One last shot... Breaking up!

[BoostedSUV]

Re: One last shot... Breaking up!

I'm going to take it a shop this week where Nick (NJ93TY) works. One of his mechanics is going to look at some things. I will ask if they can check the emissions from the tailpipe...

 

[thunderace31]

Re: One last shot... Breaking up!

I had a 91 Z28 drive me nuts one time with about the same issues. I replaced just about every thing you have. module-pick-up, ecm, inj, What it turned out to be was the tach board in the cluster was shorting outing the signal at the coil somehow. if it's possible try and unhook the tach wire to see.


I'm still thinking about your nightmare and what else it couldn't be!

Ahhh I bet this could be it! I had an Autometer tach go bad on me and It did the same thing!
I bet this could be the issue a loose wire or bad board Something I never thought of!
Worth a try :tup:
I still feel bad about your truck and your situation Id have done gave up by now :rant:

 

[BoostedSUV]

Re: One last shot... Breaking up!

Anybody have any ideas on how to check if it's a tach signal issue? I can probably cut the tach wire off the back of the dizzy but I really don't want hack up my engine harness and the ECM still needs to see engine RPM.

 

[cloneman315]

Re: One last shot... Breaking up!

unplug the dash?

 

[BoostedSUV]

Re: One last shot... Breaking up!

I'm going to pull out my schematics and trace the tach signal wire. Maybe I can make it just feed the ECM and see what happens.

What do you guys thing about just letting the MSD supply the tach signal instead?

 

[thunderace31]

Re: One last shot... Breaking up!

I'm going to pull out my schematics and trace the tach signal wire. Maybe I can make it just feed the ECM and see what happens.

What do you guys thing about just letting the MSD supply the tach signal instead?

Id say disconnect it from the back of the tach at the dash connection

 

[SloGN]

Re: One last shot... Breaking up!

The Ecm gets its tach signal; from the module. The dash should get it's signal from the white wire on the sam plug as the 12v power.


You can try and make a jumper to unplug that plug and just feed the coil with 12v via the jumper wire.



The rpm signal to the ecm is gerated thru the est wire i believe

 

[BoostedSUV]

Re: One last shot... Breaking up!

The Ecm gets its tach signal; from the module. The dash should get it's signal from the white wire on the sam plug as the 12v power.


You can try and make a jumper to unplug that plug and just feed the coil with 12v via the jumper wire.



The rpm signal to the ecm is gerated thru the est wire i believe

Anybody know if that hareness was different from a 92 to a 93? I have a 93 dash harness/fuse box in my 92 and there were a few things different and I had to relocate a couple terninals in the fuse box. Maybe I missed one and that's causing my issue?

 

[turboj91]

Re: One last shot... Breaking up!

So how would this relate to the problem. The signal is the signal. It doesn't break up until it gets up to operating temp. The warmer the temp the worse the problem. How does the signal relate to this. Changing injectors moved the problem up the rpm scale. Again, how does the signal relate. I will assume nothing else was changed or touched besides the injectors (and the tune). Granted, the 6K+ rpm reading while cranking is wrong but the puzzle pieces just don't fit.

 

[SloGN]

Re: One last shot... Breaking up!

Any updates?

 

[SloGN]

Re: One last shot... Breaking up!

So how would this relate to the problem. The signal is the signal. It doesn't break up until it gets up to operating temp. The warmer the temp the worse the problem. How does the signal relate to this. Changing injectors moved the problem up the rpm scale. Again, how does the signal relate. I will assume nothing else was changed or touched besides the injectors (and the tune). Granted, the 6K+ rpm reading while cranking is wrong but the puzzle pieces just don't fit.

Well a bad connection gets worse with heat. so if the tach and siganl wire is bad that could be the source of the problem. 6k rpm when cranking yeah it has a problem. that the clue.

do these trucks have a rpm signal buffer before it gets to the ecm?

I wonder if he is having a timing issues as well. may be he can unplug the est wire and manually set the timing @ 15 degrees advanced then try and drive the truck. doing that will bypass the ecm's ability to control the timing. for all we know the est module could be bad and still not set a code 42.



