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Broken engine

Element

Element

1/2 ton status
Joined
Mar 23, 2007
Posts
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Location
WV
All right. Blazer's been sitting in the driveway for weeks for a few different reasons, so this is a new problem to me. Anyway, I took it out to play on some trails Saturday, and run into some issues. 1987, TBI350, TH350 swap (from 700r4).

For those that remember, I yanked the EGR valve off and had issues afterward. Got a new EGR valve, hooked it up, truck idles now. However, on a cold start, it stumbles - a lot - and idles low, although not nearly as low as it did with the EGR port blocked off. Another problem - at low rpms while driving, it has serious surge issues, almost like someone is turning the fuel on or off. Pop it in neutral, rev it a few times, or give it more gas while in gear, engine starts running fine. Third and most troubling problem, at low speeds (under about 20mph), with very light or no throttle application, the truck dies. It doesn't shudder, make any noises, nothing, I'll just be coasting along, and the truck shuts off like I turned the key to the off position. It only does it at low speeds, and only under no or very low throttle application. Drives fine around town as long as I stay in the gas.

Parts I've replaced thus far:
Plugs
Plug wires
Cap
Rotor
EGR valve
Coolant temp sensor
Battery
Battery terminals
Fuel filter
Air filter

I've had the truck scanned for codes and nothing is coming up. I'm completely stumped. I'm really concerned about the truck just cutting out, as it means I can't drive it until it's fixed, but I don't know what could be causing it. I thought it could be a bad ignition switch, as sometimes when it cuts out and I pop the truck in neutral, I can't turn the key (not 100% if that's not related to a bungled TH350 swap or not). However, it seems if that was the case, the truck cutting out wouldn't be speed related - it could cut out at any time. I thought it could be the TPS showing some sort of problem at low or no throttle, but there wasn't a TPS code in the computer (although from what I've been told, OBD1 is a lot less sensitive and less likely to throw a code than OBD2 systems). I thought it could be related to the baffle in the gas tank being loose, but the engine dying isn't related to any specific off-camber situation (it's happened when the truck is on perfectly flat road, just cruising along). I thought it might be an issue with the fuel pump cutting out, but again, it seems like that would be more likely to happen at higher engine loads than minimal engine load.

I'm completely out of ideas here. This truck has been nothing but an absolute headache from the day I bought it, and I'm half tempted to sell the damn thing right now, but I doubt I could get what I need to pay it off.
 
My best guess is a failing ignition module or pick up coil. When the pick up coil fails it cuts the signal to the fuel pump as well.
 
Probably a stupid question, but I'm used to coil on plug, so...

The ignition module is the rectangular box that the center wire from the cap goes to? The pick-up coil is...?
 
yes the lil box where the center from ur cap goes too. id check ur fuel pressure, if its not the coil. also double check ur ground wires
 
The ignition module is the electrical piece that has 2 wire connectors plugged into it that mounts inside the distibutor, the pick up coil is also located inside the distributor and in order to change it the distributor must come out and be taken completely apart.
 
Changed the ignition module, no dice - truck still does the exact same thing. I did notice, when I put the cap back on the distributor, that the whole assembly would twist back and forth. Could that be related to the issue?
 
Did you also change the pick up coil inside the distributor? You have to pull the distributor and take it completely apart to change this piece. If this piece goes bad you will have no spark.
 
4X4HIGH said:
Did you also change the pick up coil inside the distributor? You have to pull the distributor and take it completely apart to change this piece. If this piece goes bad you will have no spark.
Click to expand...

Haven't changed that because I'm not too sure on how to correctly disassemble and reassemble the distributor.
 
Element said:
Haven't changed that because I'm not too sure on how to correctly disassemble and reassemble the distributor.
Click to expand...

