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Discussion Starter · #1 ·
As I mentioned in my introduction, I have a 1988 Chevy 1 ton, it has Stahl service body on it. I am the second registered owner. It as originally titled to the Arizona Department of Natural Resources. More about that later.
I bought the truck in 2012. After doing a few things to it, it has always run very well. It only had 75K on in when I bought it. While driving a couple of weeks ago, I noticed a ping, or light tappet noise or something, I'm not sure. ,I added some Marvel Mystery Oil. My dad swore by that stuff. It didn't help. Then a few days ago while driving, it sort-a stumbled, but came right out of it. Then I noticed my volt meter was pegged to the max. This can't be good. Looking things over I found some burnt and crispy wires near the starter and exhaust manifold. One of the wires lead from the positive battery post to a junction block on the firewall. Another wire went from the starter solenoid to the ignition switch. The third was the wire going to the knock sensor. I replaced all the bad wiring, the knock sensor, and changed the oil. I don't know if the pinging (if it is pinging) and the burnt wires are connected in any way. All wiring is good now, and the volt meter is back to normal, but the truck has a slight hesitation and stumble when accelerating from a stop. It is a very slight hesitation, but it's there. Also, it doesn't seem to start as quick as it use too. It takes just a bit more cranking it seems, Back in the old days I would have replaced the points, set the dwell, and checked timing, I did order me a timing light, so I can at least check that. My question is, could the shorting of the wires damaged my ignition control module (ICM) in the distributor, or if it had been damaged, would the truck run at all? Is there something else I should be looking at?
Thanks for any help. Greg
 

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As I mentioned in my introduction, I have a 1988 Chevy 1 ton, it has Stahl service body on it. I am the second registered owner. It as originally titled to the Arizona Department of Natural Resources. More about that later.
I bought the truck in 2012. After doing a few things to it, it has always run very well. It only had 75K on in when I bought it. While driving a couple of weeks ago, I noticed a ping, or light tappet noise or something, I'm not sure. ,I added some Marvel Mystery Oil. My dad swore by that stuff. It didn't help. Then a few days ago while driving, it sort-a stumbled, but came right out of it. Then I noticed my volt meter was pegged to the max. This can't be good. Looking things over I found some burnt and crispy wires near the starter and exhaust manifold. One of the wires lead from the positive battery post to a junction block on the firewall. Another wire went from the starter solenoid to the ignition switch. The third was the wire going to the knock sensor. I replaced all the bad wiring, the knock sensor, and changed the oil. I don't know if the pinging (if it is pinging) and the burnt wires are connected in any way. All wiring is good now, and the volt meter is back to normal, but the truck has a slight hesitation and stumble when accelerating from a stop. It is a very slight hesitation, but it's there. Also, it doesn't seem to start as quick as it use too. It takes just a bit more cranking it seems, Back in the old days I would have replaced the points, set the dwell, and checked timing, I did order me a timing light, so I can at least check that. My question is, could the shorting of the wires damaged my ignition control module (ICM) in the distributor, or if it had been damaged, would the truck run at all? Is there something else I should be looking at?
Thanks for any help. Greg
The ICM on the distributor is only 1 part of the ignition timing system. You also have an ESC (electronic spark controller) and the knock sensor, which you already know about. The ESC is the flat box with I beleive 5 wires to it. It is located on a bracket next to the throttle body on the passenger side of the engine. These 3 items work together to control ignition timing. To check timing, you have to unplug a wire back close to the distributor. Otherwise, you're not going to get a correct reading. Once you check timing, the timing mark should be right at the '0' on the timing indicator next to the crankshaft pulley. One note, on my bone stock 1988 K1500 w/350 tbi, I cannot use 87 fuel with ethanol or it will be a dog and ping the valves at a certain load/rpm. I have to run either today's regular 89 octane or ethanol-free 87. 93 octane is just a waste of money by my calculations for my truck. I maximize my cost per mile with the ethanol-free 87. Also, keep in mind that ethanol dries out rubber fuel components on pre-ethanol machines. When I was running regular fuel in my truck back when it was a daily runner, I found the o-rings for the fuel lines at the throttle body only lasted a few years before cracking. Now that it only runs non-ethanol fuel, I havent had a problem.
 

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1988 C1500 Silverado, 5.7L with some go fast parts.
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The 1st thing I'd do is check your fuel pressure. GM says it s/b 9 - 13 PSI but, 11 - 13 is optimum.

When was the last time you changed the fuel filter?

How old are your normal tune up parts - cap, rotor, plugs, wires?

What size engine? For small blocks timing is set to TDC, for the 7.4 it's set to 4° BTDC.
 

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Discussion Starter · #5 ·
I have timed the engine to TDC. I have replaced the fuel filter. Checked all vacuum line connections, and generally looked everything over. I am considering removing ALL of the emissions control system components. Air pump, and anything else that goes with it. Has anyone done this to a TBI 350? Would you recommend it? If so, What all can (or needs) to be eliminated? Thanks Greg
 

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1988 C1500 Silverado, 5.7L with some go fast parts.
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I am considering removing ALL of the emissions control system components. Air pump, and anything else that goes with it. Has anyone done this to a TBI 350? Would you recommend it? If so, What all can (or needs) to be eliminated?
Removing emissions won't do much of anything for you unless, you get lucky and one of them is the cause of your issue. If you do, you'll need to modify your ECM so you don't get a nuisance SES light when it's looking for those components and their activity. Plus it is totally illegal, it doesn't matter if you're in an area where they don't have testing, it is a Federal law!

How about we try to solve your problem as cheaply as we can, what is your fuel pressure?
 

