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Username Post: 1988 5.7 TBI ignition problem        (Topic#277078)
dc_motruck 
Forum Newbie
Posts: 53

Loc: Rural Missouri
Reg: 02-01-10
02-27-12 09:38 AM - Post#2195844    

I am not a genius, but I don’t think I am too dense either… But here is a problem I just cannot figure out! Sorry for the long and drawn out explanation, but I think it will help with a diagnosis.

Chevy 2500 4x4, 5.7, manual trans

Truck died and would not start back up… crank and crank but would not start.
Towed home and investigated – had fuel and spark. I turned the distributor while it was being cranked over. It began sputtering and backfiring but started and ran really rough.
From past experience and for a “shot in the dark” I replaced the ignition module on the distributor – engine ran the same. Unhooked the “timing wire” and ran the same. Replaced the distributor cap and rotor, ran the same.
So my next step – intuition told me it had to do with timing. So I pulled out the radiator etc. and removed the timing chain/gear cover. Marks were off about a quarter turn; the chain had slipped.
Replaced gear and chain, put it back together (lining up the timing marks correctly) – didn’t think it would ever start, but finally did. But ran terrible. Double checked distributor/timing, everything checked out. At one point it did run/idle with timing way advanced – but when trying to set the timing at zero it would start sputtering at about 10-12 degrees. It would not run when the timing was brought down below that.
I even checked the fuel pressure at this time – pressure was OK.
From a truck (same year and engine) that would run, I pulled the distributor (with module) and installed and set timing. Same thing, will not run (still has spark and fuel).
Now I am really stumped at this point…
My thought was again, the timing. So I took it apart again, to see if the chain slipped, again, for some reason. Nope, everything was still lined up correctly.
Reassembled, pulled distributer and reset the timing - #1 at TDC, on compression stroke, etc. same as before. Would not run.

Now for an oddity we noticed – when it was “sort of running” we attempted to set the timing to zero, we noticed that the timing light did not have a steady flash, it was a bit erratic. We thought that the timing light itself was bad, so I borrowed a different one and we got the same behavior, erratic flashing. Seems that there is an intermittent ignition problem?

My next step: I am going to pull the distributor cap and wires from the running donor truck to see what happens.

My questions at this point are:
Could this be anything other than a cap/plug wire problem?
With the “timing wire” unhooked, can any of the other electronic components be having an influence on the timing/spark?
Could it be the coil, pickup coil, or other ignition module such as the spark control module? Since I put in a distributor (from a running truck) I would not think it is the pickup coil…
Or could it be the computer (ECM) itself?

Any ideas are welcome!



 
Low priced Genuine GM Auto Parts
kberger 
Member
Posts: 36

Loc: Rockwall, Texas
Reg: 07-28-04
02-27-12 02:27 PM - Post#2195943    
    In response to dc_motruck

I think you may be right about the ECM being bad. Maybe it's only running in the "limp" mode?
1964 C-10
350ci/260hp crate
Turbo 350 transmission
TBI Conversion


 
jham0077 
"3rd Year" Silver Supporting Member
Posts: 505

Loc: Greenville, Il.
Reg: 11-04-11
02-27-12 08:20 PM - Post#2196093    
    In response to kberger

Ohm your cts(coolant temp sensor, by the water neck), it may be bad. The direcions are in the FAQ's. Swapping whole distirbutors rules out the pick up coil. You should be able to swap ECM's I think. I would wait for someone more experienced to OK that though.
Keep throwing money at it, it'll get better...
95 Tahoe 5.7 w/5 spd
Gone but not forgotten,
87 LWB 4x4 5.0 w/3 spd granny,
84 SWB 4x4 5.7 w/3 spd granny,
93 Full Size Blazer 5.7 w/5 spd,
97 Step-side Vortec w/5 spd.
I like shifting gears.


 
62chevy427 
"8th Year" Silver Supporting Member
Posts: 1793
62chevy427
Loc: laurens sc
Reg: 04-13-06
02-27-12 08:57 PM - Post#2196106    
    In response to dc_motruck

try replacing the coil.
56 bel air ((since 2002)
62 impala ss (since 1965)
65 el camino (since 1969)
66 nova (since 1987)
67 malibu convertible (since 1981)
72 el camino ss454 (since 1985)
83 gmc 4wd (since 1991)
95 impala (new)
14 camaro (new)


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
02-27-12 10:20 PM - Post#2196144    
    In response to 62chevy427

you can ohm out your coil as well but off hand I do not know how much resistance to expect. Also I would take the ignition module out and have it tested at a parts store.
98 Silverado k1500 4x4 350


 
dc_motruck 
Forum Newbie
Posts: 53

Loc: Rural Missouri
Reg: 02-01-10
02-28-12 08:38 AM - Post#2196240    
    In response to 355Cheyenne

Thanks for the replies…

It may be a couple of days before I can get back to working on this thing, but wanted to reply to your posts. Not too many free evenings this week.

