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Discussion Starter · #1 ·
So as the title states i have a 1989 C1500 Scottsdale with a 350 TBI TH700r4. I belive it has the stock gears though i was told it has 3.73. Anyhow there are a couple different things.
First it has to crank 4-5 times before it will fire on a cold start, Hot start it will fire up with 1/2 to a full crank. I cant find any vacuume leaks. Starter was tested and is okay. All grounds are fine(dunno if that would even affect this). I have checked pretty much everything i can think to check except the TPS.

Second of all when going down the road when i give it throttle to speed up it kinda bogs down, i have to pretty much stand on it so it will rev up( come out of OD) and gain speed. It doesnt matter if its in OD though. Does the same in D, i cant gain speed unless i make it downshift otherwise it boggs. It idles fine. Runs a little rich i can smell the gas in the exhaust but i also dont have a Cat.

Here is a Ful;l list of everything that has been replaced in the last 6 months. Fuel pump, fuel filter,(oil n filter), pcv, plugs, wires,Dist(complete with cap and rotor), Ignition coil(ACDelco), Rebuilt the TBI yesterday, New injectors, CTS, MAP sensor, EGR valve, reset the timing with a light( just put it at stock 0* BTDC). I cleaned but didnt replace the IAC when i rebuilt the TBI it was pretty dirty but seems to work properly.

I cant for the life of me figure out what is wrong. It idles perfect great throttle response. Just boggs when doing about 40-60 and i try to give it gas like to go up a hill. I have checked everything 100 times to no avail. I do get a soft code from time to time after driving for a while but since its a soft code and i dont have an OBD1 scanner i dont know what code it is throwing ( i know no help there):nono: The only parts i havnt replaced or thought to really check until recently are the O2 which is a $15 fix and the TPS which run about $55 here. i dont know if wither would cause the problems i am having.
**Note** i have an adjustable fuel pressure regulator and when i redont the TBI i raised it 2 full turns. Seemed to help a little on the low end but not where i need it. Also i do not have a Tach or Pressure gauge. Not that it matters one way or the other but it will still burn the tires off, but only if i hold the brake(doesnt like to "peel out"). Sorry for the Long post.
 

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Discussion Starter · #2 ·
So i was wondering if the accelerataion issue could be Valve related? Maybe something in the heads? Injectors spray perfect at all rpm ranges. IAC and TPS are good i have tested them. Maybe a Bad CPM/Prom? Just seems like bad throttle response. Throttle cable is good and tight though. Butterflies are spotless. Esp. now after the rebuild.) Oil looks great due for a change in about 700 miles though. Trans fluid looks good and doesnt smell burnt. I doubt changing the rear diff fluid would make a difference. I dont have a way of checking fuel pressure though but seeing as how i just replaced the pump and sending unit along with the filter and pressure regulator with no leaks i dont think it would be the issue.:smash:
 

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Discussion Starter · #5 ·
I am actually getting ready to pull the TBI back off, i heard you can test the injectors with a 12v battery and listen for a click. I know mine work so not sure that would do much. Now if this helps, i forgot to mention the truck was completely re-wired. The injectors and everything had a new harness put on. Maybe a ground is in a bad place uner the truck that i am not aware of? ill check a wiring diagram. I will let you know what my testing provides. Ill do the Scanner trick first.
 

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Discussion Starter · #8 ·
Grabbed a TPS from a junl yard 3 minutes down the roads from me and it works. Also when i took the TB off i took the egr off and there wasnt any carbon deposits and it was seating all the way. Holds vacuum. I hooked everything back up, Drove it about 30 miles (round trip) changed my oil. Didnt have an issue. I had reset the battery though. Had the neg off for about 45 minutes. If the SES light comes back on ill let you know. If it does it will do it on my way to work in the morning. Ill let you know. But for now that seemed to have done the trick. Also replaced the O rings on my fuel line and return line. Hopefully thats where it was bleeding off. Will find out in the morning when i go to start it for work. It would help knowing the miles on my motor, Body has 277k but motor isnt original. No clue about the miles on it. Also would a tranny flush n filter Blow my tranny like everyone says. I have never done it to be on the safe side. I believe its the original Trans.
 

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Discussion Starter · #11 ·
Well, Hard start is still there, cant find any leaks. Will i have to replace the entire pump/sending unit or can i just replace the pump? And i got the complete overhaul kit so i hope its not the wrong regulator. It was doing thjis before i replaced it. SES light hasnt came back on yet though so thats a plus, mainly just the hard start now.
 

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Discussion Starter · #14 ·
Well, Hard start is still there, cant find any leaks. Will i have to replace the entire pump/sending unit or can i just replace the pump? And i got the complete overhaul kit so i hope its not the wrong regulator. It was doing thjis before i replaced it. SES light hasnt came back on yet though so thats a plus, mainly just the hard start now.
Several years ago I had an 89 that came in to be checked out for a very similar problem.
Took some looking to find it, but....and I am not saying yours will be the same but....I found the wire to the pickup coil in the distributor were corroded almost in two. I replaced it and it must have been the problem because it fixed it.
Funny thing is it still had spark but wouldn't spray the injectors.
Must have been sending a signal that was too weak to Feed the Ignition and the ECM
That being said, the TBI system is very good at startup especially cold as it sprays the fuel, promoting atomization, unlike a carb that requires the fuel be siphoned through small orifices in the carb before it even atomizes .
A TBI is a very dependable cold starting system even in the face of -25 degrees and better.
I wouldn't worry about any timing chain problems at this point as it is a dual row chain and not the morse silent type. The dual row is used in roller cam engines because it is less prone to allow timing fluctuations due to design alone.
I would try spraying down the throttle and then try to start it first thing in the morning to see what you get.If it starts with a spray then fuel is lacking for some reason.
It would really benefit the diagnostic routine if you had a pressure gauge on the system to verify cold startup pressure or lack of, or slow to build pressure.
Better to diagnose than to throw parts at it.


