And the tach filter is located in a clamp which fastens to the upper rear of the engine to the left of the dist.
Follow the wire from the front left of the dist to the filter.
Follow the wire from the front left of the dist to the filter.
Thread Starter
6th Gear
Joined: Jan 2005
Posts: 6
Likes: 0
Tiny update about this problem...
The CCM is connected to the two grounds left and right behind the kickpanels. I just had those kickpannels off than it started raining AGAIN! I think where you guys live is where God works, where I live is where he pees...
G109, a ground below the engine block is one I did before, which grounds the oil level check for the CCM. So the false indicator I get must be because of bad grounds in G201 and G202 (the IP grounds also for the CCM). But this doesn't fix the tach-problem.
The only thing left is G108, which is the ground for the tach filter. If this doesn't work, the tach filter is gone and I'll replace it. As usual with a lot of Corvette parts, I probably need a guy with 1.5 inch thick flexible arms and the power to see through metal to do this. Anyone live near Area 51 that could send me one?
P.
The CCM is connected to the two grounds left and right behind the kickpanels. I just had those kickpannels off than it started raining AGAIN! I think where you guys live is where God works, where I live is where he pees...
G109, a ground below the engine block is one I did before, which grounds the oil level check for the CCM. So the false indicator I get must be because of bad grounds in G201 and G202 (the IP grounds also for the CCM). But this doesn't fix the tach-problem.
The only thing left is G108, which is the ground for the tach filter. If this doesn't work, the tach filter is gone and I'll replace it. As usual with a lot of Corvette parts, I probably need a guy with 1.5 inch thick flexible arms and the power to see through metal to do this. Anyone live near Area 51 that could send me one?
P.
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
I have a 91 and my tach is off ~200~300 rpm.
(I scan mime frequently so I know it doesn't agree with the scan data.)
Not bad as yours but it still bugeths me.
If the tach filter fixes your I may change mine.
RE The Tach Filter
Is that justa capacitor to ground similar to the condensor in a point distributor system?
If so anybody know the capacitance value?
(I scan mime frequently so I know it doesn't agree with the scan data.)
Not bad as yours but it still bugeths me.
If the tach filter fixes your I may change mine.
RE The Tach Filter
Is that justa capacitor to ground similar to the condensor in a point distributor system?
If so anybody know the capacitance value?
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by VetNutJim
I have a 91 and my tach is off ~200~300 rpm.
(I scan mime frequently so I know it doesn't agree with the scan data.)
Not bad as yours but it still bugeths me.
If the tach filter fixes your I may change mine.
RE The Tach Filter
Is that justa capacitor to ground similar to the condensor in a point distributor system?
If so anybody know the capacitance value?
(I scan mime frequently so I know it doesn't agree with the scan data.)
Not bad as yours but it still bugeths me.
If the tach filter fixes your I may change mine.
RE The Tach Filter
Is that justa capacitor to ground similar to the condensor in a point distributor system?
If so anybody know the capacitance value?