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I have timed the engine to TDC. I have replaced the fuel filter. Checked all vacuum line connections, and generally looked everything over. I am considering removing ALL of the emissions control system components. Air pump, and anything else that goes with it. Has anyone done this to a TBI 350? Would you recommend it? If so, What all can (or needs) to be eliminated? Thanks Greg
My 1988 w/350 has the air pump on it as well. I put a new pump on it a few years back after figuring out it's not worth the hassle of taking it off. If you get caught, it's big trouble. Plus you'll have to remove the tubing from your exhaust manifolds and plug the holes, and then you'll have a check engine light forever because the system is tuned for the emission stuff. I suppose you could pop an eprom from a truck without an air pump, but that's just too much work. The emission system on these trucks is very primitive. Much easier to fix your original problem than try to create more problems. I've owned my truck for 24 years, and trust me, it's easier/cheaper/simpler to just fix the known issue!

To check your fuel pressure, you'll have to take the fuel line loose on the back of the throttle body to install the test adapter. It's not hard to do, but I recommend getting new fuel line o-rings first and put a new o-ring on the line when you're done.
There are two connections on your diagnostic port you can cross to make the fuel pump run without running the engine. Otherwise, you'll only be able to see fuel pressure when the pump primes, and the pressure goes away pretty quickly once the pump stops. I like to cross those terminals and make the pump run a minute or so to get a good test. I will post the terminal info below:

To check codes, put a paperclip between A and B, then turn key to ON (you might already know this)
To make fuel pump run for testing purposes only, with engine off and tester connected, connect terminal G to ground.

Rectangle Font Line Parallel Number



Three things that are a must to own if you're doing all your own work:
1. Chilton's repair manual
2. Haynes repair manual
3. Snap on MT2500 scanner with the GM diagnostic and troubleshooting cartridges. Can be picked up for a couple hundred bucks. Check Ebay. It will pay for itself with the first repair!

When my truck acted up a few years ago, this helped me find my bad injectors. I was able to watch my sensors while driving. The sensors were all within parameters, fuel pressure was good. Popped in new injectors, and problem solved. That scanner is worth its weight in gold.

 

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1988 C1500 Silverado, 5.7L with some go fast parts.
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I've noticed that. One is fuel return. Which is which?
The bigger (3/8") line is pressure, the smaller (5/16") line is return.

Another way for monitoring pressure is permanently mounting a gauge on the TB.

Here's mine with an AFPR - been on there for ~3 years now.
Automotive tire Motor vehicle Rim Gas Machine tool


Here it is with an 28 LB spring set at 28 LBs while idling.
Motor vehicle Automotive tire Hood Automotive design Bumper
 

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Discussion Starter · #11 ·
Both of my lines are the same size. But in the end I did figure it out. I turned on the key and the gauge did nothing. :confused: I jumped pin "G" to ground, and the gauge did nothing. I didn't think this could be right as I drive this truck every day. I moved my tester directly to the line in front of the fuel filter. The gauge did nothing. Again..:confused: I got to looking at the gauge. The hose has no provision for depressing the Schrader valve. I took the Schrader valve out. This time when I turn the key on, the gauge goes to 10. What should it be?
Incedentally, jumping pin " G " , on the diagnostic port to ground, does nothing.
 

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1988 C1500 Silverado, 5.7L with some go fast parts.
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This time when I turn the key on, the gauge goes to 10. What should it be?
IMO 11 -13. (see post #4) You're low. If you do replace the fuel pump, I recommend an ACDelco EP381, from a 96 Vortec. It's more robust and will give you plenty of volume, your regulator will work fine with it.

Incedentally, jumping pin " G " , on the diagnostic port to ground, does nothing.
No, you're supposed to apply 12V to it.
Rectangle Font Parallel Pattern Number
 

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Discussion Starter · #13 ·
I moved the pressure gauge to the TBI inlet port. Turn on the key, I get 10 psi. Apply 12V to pin "G", I get 15 psi.
When I look up ACDelco EP381 I see prices from $170 to $50 ????? It also says 60 psi pressure. Will I need a fuel pressure Regulator to use with this pump? Can it be mounted on the frame rail of the truck, before the fuel filter?
 

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1988 C1500 Silverado, 5.7L with some go fast parts.
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It also says 60 psi pressure. Will I need a fuel pressure Regulator to use with this pump? Can it be mounted on the frame rail of the truck, before the fuel filter?
As I said your TBI regulator will work fine, the pump is rated 155L/Hr at 60 PSI (IIRC) and will give you more at 13. The pump from a 96 is a direct replacement for your OE pump, it even comes with the connecting hose. If you find one for $50 it's probably a Chinese knock off.

 

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IMO 11 -13. (see post #4) You're low. If you do replace the fuel pump, I recommend an ACDelco EP381, from a 96 Vortec. It's more robust and will give you plenty of volume, your regulator will work fine with it.


No, you're supposed to apply 12V to it.
View attachment 173967
My bad. It's been a few years since I last did it. Now, I remember running a hot wire from the cigarette lighter. Thanks for correcting that!
 

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I believe my present pump is in the tank. Can this pump be mounted on the frame rail, ahead of the filter?
No, the filter is intended to be pushed through, not sucked through. It will implode the element. Plus, the fuel lines are only flex lines at the pump and throttle body. Along the frame, they are metal tubes. Best to keep it hooked up as intended. I neatly cut a square hole in my bed floor right above the pump, then went to the junkyard and cut a section out of a rotted bed to lay over the hole. Slid my bed liner back in, my bed is intact, and fuel pump replacement takes less than an hour. No more dropping the tank! I've put 3 pumps in it in the last 24 years. After dropping the tank the first time and propping up the front of the bed the second time, I took a more direct approach the 3rd time! Farmer ingenuity, but I plan on keeping my truck until I die then it can haul my casket to my final resting place. Since you have a service body, hopefully you can make a fuel pump access as well with a little creativity!
 
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