I'm still pondering on this issues but me being here in nc and not laying eyes on the issue i can't really help out much.

 

[Quickstop [UK]]

Re: One last shot... Breaking up!

Is there a DM file of this phenomenon? We would see the RPM go nuts at the speed mentioned and maybe the other factors would show up the problem?

 

[WyoSyclone]

Re: One last shot... Breaking up!

Well a bad connection gets worse with heat. so if the tach and siganl wire is bad that could be the source of the problem. 6k rpm when cranking yeah it has a problem. that the clue.

do these trucks have a rpm signal buffer before it gets to the ecm?

I wonder if he is having a timing issues as well. may be he can unplug the est wire and manually set the timing @ 15 degrees advanced then try and drive the truck. doing that will bypass the ecm's ability to control the timing. for all we know the est module could be bad and still not set a code 42.



I'm still pondering on this issues but me being here in nc and not laying eyes on the issue i can't really help out much.

Yup, I'm still thinking wiring too... that 6k when cranking is a clue. The timing test would be a good one.

 

[BoostedSUV]

Re: One last shot... Breaking up!

Any updates?

I put the right knock sensor in and the code 43 went away. I purchased another engine harness to put in and after that I'm done...

One thing I noticed is when the truck is sitting stationary and I bring the RPMs up to around 4k the speedo shows 4-5 mph. It starts to climb up after 3500. Could be normal or a clue?

 

[SloGN]

Re: One last shot... Breaking up!

I put the right knock sensor in and the code 43 went away. I purchased another engine harness to put in and after that I'm done...

One thing I noticed is when the truck is sitting stationary and I bring the RPMs up to around 4k the speedo shows 4-5 mph. It starts to climb up after 3500. Could be normal or a clue?

I don't think it should do that. I'm wondering if you ought to pull the gauge fuse and try and drive it.

Have you tried to unhook the white wire on the coil. the white wire i talking about is located in the same plug as the 12v power wire on the coil. this is the tach feed for the dash.

 

[BoostedSUV]

Re: One last shot... Breaking up!

Pat I didn't try that yet. I will unplug that connector and run a jumper for power. I did notice that on that particular engine/dash connector that the ltgreen and drk green wires are reversed but it shows that being correct on the schemetics...very weird

 

[SloGN]

Re: One last shot... Breaking up!

pat i didn't try that yet. I will unplug that connector and run a jumper for power. I did notice that on that particular engine/dash connector that the ltgreen and drk green wires are reversed but it shows that being correct on the schemetics...very weird

crickets.......................................................

 

[sly dvl]

Re: One last shot... Breaking up!

One thing I noticed is when the truck is sitting stationary and I bring the RPMs up to around 4k the speedo shows 4-5 mph. It starts to climb up after 3500. Could be normal or a clue?

I've seen this before with elec. speedo's. Make sure your ign. wires are NOT running parallel to any other wires under the hood. They can induce voltage into a low level signal wire, like the VSS. It's possible that there's some induction going on creating interference with other low level signals. Although, I doubt this is your driveability problem since it's very RPM specific. But, could be your phantom speedo reading...

 

[BoostedSUV]

Re: One last shot... Breaking up!

The plug wires are run in same manner as the factory ones were. Interference is a possibility but the go perpendicular with most of the wire harness. Its has also done this with 2 sets of wires so its not a bad wire being the problem...

I'm just waiting for a decent day to swap engine harness' and see what happens. Its just been to damn cold here in NJ!

 

[SloGN]

Re: One last shot... Breaking up!

The plug wires are run in same manner as the factory ones were. Interference is a possibility but the go perpendicular with most of the wire harness. Its has also done this with 2 sets of wires so its not a bad wire being the problem...

I'm just waiting for a decent day to swap engine harness' and see what happens. Its just been to damn cold here in NJ!

Have you tried unhooking the tech lead yet? like i mentioned earlier.