Mismatched 1988 V10 Mismatched Suburban

[MuddiGGEr25]

For specifics on the issue at hand read the last few posts by me on this forum to get caught up on what i have and have not tried.

http://www.chevytalk.org/fusionbb/showtopic.php?fid/78/tid/332480/pid/2616292/post/last/#LAST


UPDATE:

I tried leaving the EST wire connected and i disconnecting everything, and by everything I mean EVERYTHING, CTS, TPS, AIC, Spark Control, EGR, the random relays on the firewall, the Alternator, o2 sensor,Knock sensor, anything I could find with a plug except the starter, ign coil, and dist hook ups.  even with all that disconnected still backfire blowing fuel out the TBI, bang bang the usual making the neighbors open thier blinds, etc.

I disconnected the EST wire, with all that still unplugged and lo behold it starts, kinda like shoot but ran nonetheless, and could drive it, barely but better than not starting at all.

I thought perhaps my ICM was burnt up or failed, so i grabbed the 048 module i kept in the toolbox just in case, and spent an hour fiddling in the dark and snow to swap it out, the 369 module did not seem hot or burnt or any discolorment, or any smell of burnt electronics, however i swapped it anyway.

This did not solve the problem, albeit the backfire is not nearly as forceful with the 048 and i think that is due to less advance built in.

I tried turning the dizzy back to retard the timing, but it just cranked and cranked and cranked no roar, and if i advanced it past the "original spot" then it backfired faster/harder.

Like i said my timing light is non functional however i will have access to a working one on monday. as well as a scan tool with live data.

My temporary solution was to leave the EST wire unplugged, and advance the timing to the point of starter kickback, then retard it just a hair so it fires up pretty quick.

The current results are I have idle, part throttle and fast "blip" response, I have been unable to test WOT since all the local roads are covered in ice or snow, however earlier I was able to easily rev to 3000-4000 so im 95% sure its not a mechanical issue.  It seems like its still trying to retard the timing when im "maintaining" speed, but is just fine when accelerating. I got up to 45mph and held it for about a mile north bound then about a mile and a half southbound. no noticeable hesitation. the engine temp guage was reading about 130-150 since its pretty cold out and my rad is oversized in the first place.


I guess I have a few questions for anyone with some experience

#1 Could a failing ignition coil be causing this? or contributing to it? I can reach high rev's and its not misfiring so thats why I am faily sure the coil is ok, and when it was running I had a firm grip on one wire and it nailed me pretty hard, i have felt weak coils inthe past nail me, and this was not weak.


#2 is it possible that 3 ICM' modules could all be faulty? 2 were pulled from TBI's that drove into the junkard running perfectly, just had body or frame damage from an accident, and my original was replaced because i thought it was causing this issue.

#3 what could possibly be affected by water/mud splashing up from underneath? i do not have all the guards in place but there isnt a lot of water/mud stain anywhere on the engine after i got out of there.

#4 it was idling ok when i pulled into my wife's workplace but it was still stumbling under "cruise" throttle, so i reached in and checked to make sure the dist cap was snug, the truck was still running and the cap was NOT snug somehow i never got the back screw in -.- and when i tugged on it, then there was a visible spark, a bang, followed by the above symptoms, however considering the issue was gradually getting worse i think this was inevitable i just think i gave it a kick in the ass to the "fatal" stage

#5 will it still enter closed loop and use the o2 and knock sensor even with the EST disconnected?


#6 Can i disconnect the 4 pin connector on the ICM and just leave the 2 wire connector setup for the coil? Would it run like this? Where do those 4 wires go to anyway? is it possible that its in there somewhere i shorted or ripped something?



I will attempt a WOT up to redline (6000) or atleast peak TQ at 3,900 to ensure its not a mechanical issue.


When the EST wire is connected and I try to fire it up BEFORE i adjusted the dist, there would be a nice spray of fuel into the air sometimes accompanied by flames when it went bang,


When the EST wire is connected AFTER i adjusted the dist for my current workaround, it starts and runs but BARELY, like it wants to stall but its not letting itself, and if i powerbrake it lightly it backfires ever so gently.


My reasoning is that the pickup coil/stator must be sending the signal otherwise it would not run so smooth through the RPM's with the EST disconnected.

[MuddiGGEr25]

Well its gradually getting worse and blew out one of my mufflers    so now i have a deep glasspack on instead 

Anyway im 99% sure its my stator losing magnetism since I left the EST connector unhooked then advanced my base timing so its driveable but it still backfires and misses some times, and I already replaced the cap,rotor, wires, plugs, and tried 3 different ICM's that were all working the last time they were used.  And it barely has enough magnetism to pull a screwdriver or bolt to it.

I grabbed this dizzy from work from the spare/test parts bin. 99% of the time we dont keep anything unless it was working fine and the customer instructed us to change it anyway or if we part out an engine before trashing the car/truck.

I just wanted to ask if this looks correct for a 1987 5.7L TBI block.

I wil be attempting to install it regardless in about an hour just wanted to ask.

[MuddiGGEr25]

another pic

[MuddiGGEr25]

Well I installed it, its about 15 degrees clockwise from where the "old" one came out but it runs and drives alittle, I will be going to make a grub run here shortly then ill punch it and see how its doing. I found out once i got the old dist out that the "points" were colliding with the other set and i could barely get it to turn by hand, and the one i put in is a slightly different design but i put my OEM GM 369 module in the replacement dizzy to replace the 048 one.  I will have to stop and redo the timing tomorrow at the shop with a light, but ill know here in a few if it resolved the issues. I was able to reconnect the o2, knock, and EST wires and it starts, idles, revs and will power brake to 1400RPm fine, but does miss a little as the rpm's come down. setting base timing should resolve that though.


