73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Chevygold on March 27, 2024, 12:05:46 PM
-
Hope the experts on here might be able to help me out with my distributor on my truck. The truck came with this fitted and I'm now trying to get the motor to run properly. Motor is a 383 stroker TH400 tranny carb a 670 street avenger, primary seems to be OK now but haven't been for a test run yet as just finished putting it all back together following a bit of a refresh of the body.
So here's where I am now she revs good up to around 5K then strats spluttering and missing, at first thout it was the carb but the mixture was fine running in the 13-14 AFR so thought I'd take a look at the distributor, with the cap off it was clear the contacts in the cap were badly in need of a clean so they were all cleaned along with the centre button in the cap, the spring contact on the rotor and the side contact, refitted the cap and it was better but still not great so started to think maybe timing as I've never touched it. I think it's a later HEI dizzy can't see any markings other than Delco-Remy and Made in USA the top of the cap is marked LATCH at both sides of the flat area on the top which I take it is to clamp the adaptor for the diagnostic gear which I have. One thing I noticed a while back is the lack of a vacuum capsule but just assumed it was taken care of electronically? the other find was a four way lead ending in a plug which is just hanging, wire colours are Yellow, (could be white?), Pink/white, Brown/black and Black, should this be plugged in somewhere? So without a vacuum unit what do I set the timing at, abot 35 all in?
Sorry for the long post but wanted to give as much info to help, truck is a 1976 C10 longbed.
Thanks all
Graham
-
76 C10 longbed 383 stroker with TH400 tranny.
Trying to get my truck running better after a bit of body TLC, been playing with the carb to get decent combustion AFR and think it's OK on the primary now although still need to put the new carpet in and the seat before I can give it a road test!
After deciding maybe it was an ignition fault so opened up the dizzy and found the contacts in the cap in a bad way, set to with some wet n dry and got them looking good, gave the centre contact a clean as well while I was there, also cleaned the rotating contact and centre spring contact on the rotor.
Put it all back and it was better but still misfired above 5K revs so wondered if it's maybe the timing which I haven't touched since I got the truck.
Anyway the dizzy doesn't have a vacuum unit fitted which I've never really give much thought to until now so how do I time it? 35degrees all in maybe? Other than Delco-Remy and Made in USA I can't find any numbers on the dizzy, also there is a 4 way connector attached 4 wires yellow (or white?), pink/white, brown/black and black, pictures attached, should this be plugged into something which I don't have?
Thanks
Graham
-
Dizzy's are for Honda boys. Swap out a vacuum advance HEI in place of your "dizzy"
-
Hi Vile could it be the vacuum unit has just been removed for some reason? If it stops raining tomorrow I'll see what the timing is now and post what I got.
Graham
-
I'm going to guess someone swapped that in once upon a time.
-
Put the timing light on and firing at TDC at idle, which I think went to 6 degrees max when revved, that might be wrong as I left the bit of paper in the garage when it started raining again!!
Anyway set it to 35 degrees all in and it seems to run OK but still have the misfire above about 5K.
I've ordered a Moroso adjustable vacuum unit and a Proform ignition module, once they arrive I'll pull it and rebuild it with the vacuum can first and see what it's like but I suspect the module is on its way out, I always try to do just one thing at a time otherwise you never know where the fault was.
I have my Snap on analyser all ready to put on and see what that tells me but we've just had a thunderstorm with hailstones so not going out there again just yet!!
Will update once I get back to it.
Thanks
Graham
-
Quick correction on my previous, timing was TDC then 11 degrees all in at 3500 revs +, so mechanical advance is 11 degrees, does that sound about right?
When I fit the vacuum unit how many degrees should the vacuum add to the plot? Thought I'd connect my vacuum pump to the unit for setting purposes?
