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350 TBI Pumping Way Too Much Fuel. Help

  
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350 TBI Pumping Way Too Much Fuel. Help

 
8995Chevyman 8995Chevyman
New User | Posts: 6 | Joined: 01/11
Posted: 01/19/11
02:39 PM

Hello Gentlemen Ive been working on my 95 1500 for 2 full days now and cant figure out why its pumping too much fuel. Got the computer on it and it says fuel pump relay and TPS. i changed out the fuel pump relay and didnt change a thing and it still jus DUMPING FUEL into the intake! the TPS is fairly brand new and of course i cant even get the motor to warm up to get correct readings. i also had to put #1 on TDC to see if it maybe jumped time. but the chain couldnt of slipped and the crows ft was still super tight and the dist. wasent goin nowhere. The TPS is on a 670 holley and i cant think how it can go out? i checked the fuel pressure regulator and its perfectly fine and pumpin 9-13 psi. i have a fairly new distributor with new plugs (well not anymore, there fouled out) and a fairly new ign. coil and a jet stage 2 chip. (i put all of these on at the same time bout a yr ago) and threw the wires are firing blue spark which i know is bout perfect. ive been reading threw the forums and i cant find anything relating to this topic or i have but i checked just about everything 02, vacuums, i cant figure it out. could it be the ECU/ECM? or could the jet chip maybe short the computer somewhere? i notice all you guys talk about it hypertech and superchips which i should of found this site a long time ago for little upgrades like this. The computer has been throwing only 2 codes and whenever i reset it nothing shows up (duh)and like i said it still wont fire. truck was running fine until i was slowing down to a light and it jus died out of nowhere! i tried starting it back in neutral but it wasent firing (it was cranking over jus not firing) whatso ever. Any clues would be greatly appreciated! thanks guys Smile also you would think if the 02 was doin its job it would lean it out but it jus not showin on the computer except on the diagnostic scan it says exhaust rich but not throwin the code for the o2 thanks again guys  

redneckjoe69 redneckjoe69
Addict | Posts: 2337 | Joined: 03/10
Posted: 01/19/11
03:18 PM

can't you adjust the tps without the motor running?  or am i thinking a tpi motor?  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 01/19/11
06:35 PM

there are a hand full of things that can make the fuel injectors spray tremendous amounts of fuel......

the coolant temp sensor... the one with the black and yellow wires... the sensor or the wiring harness to the sensor could be bad... it would tell the ECM that the coolant temp is at -20F  


it could also be the map sensor...   Manifold vacuum pressure..   this is a little black domino sized device .. hooked to the back of the throttle body...   it needs manifold vacuum to it...  


another think... i am taking that you have a factory small cap HEI...   can you pull the distributer cap and rotor...  shine a bright flash light down the distributer shaft.. look at top layer of the reluctor where there is a gap around the distributer shaft...  you can see the second layer just barely exposed.. if you see cracks..  you will probably need to replace the distributer...   when the magnet cracks.. and it does happen.. it creates secondary out of phase timing pulses which confuses the ecm electronic timing control...  this type of failure with the distributer usually does not cause the system to run rich...


so....

can you see the spray from the fuel injectors...   disconnect the electrical connector from just the injectors....

try to crank the motor....   while somebody watches the injector spray...  is fuel still flowing from the ends of the injectors with the power disconnected...  it SHOULD NOT be..      you might be able to even start the engine at this time... at least for a few seconds...  perhaps using some carb spray or brake cleaner to keep it running for a few seconds to clear the spark plugs....   this is with the injectors disconnected...    if the fuel pressure regulator is leaking.. you will still have to much fuel leaking into the intake...    does the fuel system maintain fuel pressure when the engine is off.. for 5 minutes or so...    if the fuel pressure regulator diaphragm is just starting to leak..   it will maintain proper fuel pressure.. but leak into the intake...


here is a chart of what the scan tool live data values should be... if you have a scan tool ...

Scandata  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 01/19/11
06:43 PM

with the injectors reconnected...   you can use a timing light.. hooked over one of the spark plug wires or the coil wire... to illuminate the cone shape spray...   you should have at idle... just a trickle... but in a nice shaped cone..


during cranking.. the injector pulse should be slow...

i have had fuel injectors short internally...   so when power is applied.. the spray will be intermittent or.. constant...

the power to the fuel injectors comes from the ignition switch.. through 2 fuses usually..   the ECM pulls the other side of the injector wiring to ground...

oh... by the way... how are the grounds...    why not stop what you are doing.. check the grounds...    there should be one on the thermostat housing.. or on a stud behind the thermostat housing.. take this off carefully and wire brush the ring terminal.. the bolt and the manifold where it attaches..    remember... electrons flow from negative to positive..  if you have loose grounds.. you may not have enough electrons to power the various circuits...

there are usually grounds to the back of the heads...   these get left off or loose a LOT...


the computer is ONLY grounded to the engine block the grounds to the front of the intake.. or to the back of the heads.. sometimes both..  but both grounds are important to check..,  

55Guy 55Guy
Guru | Posts: 895 | Joined: 08/07
Posted: 01/20/11
07:18 AM

Just because the TPS is fairly new doesn't mean it can't be bad. I've seen plenty of the cheaper replacement TPS sensors from parts stores go bad prematurely.

I've got a '92 TBI truck. first thign I'd suggest is swapping in a new TPs sensor and see what it does. If the computer still spits out a TPS trouble code, I'd be suspicious of the computer box being bad (Had that happen with my truck too). The computer isn't that expensive for the TBI trucks, so replacing it won't cost a fortune.  