(1) remove distributor from vehicle
(2) remove roll pin holding the distributor gear on
(3) remove distributor gear (sometimes it needs to be pressed off)
(4) remove the distributor shaft (sometimes it has gunk caked on the shaft and will need some "love" to remove it)
(5) remove the clip on the top that holds the pick up coil (you must break the clip, the new pick up coil comes with a new clip)
(6) remove old pick up coil
(7) install new pick up coil
(8) to reassemble reverse instructions
 
4X4HIGH said:
(1) remove distributor from vehicle
(2) remove roll pin holding the distributor gear on
(3) remove distributor gear (sometimes it needs to be pressed off)
(4) remove the distributor shaft (sometimes it has gunk caked on the shaft and will need some "love" to remove it)
(5) remove the clip on the top that holds the pick up coil (you must break the clip, the new pick up coil comes with a new clip)
(6) remove old pick up coil
(7) install new pick up coil
(8) to reassemble reverse instructions
Click to expand...
Will I need to reset the timing afterwards? Don't have a timing light.
 
yes, timing will need to be set once the distributor is reinstalled. You can make note of where it is now and be close but a light will be needed to check and correct the timing.
 
yes you will...OR before you yank dizzy check wehre the vac advance is pointing adn reinstall dizzy EXACTLY in that spot, and make sure that before you pull it out you observe where the rotor is too.

and i am also witht he pickup coil...my truck was running crappy too, i just figured it was bad gas. 10mins down the road IM DEAD, mine went bad...

I had hard start when hot, surging, felt like something was holding me back when i stomped it.

i have yet to fix it...haha but im hoping that htis will solve my above problems.
 
This is of out on a limb but have you checked ALL your vacume hoses to the tbi unit. I had one that woud surge die and do all sorts of stupid s*&t and the guy i bought it from could'nt figure it out, but come to find out it was just a vac line wasnt connected to the throttle body. It took me 5 min to fix a gremlin that would have killed my wallet.
 
This is the exact situation with my 88 Astro 4.3 TBI. I went through everything that is listed in this thread, and finally broke down and replace the fuel pump as a last resort. The problem was solved. Never happened again. It wouldn't matter what I was doing, as I let off the gas to stop or even slow down it would die. No codes on computer, nothing obvious, but the fuel pump was the culprit. It may not be the case for you, but it is a definate check to perform, as mine wouldn't do it under load. Never made sense, but it was the problem.

Edit: Just saw the post about the fuel pressure, mine showed correct fuel pressure at idle, it would only have the problem when I was in gear. Basically the fuel pump would cut out as I slowed down or let off the gas.
 
Last edited:
scooter122983 said:
This is of out on a limb but have you checked ALL your vacume hoses to the tbi unit. I had one that woud surge die and do all sorts of stupid s*&t and the guy i bought it from could'nt figure it out, but come to find out it was just a vac line wasnt connected to the throttle body. It took me 5 min to fix a gremlin that would have killed my wallet.
Click to expand...

Yeah, even to the point of spraying a little carb cleaner around the TBI unit while the truck was running - didn't rev up, nothing, idled exactly like if I hadn't sprayed anything.
 
lectric80 said:
This is the exact situation with my 88 Astro 4.3 TBI. I went through everything that is listed in this thread, and finally broke down and replace the fuel pump as a last resort. The problem was solved. Never happened again. It wouldn't matter what I was doing, as I let off the gas to stop or even slow down it would die. No codes on computer, nothing obvious, but the fuel pump was the culprit. It may not be the case for you, but it is a definate check to perform, as mine wouldn't do it under load. Never made sense, but it was the problem.

Edit: Just saw the post about the fuel pressure, mine showed correct fuel pressure at idle, it would only have the problem when I was in gear. Basically the fuel pump would cut out as I slowed down or let off the gas.
Click to expand...

Exact same problem I'm having...does it as soon as I let off the gas and go to brake when going around a corner. Fuel tank/pump/sending unit is definitely on the list, as the sending unit is dead and the baffle in my gas tank is broken, just haven't had the spare cash to buy the parts.

I know I'll probably get reamed for this, but how much would a regular shop charge to replace the pick-up coil? Truck has to go in for an inspection ASAP, and it'll be going to the shop that did my ball joints ($160 for all 4). Given how busy work is and how little time I have to work on anything, if it's not likely to be too expensive, that might be my best bet.
 
Dead sending unit, broken baffles, how do you know this isn't simply a bad hose from the pump to the fuel lines?

I wouldn't spend another dime on this truck until you drop that tank and replace it.

Even if it ISN'T the problem, it's A problem, and needs fixed.

Besides, it's happened to others. A split line, bad wiring in the tank, etc. There is no way I'd even waste time on any more parts guesses if you know the baffle is floating around in the tank, banging that sending unit (and pump, and fuel lines) around.
 
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