One question I do have is, since the dizzy slid down in at a slightly diffent angle than it came out will that offset my timing mark?

[MuddiGGEr25]

Ok so heres the deal, i just got back, i couldnt get it over 3000rpm trying to rev louder than a friend of mine, or over 3000rpm, when i punched it, I tried turning the dizzy both ways to do the "old school" basic timing, ....you know get the maximum vacuum then go down 1inhg usually works for me but in this case i had to crank the dizzy clockwise quite a ways and the wires were pushing on the intake manifold before i got a halfway decent run.

After I went about as far as i could go clockwise i took it for another run, and holy crap, im weighing a good 7000lbs right now if not more with the 454 in the back and all my other crap and it will push me back into my seat however I still could not really pass 5000rpm at WOT 1st gear even though i know that i could reach 6000rpm a few weeks ago.

I will check to see my timing mark tomorrow, I will try setting it between 0 BTDC and 4 BTDC since this engine rebuild seems to like advance.

My power curve currently levels off near 4500 when i notice im not accelerating as quick

I just hope this helps someone else one day that is having problems.

Another issue im still having is it wants to cut out when im holding the throttle slightly open for cruising. was almost killing the engine with the inital timing i had, and after the turn clockwise it seems to have gotten better but you can still feel it bog down the surge back to life

[MuddiGGEr25]

Ok so got the replacement dizzy installed and re-installed my 369 module and my cap/rotor that were replaced roughly 4000ish miles ago.

Used the timing light at the shop to set timing, it is now at 1 BTDC, my "guesstimate" where it was running decent was about 8BDTC

Fuel pressure has not been tested although i am pretty sure its not my culprit.


I got the same hesitation as before just as bad as before, i tried disconnecting one sensor at a time then driving to see if it would improve, the only noticable difference was with the TPS unplugged it got so much worse i only made it 2 blocks and had to plug it back in. and by disconnecting the o2 it is not stumbling or bogging

I still have  a miss though but that has been there a while and i think ive found the culprit for that : When i was trying to turn the dist to time it i got nailed quite a few times and for a while now i have heard a ticking sound when its idling, then a few nights ago i noticed visible arcs from some of the wires to the exhaust or block. these wires were new old stock, meaning brand new sealed but i had them around for over a year before installing them.

I am going to probably replace them all and/or rob the wireset from the RV in the meantime


My results are now that I can accelerate and cruise with the o2 unhooked only

I can watch the miss very noticeably on the timing mark, like it jumps 4-10 degrees retarded when it happens.

I was able to climb up one of the steepest hills (4%) in town during rush hour I went WOT and was able to reach 5000RPM before i really didnt have much more power probably due to lack of timing and i could feel it missing more from about 3300-5000.

Throttle response is excellent currently

I know timing is probably too far back since I used to be able to climb that hill and reach 6000RPM everyday.

[MuddiGGEr25]

In case anyone was curious or if it helps the next guy or gal sometime in the future.

I installed the "rumble" glass packs and the miss was EXTREMELY noticable and actually was getting worse.

The weather got super cold the last couple days so i was putting off looking at it, however this is what i discovered and did to fix what i found

I checked the timing, i actually had it about 4-6BTDC and it was running pretty decent, however 2 days ago i adjusted the dist to 0 BTDC (by ear and using a vacuum gauge) no im not lying, i checked it with a timing light today and it was dead on 0 but at 0 BTDC i get that surge very noticeable at roughly 2000RPM again, so im thinking whatever they did during the rebuild that it likes a little more advance so i re-timed it using the method i use for my 77 450hp 302, max out the vacuum reading, then back it off just about an inhg, which put me about 3ish BTDC.


I got home and i knew the #1 had a miss, so i grabbed a new wire off the 400 and pulled off the #1 wire on the 350 and it literally was melted in half, no idea how since the split was up near the intake. i replaced it and now that miss is gone.


I notice a pitter patter in the exhaust but ONLY drivers side and i cant get past 5000ish RPM anymore. oil level is good and good oil in it. but I did the paper/dollar trick and it pulls it in and out with every revolution of the engine, and its steady. the otherside does NOT do this, and sounds perfectly normal.


From what i have read this is usually a sticking or bent exhaust valve or excessive overlap, im pretty sure the cam is not that aggresive. My next step will be to pull the valve cover off when it is running and make sure everything is tight and lifting evenly.


If that all checks out then my next check would be a compression test since some say the "flutter" could also be a headgasket


I think i may already need new plugs because of the pickup failing and the running lean for over 4000 miles, I will check them on the next warmish day.


Is there anything obvious im missing?


I reconnected the o2 to see if the broken wire was actually throwing off the o2 because of the misfire. My wife gets off work at 1130 and I will find out if it wants to run right.

[MuddiGGEr25]

Well tightening the rocker arms actually helped some, it can now get to 5800rpm again but it still struggling and spitting when i get past 5000, going to check the otherside this weekend after it rains, the dollar trick doesn't suck in as much anymore if at all but still a slight miss, which im not sure is wires, cap, rotor, or plugs. i think ill do a full tuneup before missouri. I have not been able to use the o2 yet since the surge still happens.