When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Just bought a 1991 Vert. Was stumbling around under the hood and noticed a jumper wire attached to the wire that comes from the tach terminal at the distributor. Inadvertently caused the other end of this wire to become disconnected from where ever it was connected. Now car won't start. Can hear fuel pump with key on, engine turns over, but wont fire. Can anyone help? Please?
many pics just google 1991 corvette distributer wireing diagrams. I found them but do not know how to attatch.
Found those already. Problem is, I suspect this is someone's attempt to by pass something that should have been repaired. This kind of shade tree surgery wouldn't show up in those diagrams. Essentially, I'm on a fishing expedition hoping someone here might have an idea of what is going on.
Found those already. Problem is, I suspect this is someone's attempt to by pass something that should have been repaired. This kind of shade tree surgery wouldn't show up in those diagrams. Essentially, I'm on a fishing expedition hoping someone here might have an idea of what is going on.
You mentioned TACH TERMINAL but can you actually ID the terminal that the wire is terminated to? Lift the coil cover maybe and ID the wire color IF you can't ID it with-out. This car should have "coil 'n cap" I'd think still. Attached to TACH terminal a "does not run" might be difficult to explain.
my 2-cents, FWIW - there are two, 1-wire connectors on the coil/distributor - 12V and tach. the connectors are keyed, and not interchangeable, but then again, there's always murphy's law - . the tach wire (white wire) is one end of the tach filter assembly, and should be the forward most connector of the two. I would think a tach wire disconnect should have no effect on engine start - ??? double check the 12V connector/connection (aft, reddish-pink wire) -
Found those already. Problem is, I suspect this is someone's attempt to by pass something that should have been repaired. This kind of shade tree surgery wouldn't show up in those diagrams. Essentially, I'm on a fishing expedition hoping someone here might have an idea of what is going on.
The FSM says "A tach filter or tach circuit that is shorted to ground will result in a no spark condition". It can also damage the coil and ignition module.
Good luck.
my 2-cents, FWIW - there are two, 1-wire connectors on the coil/distributor - 12V and tach. the connectors are keyed, and not interchangeable, but then again, there's always murphy's law - . the tach wire (white wire) is one end of the tach filter assembly, and should be the forward most connector of the two. I would think a tach wire disconnect should have no effect on engine start - ??? double check the 12V connector/connection (aft, reddish-pink wire) -
There is a jumper wire attached to the white wire in the pic. This wire came loose from where ever it was jumped to and car hasn't started since. Any idea where it could have been attached? Could this be an attempt to bypass tach filter? If so where would the other end connect to?
There is a jumper wire attached to the white wire in the pic. This wire came loose from where ever it was jumped to and car hasn't started since. Any idea where it could have been attached? Could this be an attempt to bypass tach filter? If so where would the other end connect to?
just follow the jumper wire to see where it goes. just a stab in the dark, but the original tach filter MAY have gone bad, and the PO could have run a secondary filter, by-passing the original. he could have disconnected the original at the filter's input connection. who knows??? the other end of the tach filter plugs into one of the main harnesses.
as Pa'svette said, "A tach filter or tach circuit that is shorted to ground will result in a no spark condition" - this I did not know, but you're saying it's disconnected, and causing the no start. so disconnected, cannot be shorted. first thing, trace the circuit and see where the other end of the jumper goes. reply back - let us know. good luck -
just follow the jumper wire to see where it goes. just a stab in the dark, but the original tach filter MAY have gone bad, and the PO could have run a secondary filter, by-passing the original. he could have disconnected the original at the filter's input connection. who knows??? the other end of the tach filter plugs into one of the main harnesses.
as Pa'svette said, "A tach filter or tach circuit that is shorted to ground will result in a no spark condition" - this I did not know, but you're saying it's disconnected, and causing the no start. so disconnected, cannot be shorted. first thing, trace the circuit and see where the other end of the jumper goes. reply back - let us know. good luck -
That's the trouble, don't know where the other end of the jumper went, it's just hanging loose. Engine ran when it was plugged in, can't find where it came detached from.