My donor truck is an automatic and the truck I am working on is a manual transmission – I do not think the ECM is compatible to do a swap/test. Anyone know?

Regarding the ignition module (355Cheyenne), I assume you mean the module that is attached to the distributor under the cap? (I have had different people use various terms for the same thing) I really don’t have a place that will/can test modules, any modules…that’s another story. They always look at me odd like I asked for a kidney or something. I did purchase a new module when this all started – so I am getting the same results with 3 different modules (the original, the donor distributor, and the new one).

I am going to look for specs on testing the coil and will test it and the coolant temp sensor just to rule those out or if they are bad. The coil does sound like it may be part of the problem due to the erratic spark issue.


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
02-28-12 02:04 PM - Post#2196345    
    In response to dc_motruck

yeah I was referring to the ignition coil but if you changed it out a couple times, forget that.
98 Silverado k1500 4x4 350


 
jham0077 
"3rd Year" Silver Supporting Member
Posts: 505

Loc: Greenville, Il.
Reg: 11-04-11
02-29-12 01:37 PM - Post#2196746    
    In response to dc_motruck

"They always look at me odd like I asked for a kidney or something.", that's the look I got too. Brand new, probably $10k machine sitting there to test any thing you wanted to and the guy didn't know how to use it. And he actually said that. So, not alot of faith in the test. New module it is then. I replaced the pick-up coil in the distibutor at the same time.
Keep throwing money at it, it'll get better...
95 Tahoe 5.7 w/5 spd
Gone but not forgotten,
87 LWB 4x4 5.0 w/3 spd granny,
84 SWB 4x4 5.7 w/3 spd granny,
93 Full Size Blazer 5.7 w/5 spd,
97 Step-side Vortec w/5 spd.
I like shifting gears.


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
02-29-12 02:58 PM - Post#2196777    
    In response to 355Cheyenne

  • 355Cheyenne Said:
yeah I was referring to the ignition coil but if you changed it out a couple times, forget that.




bah, ignition module I meant to say.
98 Silverado k1500 4x4 350


 
drifterdude 
Frequent Contributor
Posts: 1285

Reg: 09-04-08
02-29-12 03:03 PM - Post#2196781    
    In response to jham0077

  • jham0077 Said:
"They always look at me odd like I asked for a kidney or something.", that's the look I got too. Brand new, probably $10k machine sitting there to test any thing you wanted to and the guy didn't know how to use it. And he actually said that. So, not alot of faith in the test. New module it is then. I replaced the pick-up coil in the distibutor at the same time.




Sad thing is if its the machine im used to the parts houses having. They walk up to it touch the screen select what item they want to test and it will show them on screen how to hook it up and then they just touch the test button to start it and it simply says pass or fail.....

I am so used to using autozone for the disco I get and the people there actualy not arguing with you when you get a part for a vehicle that does not cross over in the computer (orileys and advanced love to say oh that wont work its wrong your wrong blah....)

I actualy use the machine myself often Walk in if not in use let them know what I am testing and they will say go ahead. I know not every place is laid back but if you cant fallow a on screen setup that reads like a picture book then your a complete dumba**

92 K1500:350 bored 30 over,built 700r4,Comp extreme energy cam,double roller timing set,shaved heads,Rancho RS9000XL series shocks with wireless my ride system,35 inch Mickey Thompson Baja Claws,Relocated 4x4 switch to rocker on Dash.
Other mods..


 
dc_motruck 
Forum Newbie
Posts: 53

Loc: Rural Missouri
Reg: 02-01-10
03-01-12 08:29 AM - Post#2197097    
    In response to drifterdude

Yeah, I just cringe when I have to go to a parts store… ANY parts store.

OK, had a chance to tinker on this thing last night. Here is where I ended up for those of you following along (and hopefully it may help someone in the future figure out a problem).

