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Username Post: 88 350 TBI timing/ignition problem        (Topic#82788)
scott88 
Member
Posts: 5

Reg: 11-30-04
12-02-04 08:04 AM - Post#566005    

I have an 88 Chevy C2500, 2WD with 350 TBI. I have a similar problem that I have been working on for 2 years and had a GM mechanic stumped for over a year. The engine runs smooth sometimes and runs horribly bad at others like it is severely out of time, backfiring through the throttle body.

I replaced timing chain, injectors, tune-up and fuel pressure regulator. The mechanic changed out the computer, distributor and checked the ignition and MAP sensors. The problem persists. It is part of the electronic ignition system because when I disconnect the ignition bypass wire, the engine runs fine, no hesitation, smooth, etc. and I plug it back together, it runs awful. My truck had symptoms years ago, such as not idling well and at times run bad, but run good after shutdown and restart.

If anyone has enlightenment on this situation, I would be grateful if you could share you knowledge with me. How do the ignition module, electronic spark control and ECM work together with engine sensors??

Thanks

 
ICON 
Senior Member
Posts: 304

Loc: Western Mass
Reg: 09-01-04
Re: 88 350 TBI timing/ignition problem
12-02-04 10:19 AM - Post#566006    
    In response to scott88

Any ryhme or reason to the problem?? Happens hot or cold? Underload or idling? Was everything in Dist replaced w/new one?
'01 Tundra SR5 4x4 '05 Honda Foreman 500 4x4 '96 Yamaha Waverunner III


 
loudpedal 
Super Senior Member
Posts: 5010

Loc: corner of Walk & Dontwalk...
Reg: 07-28-00
Re: 88 350 TBI timing/ignition problem
12-02-04 10:46 AM - Post#566007    
    In response to scott88

check the coil resistance values when warm

check the distributor pickup for shorting/intermittents.

Check the dist reluctor and the top portion of the reluctor for rust at the dist shaft area. This is a common problem spot.

Check grounds at the EST module.

 
scott88 
Member
Posts: 5

Reg: 11-30-04
Re: 88 350 TBI timing/ignition problem
12-02-04 04:23 PM - Post#566008    
    In response to loudpedal

No ryhme or reason, sometimes it runs good when its cold, sometimes when hot. Runs bad about 90% of time. Seems to run good under steady state operation with a light load, as soon as you hit the gas quickly, it hesitates and sounds bad. If I go slow it is smooth. I drove it the other night and ran super, stopped and got gas, drove down the road and punched it and it started it again.

What I did notice is that if I bypass the ignition by disconnecting the connector, the hesitation and problems go away except for the effects of not having ignition advance.

 
scott88 
Member
Posts: 5

Reg: 11-30-04
Re: 88 350 TBI timing/ignition problem
12-02-04 04:26 PM - Post#566009    
    In response to loudpedal

Where is the timing advance controlled? Ignition module, electronic spark control? I disconnected the knock sensor and nothing changed. Could it be a bad ignition module? What is anyone's opinion of Auto Zone's checks on ignition module? (accurate or not)

 
1983G20Van 
Super Senior Member
Posts: 3223

Loc: Bedford, Texas, USA
Reg: 11-13-02
Re: 88 350 TBI timing/ignition problem
12-02-04 04:32 PM - Post#566010    
    In response to scott88

Check your tps voltage. It is the middle wire in the connector going to the throttle position sensor. With the key on, engine off back probe the connector with a DIGITAL multimeter (I CANNOT STRESS ENOUGH HOW IMPORTANT IT IS NOT TO USE ANALOG). You should get around .5 volts with the throttle closed. Slowly open the throttle while observing the meter. It should smoothly increase up to about 5 volts at wide open throttle. Another check you can do is check the MAP sensor. The map is the vacuum sensor (for lack of a better description). It should read about 3.5-4.5 volts with the engine off. With the engine idling the Map should put out about 1 volt. If you suddenly snap the throttle open it should go towards 3.5 or 4 volts followed by a reading of about .6 to .8 during decel (after blipping the throttle). It sounds like you possibly have a dead spot in one of your sensors.

