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Discussion Starter · #1 ·
Hello everyone! I'm a diy mechanic who has apparently bought a lemon of sorts. Let me start with the details of the truck.. as best as I know them at least.. the truck is a 94 k1500 with 118k on the odometer and good only knows how many on the motor. The truck originally came with a 350 but someone thought it okay to swap for a 305 from a 91 Chevy Caprice (some parts are different and that's what it lines up with) The truck blew a head gasket after running poorly for a short period of time so I repaired it. here is what has been done so far, please note that other than a few odds and ends I had laying around all of this stuff was bad..
Head gasket
Battery (had new one as spare from other car)
Starter (rusted out with broken wires, barely could turn motor)
Alternator (spare I had)
Battery cable (broken and corroded)
Iac (spare I had)
Ect sensor (broke old one doing heads)
Vacuum lines (because why not)
Timing chain (really needed it!!)
Plug wires and plugs
2 new injectors (both were leaky)
Fuel pressure regulator (found puddle of gas in tbi)
Distributor (old was broken by seller to disguise the problems)
Ignition coil (spare)
Multi switch
Brake switch
Flushed all fluids
Checked all fuses
Fuel filter

The truck will now start and idle fine but when it warms up it will occasionally backfire and when you put it in gear it will try to stall, it has nearly no power and Almost no acceleration. I just replaced the fuel pressure regulator and now I'm having issues trying to start it. Just crank and crank so now I'm thinking fuel pump. Im not sure how to test it on this truck. Or the relay for the fuel pump.. idk. It's frustrating. The previous owner zip tied and taped everything he could and at one point he ran into a problem with the pcv system and actually siliconed a tube where the valve goes and zip tied into the back of the tbi.. we all know valves don't cost as much as covers.. if anyone would be willing to help me further troubleshoot my mutt of a Chevy I would certainly be grateful!!
 

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Discussion Starter · #2 ·
Forgot to mention, when it idles it rests right around 1700 rpm, not 'fine' but more like a vacuum leak. I cannot seem to find any leaks at all though. it doesn't surge alot but it does change slightly sometimes by about 100 rpm or so. Also intermittent hesitation of throttle response (come and go) I have tested the tps, it shows .54 volts closed and 4.55 wot
 

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Heh, sounds like you've got similar problems as I. Get yourself a vacuum gauge... hook it inline with you vacuum connection... if its lower than normal, you've got some hunting to do... check out youtube, a guy on there explains well on what different readings are indicators of different symptoms.
 

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You could disconnect map vacuum hose and plug it, for a simple test,and plug the pcv hose off after for another test, sounds like you're running lean, after vacuum check, fuel pressure is needed to be checked
 

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Discussion Starter · #5 ·
Well I ran a compression test and got all but one cylinder in good health. Roughly 125 each cylinder but cylinder 8 was only 75. Tested 3 times and same results. Intake valve was burnt, weird but yea.. not broken just wont seat.. i still feel like i have a vacuum leak due to the high idle but im reluctant to test further due to the random backfire. Im saving the money to get a replacement head and gasket set. Im also debating on going with my l98 intake and ecm (performance chipped) from my old firebird at this point. But im wondering if it will mesh well with a 305 instead of the 350.. fuel spray seemed very neat and even on both sides and it has new components apart from a fuel pump, so i dont think fuel pressure is the issue. thanks for all the help so far guys
 

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Discussion Starter · #6 ·
Quick question.. I was curious about reusing the tbi harness to go tpi.. i dont see any difference between the 2 harnesses really except for one sensor and the quantity / style of injector wires. The donor vehicle was an 89 firebird with 5.7l maf sensor setup converted to map speed density.. how hard would it be given the striking similarity to just modify the tbi harness with the air intake temp sensor and injector clips (since tpi seems to be 2 sets of wires spliced into 4 sets each anyway.. ) or am I missing something?
 

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Discussion Starter · #8 ·
Problem boils down to money. A new head at the junk yard is 50 bucks to replace the bad valve with.. gaskets are about 100 bucks total.. crate motor is 600 at minimal.. the tpi intake is just something i have laying around. Figure for 10 to 20 bucks more (considering that i have fuel lines wires and various crap laying around) i might pick up 10 horses (not to mention the flippin torque this intake is known for) all in all i have invested very little in this suprizingly.. i do plan to find a 400 later to drop into this truck but they are not as common as id like. I would go with a carb at that point though..
 

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Zack, I have read all you have posted and the verdict , in my opinion is just as Silverado002 posted. You have a Junk engine my friend, It happens. You can get a GM stock replacement engine for $1800, or if your going to put a 400 in it ( I can't advice you more strongly to ( DO NOT DO THIS ). But is the engine and it's sensors hooked up ? Using a paperclip and if possible can you get anything out of the PCM ? You have OBD-I you should get some kind of " Trouble Codes" But you keep throwing parts into this truck and getting nothing back. Why do you think a junkyard is called a Junkyard ? You need to start with a clean slate, a 350 or a 383 professionally built. Your not going to be able just put parts in and expect a miracle. You need to get the truck back as close to 1988 as you can. I'm trying to say you need a place from which to measure from.

And lets say you get this 305 to work, how long is it going to stay that way ? I have an 88 Blazer with a stock 350 and I had a hel& of a time finding a trouble code 42 it was lighting up. Finally a member here told me what to do and as per his instructions the code is gone. There isn't anyway to put your truck to 1974, It's a 88 and it comes with electronics and the problems that goes with them. Do you have a "Service Engine Soon" Light ? is it lit? As it is you most certainly have a cylinder leaking. But even if you get it to run, it's still a 305 with a leaking head/gasket. There is everything from plugs and plug wires and oxygen sensor and 2 temperature sensors and I don't know what your doing with the vacuum leak ? If you have a small propane torch, and get a large piece of cardboard and cut it so it will block off the flow of the fan and hold the cardboard with one hand and turn on the propane torch and move it all around the Throttle body slowly and see if the engine speeds up and then you'll know where a vacume leak is.

Then do you know if the transmission and transfer case are OK ? My father told me once "Anything you get for nothing is usually worth it " If I were you, I'd gather up as many of the sensors as you can and I'm sure you have a Hayner's Repair Manual, and see how many are usable. Then do yourself a favor. Sit down and take a break and thing about getting a low cost, but GOOD Gen 1 V8 engine and a 350 ! There are shops who can test the distributor for you. I don't know where you live, but hit some of the local shops, and with a little luck you may score a decent 350. Here where I live in Pennsylvania, there in this little town, there are lots of shops who have swapped out a decent 350 to put a high HP 383 supercharged engine. Then the 425 pounds of decent 350 slowly get moved into a corner to collect dust. If you explain your "trouble/situation" a shop owner or customer might be able to sell you a good decent used 350 to start with. Install it and put the motor back to the way it was in 1988. Get it running and then, think about going forward. I think this is the cheapest way to go. Go to a paper stand and get a copy of "Hemmings Motor News, look through the whole thing I know it's got about 300 pages, but you might find a deal in there not too far from your home. And pray the transmission and transfer case are OK, but change the fluid anyway. Good Luck !
 
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