Installed distributer and cap & wires from donor truck (truck that ran) on this truck. (#1 cylinder tdc, etc. as per normal procedure)
Had someone crank it while I slowly turned distributer – it coughed, choked, sputtered then finally started.
Let it run for a few minutes to warm up a little… then tried to tweak the timing a bit by turning the distributer a little more… But what I found is that if not in a “sweet” spot it would die. But if turned back up a little it would start again.

Put timing light on to see where it is running as is (timing wire to ECM is unhooked at this point too). Getting good “flashing” from light this time…

Now for the kicker – it is running when the timing is wayyyy advanced. But when trying to dial it down to zero, the engine will die at about 10-12 degrees. There is no way to get it to run if timing is adjusted below that…

This is where I am lost, again/still.

What could be the cause of that? I seem to be back to the original circumstance. I did forget to Ohm check the coolant sensor before I started, but did check it after I got to this point… Not sure if I am getting a bad reading or what but when I checked it (engine was warmed up with sensor still in manifold), a # would flash on my digital reader then it would immediately go to “000”. So does this mean the sensor is bad? So now I am debating on whether to drop the $25 on a sensor to “see” if that makes it better? Or would that even affect the run-ability when tweaking the timing?

Someone also mentioned to me the MAP sensor… if this sensor is failing, could it be part of this problem? A MAP sensor looks to be about $60, I hate to throw that much at it… Guess I will read up on how to test the MAP sensor before I dump more $ on this project.


 
drifterdude 
Frequent Contributor
Posts: 1285

Reg: 09-04-08
03-01-12 04:43 PM - Post#2197253    
    In response to dc_motruck

have you turned the motor over to TDC compression stroke on #1 to verify the damper has not slipped? I re read didnt see anything say you had.

The damper is 2 pieces and the outer part can slip and make read improper when timing the motor. Set to TDC #1 compression make sure the damper lines up with the 0 or right close to it and ensure its reading proper.
92 K1500:350 bored 30 over,built 700r4,Comp extreme energy cam,double roller timing set,shaved heads,Rancho RS9000XL series shocks with wireless my ride system,35 inch Mickey Thompson Baja Claws,Relocated 4x4 switch to rocker on Dash.
Other mods..


Edited by drifterdude on 03-01-12 04:44 PM. Reason for edit: No reason given.

 
dc_motruck 
Forum Newbie
Posts: 53

Loc: Rural Missouri
Reg: 02-01-10
03-02-12 07:42 AM - Post#2197441    
    In response to drifterdude

Yep, I did check that. I had read that in someone elses post and that seemed like a possibility. But the mark lines up like it should when setting #1 at TDC compression stroke. This thing is really stumping me. It's an old truck that I hate to spend a lot of money on, but now I feel like I have to figure it out for my own sanity!

I did check the MAP sensor (using volt meter and vacuum pump). It checks out OK. Voltage steadily changes when vacuum is applied. And it holds vacuum...

I havent changed the coolant temp sensor yet, but am going to invest. (Sent someone else to pick up the sensor, but Parts Store gave them the wrong one... typical #@$#).

Can this be a coil problem (I think 62chevy427
suggested this)? If the coil is getting weak, can it be producing enough spark to run, but not enough spark to handle a load?

 
dc_motruck 
Forum Newbie
Posts: 53

Loc: Rural Missouri
Reg: 02-01-10
03-05-12 08:02 AM - Post#2198709    
    In response to dc_motruck

Finally… the saga comes to an end.

Bought new CTS from “O’Robberys” after a brief debate about how they “didn’t” sell the wrong one last time… Not sure they appreciate my humor, anyway…

Replaced CTS and tried to start.. crank, crank, crank – no start.

Ok, now what?

Replaced coil with a known good coil from donor truck.
Tried to start… crank vrooommm started up. Tweaked distributer slightly, then it idled fast (as it should on a cold start). Let it warm up then hooked up timing light. Slowly turned distributer as my helper watched the timing mark. Turned down to zero degrees without stalling. Nice.
Tightened distributer hold down and shut off truck. Then disconnected battery ground and hooked up timing wire. Waited five minutes and fired right up and no SES light/codes.

It all came down to a bad coil basically. Excellent call 62chevy427.

I hope this helps someone else someday… sure made me scratch my head.


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
03-05-12 09:55 AM - Post#2198751    
    In response to dc_motruck

Thank you for reporting back!
98 Silverado k1500 4x4 350


 
Low priced Genuine GM Auto Parts
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