Weird timing issue...

Just my 2 cents worth but...............

I recall the jumping of wires to eliminate the esc module, I cant remember the specifics of it but if it is what you say it is , just an input and and output then the pick up is waiting on an input from the knock sensor thru the module? basically an electrical/electronic signal? what if all you did by jumping the wires is send a signal to the pick up to retard the timing due to the signals coming into the input connector?

I am going to look for the bulletin and info on this mod.

Reply to
The Jones'
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i skipped through some of the posts..lots to read...i don't know if anyone mentioned this and i don't know if it's relevant...i came across a similar situation a few times on 88-94 chevys...HUNTING timing..timing moves all over...some times runs ok till your on the gas, some times idles bad...the rector wheel with the magnets on it,on the distributor shaft was loose, and spinning on the shaft...sometimes they can move at idle and sometimes they need instantaneous acceleration, like you revving it up, to move. unfortunately there is no fix for this, you have to replace the distributor assembly...i've seen this about 1/2 a dozen times...its not that commen

let me know what happens.

redeye.racing

Reply to
redeye-racing

Well...I have (what I call) a "2nd Generation" HEI. Whether it's truly the 2nd version of the HEI, I'm not sure, but it's the 2nd version I'm aware of.

This one is *supposed* to use a 5-pin module. It has 2 pins on one side for the condensor to connect to, but the other end has 3 pins, rather than just a G and W. That end connects to both the pickup coil as well as the external ESC/ECM. The connection that comes from the pickup coil has 3 pins of course, only 2 of which go to the coil. It has both female and males ends, and functions as a "pass-through" connection (that's what I call it). This basically just allows the ESC connection to piggyback onto the module after the pickup coil is connected.

If I hadn't messed with that connection, we wouldn't be having this conversation. I had figured that a 4-pin (1st generation...no ESC) module would work just fine in this distributor, despite the fact that the pickup coil connection was different. But because of the spacing of the pins in that connector, it wouldn't work. So I used the smallest flat-head precision screwdriver I had, and pushed the metal tabs down to slide the metal pins and wires out of the connector housing without damaging them or the housing.

I blew out my 4-pin module, as well as two 5-pin modules, because I didn't have the internal ground wire connected to the ignition coil. I thought when I reassembled that connector (to try out the 5-pin modules) that I reassembled it correctly. I apparently did NOT :-)

As it is, the ESC is disconnected, and although I'm using a 5-pin module, it functions as the earlier, 4-pin version of the HEI. I ended up using the ESC connector that piggybacks onto the pickup coil connection and removing the center wire, then ran a short wire between pins 1 and 3. That way there's no external harness coming out the back of the distributor. I could've used female blade connectors and accomplished the same thing. In fact, that's what I plan on doing when I document the process for others to see.

I have a spare HEI of the same vintage as mine, so I'm going to be taking some pics of the whole modification procedure to post on my site for others to see.

~jp

Reply to
Jon R. Pickens

Feel free to post a article about it on my site/forum to if you want too. I will remember this one too as I had never seen if before either (as I mentioned earlier). On a side note, unless you have a large overlap/aftermarket cam, the vacum sounds a bit low at a idle (from what you stated) .

----------------- The SnoMan

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Reply to
SnoMan

I hadn't realized that you had modified the harness to the ignition module, I was under the impression that someone had sent you the distributor wiring that burned up in the fire and that all you had done was jumper the 4 pin ESC connector to by-pass the knock control. I'm very familiar with the by-pass modification, was doing them

20 years ago in the dealership. Fastest way was to pull the glove box down and cut the green and black wires and splice them together. Neat, clean and protected from the elements. Of course, this assumes everything forward is in tact.

I should have had you send me some pictures of the open distributor, things would have progressed much faster.

Anyway, it's fixed and now you can move on to the transmission leak. That rates an atta boy!

Reply to
aarcuda69062

The pick up receives no signals, it outputs an AC voltage to the ESC box under the dashboard, the ESC buffers the signal from the pick up and sends it back out to the ignition module, when the ESC box receives a knock signal from the knock sensor, it modifies the buffered signal, retarding the timing.

By having the pick up wires reverse polarity, he altered the shape of the AC signal from this; /I /I /I /I / I / I / I / I / I/ I/ I/ I/

To this; I\ I\ I\ I\ I I \ I \ I \ I \ I I \I \I \I \I

Since the module triggers on the falling edge of the pick up signal, as RPM increased, the peak to peak voltages went up and as they did, the trigger point retarded.

Good lesson on reactance and reluctance... (apologies if my ASCI art doesn't turn out.)

Reply to
aarcuda69062

Well, the cam is stock to the engine, but as I stated earlier, the engine (290hp) is the same as the 260hp motor, with the exception of the cam.

Here's the cam specs: ".450'' intake and .460'' exhaust lift", and "Flat Tappet Duration @ 0.050'': 222=B0 I, 222=B0"....per the Jegs site.

I was never able to get a lot of vacuum on this engine. With everything plugged, and the timing and idle circuit set to max vacuum, I was able to get 16" Hg once, but that was only because I was trying to achieve max vacuum, not because it ran best that way.

What's sad is, after all this, I can now tell that the engine is running rich as ever, at least at idle. No idea how the smaller jets will affect the cruise and power mixtures yet.

I'm about to throw this carb off a cliff and get another Quadrajet... Eh, I won't do that. But the TBI swap is looking *mighty* good.

I'll post the info on your site once I've got photos taken. May not be this week, as I got packing and moving to do, but next week at the latest probably.

~jp

Reply to
Jon R. Pickens

I wasn't able to locate one. I found the big connector going to the firewall at Pep Boys and the internal connector that went to the module was ok, so I made a new one from scratch. I never was able to make it run, but again, when I was using that harness I still didn't have the ground wire connected to the coil, so it was futile.

Yeah, I know it could be done pretty much anywhere... I just chose to do it internal to the distributor and eliminate the harness out of the distributor altogether. Looks cleaner. I do plan a TBI swap at some point, preferably sooner than later. The Edelbrock carb just runs way too rich and I'm sick of screwing with it. It makes NO sense, but I'm almost to the point of giving up.

The big grommett on the firewall that went to the ESC will eventually be used to run to the ECM once I do the TBI swap.

Yeah, probably... I was running myself in circles. The missing ground wire caused me to kill 3 ignition modules before I caught it. By that point I wasn't even thinking about the polarity of the pickup coil wires.

Yep...calling Mr. Transmission before lunch to talk to the mechanic and set up the deal. If everything goes as planned, I'm gonna get it towed out there today, and it'll be rebuilt by Friday.

Then I can start chasing down TBI parts and gear up for more work .

~jp

Reply to
Jon R. Pickens

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Yea, been there.

I advise everyone with the 88-95 V8 chevys to dump that distrib and get the "Ready to Run" MSD distributor instead. More than worth it.

MSD-8366 Chevrolet/GMC: 1987-93 cars and 1987-95 trucks

HDS

Reply to
HDS

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