Thanks
Graham
-
Knew dizzy would trigger someone... 8)
You can add VW kooks to that group ::)
Is there an acceptable acronym for distributor? ;D
-
Is there an acceptable acronym for distributor? ;D
Yeah! I think it's, "distributor." ::)
-
Very funny bd ;D
How about 'dist'?
What other system uses the word except for fuel, and vaguely at that?
Oh, and the VW kooks are like the Honda boys, if there was any confusion. They Love them some 'dizzys'!
-
Just to update I now have a new cap and ignition module, vac unit on back order so once I have that I can get started but in the meantime either my ignition switch or inhibitor has gone bad as I can't get a crank, the joys!
Graham
-
Vacuum unit? Why not just get a new vacuum advance distributor?
-
Hi Vile, mainly cost, living in the UK I don't have access to such things at a reasonable cost and I'd rather stay with the original Delco Remy item rather than go with one of the Chinese copies.
Graham
-
Well what you have in there does not look like the correct distributor to begin with. Is that all you can get there is Chinese?
-
I noticed that too but thought the pic got squashed, but looking again, it looks like it's much shorter than a stock distributor.
-
No, it appears to be an ESC distributor is what I am referring to.
-
Pardon my ignorance but what is a ESC distributor? I have a new cap which is the same as the one fitted, bought it as the contacts in the cap are very badly corroded/burned, I cleaned them as best I could but they're still not great. When I put my test machine on and did the cylinder cut test results were pretty much even except cylinder 4 which didn't drop much suggesting it wasn't doing much.
Graham
-
Electronic Spark Control. ESC Distributors are to be used with an ECM, Knock Sensor, Vacuum controls and are for retarding the ignition timing if spark knock is detected. What you have is an anti-performance distributor.
You want a standard HEI vacuum advance V8 distributor.
-
Here's a couple of pictures of what I've got, no weights, 7 pin ignition control module and no provision for a vacuum unit so looks like I'm in the market for a new distributor, wish I'd pulled it sooner now! Any suggestions and any to avoid?
Thanks
Graham
-
And another
-
Graham, your earlier narrative regarding ignition timing advance increasing to 11 BTDC at 3,500 RPM caught my attention.
@ Vile:
Do you know whether an ESC distributor module has a built-in timing curve? I've never had reason to question this until now and assumed that timing was strictly dictated by external input from the ECM, modified by the ESC module. If my assumption is true, why is ignition timing advancing with no ESC module connected to the distributor? Although one might expect a worn timing chain to retard timing, I wonder if validating the timing chain condition while waiting for a replacement distributor is prudent.
-
Hi BD, it was a definate 11 degrees consistently repeatable, timing chain is quiet and timing is dead steady so I can only assume advance is made in the ICM hence the extra connections.
Been looking at replacement units and Amazon have one at a good price with good reviews, Voltstorm, also a Proform from a UK supplier I've used before but that's about a third more. Still looking but not many options, current exchange rates make buying from the USA less attractive :-(
Graham
-
So I won this MSD 8362 Distributor Street Fire on fleabay for £89 needs the ICM replaced which I happen to have so figers crossed it all goes according to plan, I could do with a stroke of good luck for a change, got a set of plugs on order as I broke 2 getting them out, the joys of headers!
Will update once it's all back together.
Graham
-
The HEI/EST is used on models with Computer Command Control (C-3) or Electronic Fuel Injection systems. The system utilizes a distributor similar to the unit used with conventional HEI systems that has been modified to allow spark advance to be controlled by the fuel control system Electronic Control Module (ECM). Modifications to the distributor include a revised ignition module, with additional terminals to receive signals from the ECM, and the elimination of the conventional centrifugal and vacuum advance mechanisms. In addition, some models use a Hall effect switch mounted above the pickup coil in the distributor to provide a reference pulse to the ECM. The ignition coil on HEI/EST systems is mounted either integral with the distributor, Fig. 1, or remotely mounted, Fig. 2, depending upon engine and application.