The module checks are accurate as all they do is simulate the conditions in the vehicle. Just make sure that they run the test enough times to get the module warm. That takes 10-15 times, but one check takes about 15 seconds so it not that big a deal. I have seen alot of modules pass good when cool, but fail when warm. I do these checks all the time.
1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 
355Cheyenne 
Senior Member
Posts: 3762
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
Re: 88 350 TBI timing/ignition problem
12-02-04 04:40 PM - Post#566011    
    In response to scott88

kind of an older engine. when I rebuilt my 88 I had a problem with nocking even though I timed perfectly and it turned out that my outer ring on my balancer slipped over time and so my timing mark was off considerably. could this be your problem too? that your not timing the engine right because the mark is off on the balancer?


you might be able to tell by lining up the paint chips on it from the outer ring to the center piece. also if you just try advancing and retarding the engine to see if it improves or worsens.

oh yeah and my Map sensor was givng 100% load as it was bad causing miss fires up the carb, running too rich. sounds like you should start frome square 1 and get your self a good gm fuel injection book and test each sensore and veryfy you have perfect timing.
Tom
98 Silverado k1500 4x4 350


 
jritland 
Member
Posts: 14

Age: 64
Loc: Haines City, FL
Reg: 12-01-04
Re: 88 350 TBI timing/ignition problem
12-02-04 05:02 PM - Post#566012    
    In response to scott88

I have an 88 suburban that did the same to me. Left it parked for 6 months changing this and that, nothing helped.

It turned out to be the pickup coil. The coil checked good, using the meter test in the manual so it was not considered a cure and ignored. Finally a friend of mine told me to change it even if it did pass the meter test. $6.50 later for a new coil that fixed it made me a believer in changing the darn thing right off the bat in the future.
82 GMC 2wd P/U
86 S10 Blazer 4wd
88 & 89 2wd Suburban's
90 & 93 4wd Suburban's
90 K5 Blazer 4wd
94 2500 4wd P/U
95 2500 4wd Suburban
02 2wd ext cab P/U


 
1983G20Van 
Super Senior Member
Posts: 3223

Loc: Bedford, Texas, USA
Reg: 11-13-02
Re: 88 350 TBI timing/ignition problem
12-02-04 05:19 PM - Post#566013    
    In response to jritland

The distributer on his engine has already been changed as stated in his first post. That means the pickup coil too.
1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 
jritland 
Member
Posts: 14

Age: 64
Loc: Haines City, FL
Reg: 12-01-04
Re: 88 350 TBI timing/ignition problem
12-02-04 05:25 PM - Post#566014    
    In response to 1983G20Van

Then the question is, where did that dist come from? New or used? known for sure to be good? Everything else has also been changed that would have anything to do with timing.
82 GMC 2wd P/U
86 S10 Blazer 4wd
88 & 89 2wd Suburban's
90 & 93 4wd Suburban's
90 K5 Blazer 4wd
94 2500 4wd P/U
95 2500 4wd Suburban
02 2wd ext cab P/U


 
1983G20Van 
Super Senior Member
Posts: 3223

Loc: Bedford, Texas, USA
Reg: 11-13-02
Re: 88 350 TBI timing/ignition problem
12-02-04 06:08 PM - Post#566015    
    In response to jritland

Not saying that the pickup coil couldn't be bad but generally a bad pickup coil won't let the engine run(although a broken wire running from it will make the engine run very bad). The computer controls timing by using inputs from various signals. One bad sensor and the engine will run poorly. The ECM relys on look up tables cross referenced against inputs from the various sensor. Almost every sensor has an affect on advance. The map sensor plays a vital role in the timing advance. The "Main" spark table is just Map vs. RPM.
1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


 
jritland 
Member
Posts: 14

Age: 64
Loc: Haines City, FL
Reg: 12-01-04
Re: 88 350 TBI timing/ignition problem
12-04-04 02:14 AM - Post#566016    
    In response to 1983G20Van

Very true about the pickup coil. If it has an open or broke wire it won’t run. But, the pickup coil can develop shorted turns. There is no way to check for this with a DVM or continuity tester. With shorted turns it will cause crazy symptoms and make you (and the computer!) think the problem has to be somewhere else.

When this happened on one of my trucks, it caused the computer to call out EGR codes. Of course after changing anything and everything that could possibly have anything to do with EGR, I was still right where I started, just a little poorer from buying parts.

I had checked the pickup coil as specified in the factory manuals and by that it was good. I finally changed it anyway on the advise of a friend who worked in the motor pool for a large electric utility. He told me they could check good and still be bad and it turns out he was right! After I changed it and realized he was right, I took the old one to work with me. My day job is in electronics. I tested the pickup coil on a “ringer”. It is used to test coils for shorted turns and sure enough it tested bad.