8995Chevyman 8995Chevyman
New User | Posts: 6 | Joined: 01/11
Posted: 01/20/11
09:55 AM

Alright! Thank you guys ive got some work to do. O and waynep ill check everything that you listed and ive checked the grounds and wired brush all of them that i have found and tightend them they werent too loose. 55guy thanks for the input for the TPS ill be swapping it out after i check this huge list from waynep. Thank you guys i really appreciate it. ill let yall know whats goin on later thanks again  Smile  

8995Chevyman 8995Chevyman
New User | Posts: 6 | Joined: 01/11
Posted: 01/24/11
06:45 PM

Hello gentlemen well i finally got my 350 fired but barely idling around 400 rpm. i replaced the computer all my grounds, vacuums, waynep i checked everything you listed.And finally the scan chart shows up, ill check the scanner variables in the morning. but everytime we try to rev the motor barely it just dies. im thinkin the TPS might be bad. i have a friend say that the TPS can keep the truck from running rite. and i replaced the spark plugs and the oil. Tom mornin im switching that TPS out. i hope that works. ill let yall know if that fixes the problem. i also switched out the computer with the correct prom for the 350 TBI, since i use to have the 305 in it.  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 01/24/11
07:17 PM

there was on another forum...  a similar sets TPS code...   the owner changed the TPS...  i also said to change the TPS connector and pigtail... i guess he did not...  he finally took it to a professional shop... they changed the TPS connector...  fixed it...


Duralast/Connector - Throttle Position Sens
For your 1995 Chevrolet Truck C1500 1/2ton P/U 2WD 5.7L TBI 8cyl
Part Number: 417
this is a round body connector with 3 terminals in a triangle shape..  the earlier TPS sensors used 3 in a row...


copy and paste this link....

http://www.fastbird93.com/Diagnostics.htm

open the 4 pages of code 21 and 22  print those 4 pages...   changing the terminal is quicker.. and may fix the problem...   with those 4 pages... see if you can force a code 22 ...   erase that .. then force a code 21...

those 4 pages... will really help.... and yes.. some of the other stuff on that page is for the cars with optispark distributers..  but the rest is the same...  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 01/24/11
07:28 PM

curious... are you running the throttle body from the 305?????/  if so... you may have to reset the base idle speed to compensate for the larger displacement..


i would also like you to grab the throttle lever.. open it slightly.. see if it wobbles around in the shaft bore..  this can create problems of its own...  

so.. with a scan tool.. what's the TPS minimum voltage...    does it change when you slowly depress the accelerator.. KEY on .. engine off..  from 0.75 to about 4.5 at wide open throttle..

look also with the scan tool.. and the engine idling...  i like to see between 20 and 50 IAC.. idle air counts...

this is how many steps back the idle speed control motor is at..    if the engine is warmed and the idle air counts are not between 20 and 50 .. something is wrong...

how hot is the motor..    190F to 215F is a normal range for a belt driven fan blade gm motor..  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 01/24/11
07:35 PM

last thing... about the scan tool data chart above....

the order the info is displayed on various scan tools varies..

look at the first sensor read out on your scan tool....   find that matching line on the chart... write your data on the chart.. next to the proper line...

then go on to the next sensor in your scan tool....

looking at that chart...  will just overwhelm one..  i have to look at it one line at a time.. and i have been doing feed back carbs and these systems since 1981....  they actually started in 1979 on a few models...  feed back carb systems became throttle body injection.. became port fuel injector.. became sequential port fuel injection.. finally became OBD2...  

8995Chevyman 8995Chevyman
New User | Posts: 6 | Joined: 01/11
Posted: 01/28/11
09:39 AM

Hey guys finally got my truck fired up. Shes running better then before. the problems were The ECM- had a 5.0 blew it up and dropd a 5.7, the prom on the computer was for the 305-which at the time caused hesitation between 1500-2500 RPM. which is now gone. Waynep thanks for linkin me to http://www.fastbird93.com/Diagnostics.htm
I was testing the voltage on the MAP sensor and it was bad also.

Also when the truck fired up we couldnt get it to stay runnin it would fire up to 900 rpm for 2 secs then just die.  i was surprised, i had a friend thats a master mechanic finally come out to look at my truck. and my distributor was almost a yr old but the computer control advance went out in the distributor and the computer kept on trying to retard the distributor (I think that what happened) but it was under warranty thank you O'relieys ha but swapped it out now my truck runs like a dream.
Also i was curious i have a jet chip that ive had on the truck for a lil bit but kept gettin lil problems with it should i switch to a Hypertech chip,Superchips or should i stay with jet? i want your opinions? Thank you gentlemen for the helpful facts and tips on diagnoiseing these problems it saved me probably at least $1,000 for a shop to fix it, and that is a grand i dont have haha ive really appreciate yall helping me out thanks  

waynep7122 waynep7122
Guru | Posts: 1130 | Joined: 08/09
Posted: 01/28/11
10:27 AM

one last thing....

do you have the 305 throttle body on the motor.. or the correct 350 throttle body..

there is a difference in injector flow rates...


with 305 injectors on a 350.. it will run at speed just fine.. as the system can correct the fuel trim as it uses the oxygen sensors to set the fuel mixture..

but during acceleration...  the system drops out of closed loop operation where the adaptive programming is...

and back into open loop.. where everything is hard programmed...    with the 305 injectors on a 350... you will be too lean on acceleration ...  as the computer program is probably very similar in the fuel feed curve for the 5.7 computer. but it expects more fuel to be sprayed in by the larger injectors...

understand that..  its hard to comprehend...  but its the fact...  

8995Chevyman 8995Chevyman
New User | Posts: 6 | Joined: 01/11
Posted: 02/04/11
01:46 AM

hey wayne and no i replaced the old TBI with a pretty lookin holley 670cfm =)so what do yall think? chip the motor or let it be?