Primary current switching in the HEI/EST system is performed by the ignition module based on reference pulses from the pickup coil as in conventional HEI systems. However, all spark timing changes in the HEI/EST system are performed electronically by the Electronic Control Module (ECM). The ECM monitors information from various engine and vehicle sensors, determines the correct spark timing and signals the distributor to change timing as necessary. An EST bypass circuit is incorporated into the ignition module to allow ignition in case of ECM failure and to allow base timing adjustment.
On some HEI-EST systems, Electronic Spark Control (ESC) is used to retard ignition timing when detonation occurs. The ESC system consists of a knock sensor, distributor module and controller. The knock sensor is an accelerometer or magneto-strictive device, mounted on the engine block. It detects the presence and intensity of detonation by vibration characteristics of the engine. The sensor's output is an electrical signal which is sent to the controller. The controller is a hard-wired signal processor and amplifier which operates from 6 to 16 volts. The ESC controller processes the sensor signal into a command signal to the distributor to adjust spark timing. This is a continuous process monitoring and controlling detonation.
When detonation is detected the spark advance command is delayed, providing the level of retard required. The spark is retarded for 20 seconds, then the spark control returns to EST. The amount of retard is determined by the controller based on the severity of detonation. A failure of the sensor would allow no retard, while controller failure would be indicated by no ignition, no retard or full retard.
-
Make sure you ohm the pickup coil before replacing the module.
-
Ran the following tests on the existing unit and everything tested good pick up was 500 ohms and infinity to ground on both wires, BAT to TAC gave 0.5 ohms and infinity to ground so coil looks good so while I'm waiting for the MSD I'm putting it all back as was just in case I need to move the truck. Will check everything over on the MSD when I get it, all I'm waiting for now is a set of plugs and a selection of plug sockets to deal with the awkward one!
Graham
-
MSD arrived and so far having gone through it from top to bottom I can't find anything wrong with it, only thing I did find was that the centre contact under the coil was wrongly assembled, the brass collar was above the rubber insulator so it didn't protrude down from the underside of the cap to make contact with the rotor!
Coil checked out resistance wise, put a test lamp on the ICM and it pulsed like it should as I turned the shaft, pickup checked out good, still waiting for plugs to arrive so have fitted the MSD so once I get the plugs we'll see if it runs!
Graham
-
Just remembered where should I stop off the vacuum advance and what effect would more or less have?
Graham
-
https://static.summitracing.com/global/images/instructions/msd-8362.pdf
-
Hi Vile thanks for the link but I'd already found that info, anyway after a false start when no start as no spark even though all the tests I'd done checked out so changed the ICM for the new one I already had and bingo the beast lives! So my MSD cost me about £140 to get me going again, motor revs cleanly to 6K without any hint of the misfire which was there before, ran out of time today so didn't get time to check the timing at full advance and with the vacuum connected so will update tomorrow.
Many thanks for all your help
Graham
-
Fired up the truck on the old home made Chinese plug leads and all was good so then I decided I'd fit the Accel leads that came with the MSD and now my tacho is dancing all over where with the old leads it was steady, seems to steady up once the revs get up a bit but at idle it's crazy!
Graham
-
Replace the old leads one at a time with the Accel leads. When it starts acting up - you will know which is bad. Could just be a bad crimp!
-
Sounds like your tacho is dizzy 8)
-
Dem little green leaves in dem dizzy tachos aint cilantro, my friend!! WooHoo!!! ;D
-
It's got me that dizzy I've gone back to getting the interior back together, could do with some of that herbal mixture to cure my headache!
Graham
-
Think I'll put my diagnostic rig on and see what the traces look like on the screen for each cylinder.
Graham
-
Double check the firing order. Make sure you didn't cross 5&7
-
Pretty sure FO is good, I checked double checked and then checked again just to be sure but will look again, one thing I noticed was all was good at first start but after running for 5-10 minutes the dancing tacho started again, above 2500 it's steady again then back to idle and back to its tricks again.
Graham