After time, with the constant heating and cooling, the enamel on the wire in the coil breaks down and allows the fine wire to short to another turn. This cannot be detected with a regular meter.

Now the kicker. It can be more or less shorted depending on the temperature. The longer you work on troubleshooting , the warmer it gets. The warmer it gets, the worse it gets! More turns short and makes the symptoms change, chasing you all over the place trying to figure out what is going on. Then you quit and walk away and come back when it’s cold and find the symptoms have changed yet again. When it’s cold there may not even be any shorted turns so everything will work fine but as soon as it starts warming up the worse it gets making you pull your hair out trying to figure out what is going on. It can be enough to make a preacher cuss!

I learned my lesson well! Now, after about 80k miles, I just change it before it has a chance to cause problems.
82 GMC 2wd P/U
86 S10 Blazer 4wd
88 & 89 2wd Suburban's
90 & 93 4wd Suburban's
90 K5 Blazer 4wd
94 2500 4wd P/U
95 2500 4wd Suburban
02 2wd ext cab P/U


 
scott88 
Member
Posts: 5

Reg: 11-30-04
Re: 88 350 TBI timing/ignition problem
12-04-04 12:54 PM - Post#566017    
    In response to jritland

Thanks to all who are helping me diagnose the problem. It is a new distributor that our mechanic installed. It has new pickup coil, module, etc.

I spent the entire day further diagnosing the problem. I had a timing light hooked up to the #1 cylinder and watched the advance as I would rev the engine. If I would rev the engine slowly, the timing would advance until it hit a certain RPM and then would suddenly severly retard (20 degrees BTDC). If I would punch the throttle, it would severly retard immediately. If I bypass the computer controlled advance, it runs good and does not miss a beat. I will doulbe check the MAP sensor, since that is the sensor that would provide input if the throttle is punched.

Thanks again everyone for all your help. Keep it coming.

What is the purpose of the Distributor HI and LO references to the computer? Can I measure the signal for advance from the computer with a Multimeter. Does the computer give a varying voltage signal to tell the ignition module how much advance to move.

The engine has (2) ground wires, a smaller one in the back and a larger one underneath toward the front. Could one of these be a problem. I did ground the engine with jumper cables and it did not make a difference.

Scott

 
Trevorhoward 
Forum Newbie
Posts: 1

Reg: 07-27-12
07-27-12 09:27 AM - Post#2252677    
    In response to scott88

If your truck runs rough at idle and under a slight load it couls be the EGR sensor.Try unplugging the vacuum hose going to EGR valve if that works replace the egr sensor

 
Astro88 
Forum Newbie
Posts: 48

Reg: 02-09-10
07-31-12 02:03 PM - Post#2254226    
    In response to Trevorhoward

Ok, I thought I'd ask in this post, since I'm dealing with an 88 TBI 350 C-Series truck, and am having an ignition/timing problem. On friday, my buddy was driving it, and it started to really loose power, and would hardly run at all. In fact it stalled twice on him. Saturday, he brought it out, and I took it for a test drive. Man it really ran like crap. So I unplugged the "timing lead", as I wanted to find out IF that had any real effect on it. It did, but not much. Anyway, I put a timing light on it, and found it to be about 1.5 inches below the timing mark, so we "re-set" the timing. It ran real good again. I should mention, that this truck had just been resurrected from sitting in a field for 10 years, and has had the engine gone thru, along with the fuel tank, fuel pump, and sending unit replaced, along with a new knock sensor and O2 sensor. In fact just the weekend prior, we put another set of plugs in it, as it was running rough (he thought it needed a set), but not like friday. Fast forward to yesterday, and it started acting up again, and the timing got re-set again, and an 89 brain was tossed in (thinking the rodent wiz (from sitting 10 years) might have messed up the original one). Everything was good until this afternoon, until it just completely quit running (not stalled, but just shut off). Is this a possible ignition pick up failure? We put the old brain back in, and the truck would idle, but under load is a no-go. He's ready to swap it over to a carb (we did this to his 93 2500 already), IF we can't figure out why it keeps changing timing on it's own (the distributor was locked down in place, and wouldn't move at first). Also, there are no codes being indicated, which is throwing us for a loop. It had been running good for the last 3 months, but now it's undriveable. Any help offered is appreciated, as I've kinda run out of ideas to check.