That's the trouble, don't know where the other end of the jumper went, it's just hanging loose. Engine ran when it was plugged in, can't find where it came detached from.
let me see if i'm reading this right - you have a connector plugged into the tach position on the distributor. that connector has TWO wires coming off it - ??? - i'm assuming one wire is going to the tach filter, and the other wire is hanging loose - correct?
[QUOTE=Joe C;1591338584]let me see if i'm reading this right - you have a connector plugged into the tach position on the distributor. that connector has TWO wires coming off it - ??? - i'm assuming one wire is going to the tach filter, and the other wire is hanging loose - correct?[/
That's it.
Perhaps the OP doesn't realize which harness/wires he's dealing with. There's a WHITE in the distributor module harness to the ECM. OP says tach terminal but it's just next to unbelievable that it could possibly be his run issue. Just because it's a WHITE wire in the vicinity of the distributor doesn't make it tach related.
OP just needs to confirm appropriate wiring to coil etc. pi$$ on anything connected to the tach terminal and move on. OP should be able to make the car run with simple "hands on" diagnostics and repair.
Remove any wires that might be attached to the tach terminal if there is. That would avoid grounding which actually will take out the coil and the module. Has that already happened? OP needs to check and confirm.
The TACH terminal on my '84 has always had two wires to it. One to the tach filter, and the second wire just hanging loose. No idea what it's for! No place to connect it, and it's not shown in the FSM. Engine runs just fine, and tach works fine, too. Been that way on my '84 since day one. The two white wires in the TACH connector is a factory crimp! Can't believe they didn't change that by 1991!
Yea, weird!
Last edited by Hot Rod Roy; Jan 17, 2016 at 05:37 PM.
The TACH terminal on my '84 has always had two wires to it. One to the tach filter, and the second wire just hanging loose. No idea what it's for! No place to connect it, and it's not shown in the FSM. Engine runs just fine, and tach works fine, too. Been that way on my '84 for years! Can't believe they didn't change that by 1991!
FWIW, both my 85 and 90 have a single wire going to the tach connection, a single 12V wire connection, and a 4-wire connection (ECM) as shown in WVZR-1's diagram.
The TACH terminal on my '84 has always had two wires to it. One to the tach filter, and the second wire just hanging loose. No idea what it's for! No place to connect it, and it's not shown in the FSM. Engine runs just fine, and tach works fine, too. Been that way on my '84 for years! Can't believe they didn't change that by 1991!
That would avoid grounding which actually will take out the coil and the module. Has that already happened? OP needs to check and confirm.
If I read that diagram correctly, the electronic switch B pulses the white tach circuit to ground, so grounding this wire shouldn't damage anything. Of course, the tach won't work! Just don't short it to the 12 v. wire right next to it!
If I read that diagram correctly, the electronic switch B pulses the white tach circuit to ground, so grounding this wire shouldn't damage anything. Of course, the tach won't work! Just don't short it to the 12 v. wire right next to it!
I might have thought not either but your '84 will have a note that it will (the way the FSM is done it's more visible as a warning) and all others it's a little more subtle and easily overlooked. Look at 8A-17 and it calls out (121) with an *. I'm quite sure I saw it noted after seeing "PA'S" post mentioning it for other years.
Odd that it mentions that and yet there's a blunt cut just hanging like you mention and "CCRAZOR" confirms. Does the blunt cut appear in the wiring schematic at the rear of the '84 FSM?
** Poking around it seems this is debated from time to time. It is the Internet so .....
OP only needs to confirm condition of coil & module - move on.
Very basic understanding of a 7 pin HEI module and check
I just went out to the garage and unplugged the tach wire from my 91 to see if it would run with the white wire off, and it does. So the tach wire being off won't cause the no start problem unless it touched to ground and fried the coil or module.
Bob
'91 Vert won't start
. the tach wire (white wire) is one end of the tach filter assembly, and should be the forward most connector of the two. I would think a tach wire disconnect should have no effect on engine start - ??? double check the 12V connector/connection (aft, reddish-pink wire) - 