One other option for cold startup fuel starvation (a presumptive test) would be to turn the key on don't crank, wait 2 seconds. This cycles the fuel pump by using the ECM 2 second pulse that turns the fuel pump on to prime the system. You can cycle the key 4-5 times. Be sure to listen to be sure the fuel pump relay is indeed cycling. Then after that see if you get a decent cold startup.
If that seems to help the startup situation the it is likely the pump check valve is not holding or the line in the tank between the pump and the fuel outlet line is leaking.


At any rate you really need to nail down if your cold start problem is fuel related.
Be sure the fuel pump relay will cycle and that it is powering the circuit
Get a fuel gauge and hook it up.
Stop guessing at it.
Well with a brand new dizzy and coil I don't think that would be the issue. However I am starting to believe the Check valve is bad causing fuel pressure bleed off.
 

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Discussion Starter · #16 ·
Fuel pump is kicking on, If i "prime" the system it only cranks 2 or 3 times. I dont think i am gonna get under that as i run 15w-40 in it. It's 6 cranks before fire if i dont turn the key on position and back off 4-5 times. On a hot start it fires right up, youd think it was MPI. TPS is good, IAC is great, i did rebuild the TBI and didnt adjust base-idle. Do i need to do that? I think the pressure is just bleeding off somewhere.:confused::confused::confused:
 

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Discussion Starter · #18 ·
Yes i have a digital voltmeter and have already tested the TPS. Its tested good. I will check the throttle. Fuel pump is new so i really hope it isnt the issue. Not expensive but just a waste of money. I dont have a scanner for live data and i dont know anyone who does. There is no SES or CEL light anymore. Annnnnnd when i pulled in my driveway i thought i would be funny and mess with my dogs so i went to give her some throttle and heard a pop from the engine bay. Thought it was back fire. But when i put it in park and gave it some revs i got nothing. I back down my drive and headed back up in the same mannor and nothing. Not sure what it was. I dont have a Catalytic converter (not that it would even have anything to do with it) Just not sure what would have made the sound. I check my plugs and they are fine. When going down the road and coming up on a hill i can put my pedal half way to the floor and still be losing speed. My engine doesnt gain rpm or anything just seems like its starving for fuel. I can hear the fuel pump kick on when i turn my key and i can hear the relay as well. Im just at a loss with no scanner.
 

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Discussion Starter · #21 ·
that TPS reading is perfect..

can you verify that each time it closes it reads the same..


did you see about stuffing a rag into the idle air bypass passage to block it.

then adjusting T15 idle stop screw to a very low idle speed... pull the shop towel back out and the idle will surge.. don't worry.. grap the throttle and take the RPMS to 1500 to 2000 and hold it stable there for 20 seconds.. then slowly return to idle.. that gives the computer the time to relearn the idle air position. you can shut it off.. wait 10 seconds and restart it without touching the gas..

this is a manual that covers both TBI and PFI for marine applications.. but it is the same testing for your preobd2 system. there is some there that does not cover your system. but a great idea.. in the first few pages . look at the CLEAR FLOOD mode.. that is why you need to have the TPS at the proper position and NOT vary..

http://www.weindex.info/pdf/FuelSystem/9.pdf
YEs, i can verify it is a solid .586 everytime it closes. About how many turns should i adjust the idle screw and can i access the IAC valve with it on the motor? I have never tried. I will do it tomorrow in the daylight since the world seems to think it has to get dark at 6:30. Should i leave it set at the lower idle or readjust back to "normal" i dont have a Tach so not sure what it idles at. But i do sometimes have to give it some throttle while its idling to get it to go into closed loop (idle lower like its supposed to) I dont know how many miles are on the motor since it isnt the original. Also when i took the TBI off i noticed the IAC doesnt sit flush, it is alway open a little, is it supposed to be?:confused::confused:
 

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Discussion Starter · #24 ·
Okay i dont what you said/what i read. Didnt seem to affect it any. The way it acts is almost like an injector is shutting off sometimes. Just boggs when i go to give it gas to go up a hill or even pick up speed. Only does this under load. Light acceleration its fine. If i punch the pedal it falls on its face. I am just going to have to assume for now its a Fuel pressure issue until i can get a gauge to put on it.
 

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Discussion Starter · #28 ·
The factory did not use a roller chain in flat tappet cammed engines and did not use a double row roller in roller tappet engines it was single row roller which does have a bit better life than the morse chain over a plastic tooth gear b ut not near the life of a double row roller chain.

Bogie
Fuel Relay on mine kicks on everytime but the pump itself only kicks on everyother time ( if i cycle the key and dont start the engine.) Doesnt matter if i do it right after the fuel pump kicks off or wait 2 minutes the second time only the relay kicks. Shouldnt the pump kick on everytime?
 

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Discussion Starter · #30 ·
My oil pressure gauge is normally maxed out will occasionally on a perfect day work intermittenly. So Oil pressure sender could actually be the root cause of this. I will check the relay tomorrow in the light and if it dies ill replace the Oil sending switch and go fromt there. Also another thought i had, if my Injector(s) are fouling out at Operating temp could that cause it? After it warms up i noticed today it has a slight miss. But only does it in closed loop at normal operating temp.
 

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Discussion Starter · #32 ·
Alright I'll have to check that. When it starts running poorly it almost sounds like a small exhaust leak. I don't have an exhaust leak is the issue. I'll check and let you know.
 
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