 
someotherguy 
Moderator
Posts: 25155
someotherguy
Age: 43
Loc: Texas
Reg: 08-01-03
07-31-12 05:42 PM - Post#2254292    
    In response to Astro88

Are you checking (and setting) the timing with the tan/black wire disconnected - every time - 100% sure? If yes, and it's changing timing on you, 3 possibilities I can think of right off the bat, just be forewarned I woke up very recently

1. Wiring harness damage

2. Ignition module going bad/intermittent

3. Harmonic balancer slipping (though this wouldn't explain the change in how it runs)

Richard
94 C2500LD / 94 C1500 / 06 300C SRT8
Check out my truck shop projects


 
355Cheyenne 
Senior Member
Posts: 3762
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
07-31-12 07:47 PM - Post#2254332    
    In response to someotherguy

Not to be a jerk but WOW Zombie thread... Lets make a new thread. and I don't understand dumping decades of advancements for an older system because a part wears out and or fails in the system. I mean even if the distributor is just worn out, you would still need to swap that out to convert to carb, why not just fix the distributor? Also to add to the argument, likely the failure in the system now is still susceptible in a carb configuration.
98 Silverado k1500 4x4 350


 
Astro88 
Forum Newbie
Posts: 48

Reg: 02-09-10
08-01-12 07:10 AM - Post#2254441    
    In response to someotherguy

  • someotherguy Said:
Are you checking (and setting) the timing with the tan/black wire disconnected - every time - 100% sure? If yes, and it's changing timing on you, 3 possibilities I can think of right off the bat, just be forewarned I woke up very recently

1. Wiring harness damage

2. Ignition module going bad/intermittent

3. Harmonic balancer slipping (though this wouldn't explain the change in how it runs)

Richard



Yes, the tan/black wire is disconnected 100% of the time. It was reassembled last year, timing set, and was good up until about a week ago. Then it got re-set. I've been playing with these trucks and systems for about 10 to 15 years, and never had to re-set the timing on one. It's always been a set it and forget it deal. But...

1A)I suppose the wiring could be dammaged, but where would I look for it? It's still in the factory convoluted tubing, and it's not throwing any codes.

2A) I've always had them either work, or be dead. I've even had them die while backing out of the garage before.

3A) I had thought about that, but I don't see any evidence of it slipping. Re-setting the timing Saturday, brought the truck back to life, and ran great to and from the beer store. Something moved, but what? And why?


 
Astro88 
Forum Newbie
Posts: 48

Reg: 02-09-10
08-01-12 07:26 AM - Post#2254446    
    In response to 355Cheyenne

  • 355Cheyenne Said:
Not to be a jerk but WOW Zombie thread... Lets make a new thread. and I don't understand dumping decades of advancements for an older system because a part wears out and or fails in the system. I mean even if the distributor is just worn out, you would still need to swap that out to convert to carb, why not just fix the distributor? Also to add to the argument, likely the failure in the system now is still susceptible in a carb configuration.



I'm on other forums as well as this one, and I was just trying to use proper forum protocol (by adding to this current existing thread), otherwise I would have started a new thread.
It's NOT my truck, so I can't dictate what the owner can, or wants to do (other than fix it). This is his company work truck (he's self employed) and can't afford the down time sitting along side the road (not making any money).
I was just asking IF the problem could be the pick up coil, as the timing is changing on it's own. I've NEVER had a GM do that before! The engine itself is a 350HP 350 crate engine, so I doubt the timing chain (or gears) is worn out (causing a jumping in time). I listed above what some of the parts were that have been replaced in the last year (with some in the last 4 months). The rest of the components are OE 88 chevy. He'd really like to keep the FI, but IF it's going to keep leaving him stuck alongside the road, it WILL get converted (he's already told me this 4 times). I'm going over there later today, and swapping out the entire distributor (I've got 1 here), and I'm taking a spare ESC unit, along with a couple of other electronic parts (TCS,TPS, MAP, etc...), to see IF I can fix it.
Thanks for the help.

Edited by Astro88 on 08-01-12 07:30 AM. Reason for edit: No reason given.

 
62chevy427 
"8th Year" Silver Supporting Member
Posts: 1694
62chevy427
Loc: laurens sc
Reg: 04-13-06
08-01-12 07:39 AM - Post#2254451    
    In response to scott88

just for kicks,check the egr valve for proper opening,closing
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)


 
Astro88 
Forum Newbie
Posts: 48

Reg: 02-09-10
08-01-12 07:47 AM - Post#2254460    
    In response to 62chevy427

  • 62chevy427 Said:
just for kicks,check the egr valve for proper opening,closing



I saw that above too, and I'm taking my vacuum pump to check it as well.

 
355Cheyenne 
Senior Member
Posts: 3762
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
08-01-12 08:25 AM - Post#2254470    
    In response to Astro88

  • Astro88 Said:
  • 355Cheyenne Said:
Not to be a jerk but WOW Zombie thread... Lets make a new thread. and I don't understand dumping decades of advancements for an older system because a part wears out and or fails in the system. I mean even if the distributor is just worn out, you would still need to swap that out to convert to carb, why not just fix the distributor? Also to add to the argument, likely the failure in the system now is still susceptible in a carb configuration.



I'm on other forums as well as this one, and I was just trying to use proper forum protocol (by adding to this current existing thread), otherwise I would have started a new thread.
It's NOT my truck, so I can't dictate what the owner can, or wants to do (other than fix it). This is his company work truck (he's self employed) and can't afford the down time sitting along side the road (not making any money).
I was just asking IF the problem could be the pick up coil, as the timing is changing on it's own. I've NEVER had a GM do that before! The engine itself is a 350HP 350 crate engine, so I doubt the timing chain (or gears) is worn out (causing a jumping in time). I listed above what some of the parts were that have been replaced in the last year (with some in the last 4 months). The rest of the components are OE 88 chevy. He'd really like to keep the FI, but IF it's going to keep leaving him stuck alongside the road, it WILL get converted (he's already told me this 4 times). I'm going over there later today, and swapping out the entire distributor (I've got 1 here), and I'm taking a spare ESC unit, along with a couple of other electronic parts (TCS,TPS, MAP, etc...), to see IF I can fix it.
Thanks for the help.



I was just blown away because this thread dated back to 2004 and that was the last posting from the OP. The point to making a new thread is so that people don't get confused or lost in someone elses issues and trouble shooting. For example they may not offer advice because it was already offered to the other guy but they did not realize you had or had not tried it or if it was you or not. The fact that your user names are very similar adds to the confusion.

I know I am not helping by being picky but I am just saying and I am sorry if I am sounding like a turd, I am just saying that I think you could be better helped with a fresh new thread.

Anyway I think you will be set with what you are planning, new distributor and ESC. The only thing that could be a wrench in your work is the balancer may have slipped over time. It is hard to determine if they have slipped but sometimes you can look at paint chips and see they don't line up which can be an indication. Otherwise you need to get #1 to TDC by removing the spark plugs and using a coat hanger or something similar to confirm you are at TDC and then see if the line is lining up to zero degrees.

98 Silverado k1500 4x4 350


 
FLTCM 
Forum Newbie
Posts: 5

Reg: 08-11-12
09-18-12 10:41 AM - Post#2270920    
    In response to Astro88

My 88 Sub TBI 350 had the exact symptoms. Problem - It was a 3/4 inch split in the two inches of fuel line that connect the pump to the fuel system inside the fuel tank. Less than 1/4 inch of actual hole in the 3/4 inch split, because part of the split was on the connecting tube to the pump. Leading to the problem becoming a constant one was -lagging power, then idle cycled up and down continually until the engine got hot, then it idled high. Sometimes the 88 ran fine for a while, then lagged power. Shut it down and cool it for a while and it ran good again for a bit. But progressively got worse until it was not drivable. Code 44 then 22, 33 as I changed parts. Changed the MAP, TPS, IAC, PCV, O2 sensor, cleaned the EGR, reseated all wires and giggle tested, new plug wires, dist cap and rotor, coil, rebuilt the TBI, removed the catalytic converter and muffler (straight pipe), new intake manifold gaskets, new vac hoses, redid all grounds and, finally, changed the fuel pump and found the split. Pump is good, but changed it out while in there. Took 2 full months, probably 150 man hours, easy. Real ball buster.

 
Jake_42022 
Forum Newbie
Posts: 16

Loc: Tampa Florida
Reg: 09-14-12
09-18-12 03:21 PM - Post#2271001    
    In response to scott88

I would replace the igintion coil for sure very cheap sounds like a sensor is gone bad but works some of the time so it doesnt come on the ECU if ur SES light is on check the codes for goodness sake but if ur car struggles when u mash the gas i would look into the igintion coil and go double check all ur sparkplug wires and make sure they are plugged in securely in the dist. and sparkplugs

 
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