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Username Post: desperate for help 1989 chevy tbi won't run        (Topic#218145)
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
05-31-09 03:15 PM - Post#1708286    

hello all, i have been reading posts on this site for the past month because my 1989 1 ton chevy (square body style still) with 5.7 tbi all of the sudden stalled out and now will not run. i can get it to start, but it will not accept any throttle and will just bog down and die. i have checked fuel pressure and get no reading from the actron gauge, although there is fuel flowing pretty well. all sensors have been replaced as well as the ecm. fuel pressure regulator has been replaced with fresh rebuilt one. if i unplug the vacum line from map sensor it will run pretty well but won't go down the road. i have checked egr, seems to be functioning properly. i did over heat the truck causing a blown head gasket and have had the heads off and back on with new gaskets. replaced timing gear and chain, timing was still correct. distributor timing is correct. i have dual tanks with pollak switching valve and have bypassed switching valve. both pumps come on with ignition and switch between tanks properly. my truck has been down now for 5 weeks and $650.00 please help.


 
LMC Truck
gchemist 
Senior Chevytalk Moderator
Posts: 22047
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
05-31-09 03:34 PM - Post#1708300    
    In response to motroo

Hello, welcome to the site.
Pull the codes on the ECM. You can find great TBI information on this site: http://www.cfm-tech.com/GM_tbi_tuning_tips.htm

Is the coolant sensor connected? Is the timing zero with the distributor disconnected?
Remove the air idle valve and clean it. The air idle valves need adjustment over time. The tip will distort and let air pass throught. Is the fuel filter old?

Do you have a vacuum gauge handy?
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS Ret. @236651 miles


 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
05-31-09 03:48 PM - Post#1708316    
    In response to gchemist

hi, thank you.
the coolant sensor is new and connected. timing has been set to zero with est wire disconnected. iac valve is new and has been reset. the fuel filter is new. no i do not have a vacum gauge. there were no codes on the ecm until i started pulling connectors to sensors. so no codes. i should add that i had a friend put his snap on mt2500 scanner on the truck and only found the codes to the est wire that we disconnected and the map sensor that we disconnected.

 
gchemist 
Senior Chevytalk Moderator
Posts: 22047
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
05-31-09 04:08 PM - Post#1708332    
    In response to motroo

Vacuum gauges work great to find simple problems. You can pick up one for $15 at most part stores.
http://www.secondchancegarage.com/public/186.cfm

I suspect a vacuum leak.
'83 Silverardo XST - ZZ4 powered
'96 GMC Jimmy LS Ret. @236651 miles


 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
05-31-09 04:34 PM - Post#1708348    
    In response to gchemist

ok, i will get a vac. gauge asap. what might i consider looking for with a vacuum leak? i did just pull the heads to have them resurfaced and checked for cracks, and put all new head, intake, exhaust, dist. timing cover, throttle body gaskets on. i also replace some worn out vacuum hoses that went to cruise control and other places on the back side. however, i did get the truck real hot a couple of times, enough to warp head and cause blown head gaskets.

 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15712

Loc: Colorado Springs, CO
Reg: 08-08-04
06-01-09 01:29 PM - Post#1708950    
    In response to motroo

When you unplug the MAP sensor, this makes the ECU think you are at wide open throttle - so it runs full rich on the injectors.

This means that either you have a massive vacuum leak - which is entirely possible given how much of the motor has been apart (resurfaced heads can cause problems with intake gasket sealing) or you have the PCV valve unhooked - OR - you have a fuel supply issue, even though you checked out and replaced the regulator, etc.

Look for a vacuum leak, and check fuel pressure at the TBI unit (you need to install a special fitting right at the tbi to read fuel pressure, get it at the parts store). It is one of those two.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-01-09 04:49 PM - Post#1709103    
    In response to motroo

  • motroo Said:
i have checked fuel pressure and get no reading from the actron gauge, although there is fuel flowing pretty well.

Find out why there is no pressure. If you tested it correctly, and there is no pressure, that is the problem.

Exactly how did you have the gauge hooked up, and where was it hooked up?

Did you test the pressure with the engine running?



  • motroo Said:
fuel pressure regulator has been replaced with fresh rebuilt one.

Just a new diaphragm or the whole regulator?

  • motroo Said:
if i unplug the vacum line from map sensor it will run pretty well but won't go down the road.



  • Vaughn Said:
When you unplug the MAP sensor, this makes the ECU think you are at wide open throttle - so it runs full rich on the injectors.

Yes, and when unplugging the MAP sensor helps the truck usually has a fuel supply problem.

  • Vaughn Said:
…………………… - OR - you have a fuel supply issue, even though you checked out and replaced the regulator, etc.

Look for a vacuum leak, and check fuel pressure at the TBI unit (you need to install a special fitting right at the tbi to read fuel pressure, get it at the parts store). It is one of those two.



Yes, the pressure must be tested with the engine running, and there is no test port.


For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-01-09 04:50 PM - Post#1709106    
    In response to Vaughn

ok, i rented a brand new actron fuel pressure test kit from autozone. i am not able to connect the adapter on the throttle body itself due to the egr valve and metal fuel line restrictions. i did hook it up right before the fuel filter. again this gauge does not indicate any kind of reading. if i depress the relief button, fuel will come out of the clear plastic hose but not at any kind of pressure. i wondered if the gauge might be defective so i blew 20 pounds of air pressure into the adapter and the gauge shot right up to 20 pounds, so i assume the gauge is in working order. ok, so then i blocked off the fuel return line, still no fuel pressure reading from the gauge, but there was a bit of pressure on the fuel return line. i have not had a chance yet to get a vac. gauge. so does it sound like really low fuel pressure? surely both fuel pumps did not go bad at the same time??? what about a wire shorting out somewhere for the fuel pump causing low voltage?? also, last night i took my throttle body apart to check all fuel ports for possible blockage, i did find on the inlet side that a little plastic seal had been broken and was blocking about a third of the opening, i checked all the rest of the ports and all looked good, reassembled and still no change. as far as a vacuum leak being a result of the engine being tore down, this problem did exist exactly the same before having the heads done and head gaskets replaced. but i will check for leaks.

 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-01-09 04:57 PM - Post#1709111    
    In response to motroo

hey chevyteck,
test was done right before the fuel filter with truck running although the only way i can get it to run is with map sensor unplugged. i replaced just the diaphragm but in 2 different regulators. 2 new diaphragms, in 2 used regulators. my original regulator and one i got off of a tbi 454. also i am currently using the injectors from same 454 tbi unit. unit was on a 3/4 ton suburban.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-01-09 05:02 PM - Post#1709118    
    In response to motroo

The switching valve for the dual tanks may not be switching from one tank to the other, and it could have one bad pump.

The switching valve could be stuck between one tank and the other tank.

Don’t worry about a vacuum gauge. The problem is no fuel pressure.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-01-09 05:09 PM - Post#1709125    
    In response to motroo

  • motroo Said:
hey chevyteck,
test was done right before the fuel filter with truck running although the only way i can get it to run is with map sensor unplugged. i replaced just the diaphragm but in 2 different regulators. 2 new diaphragms, in 2 used regulators. my original regulator and one i got off of a tbi 454. also i am currently using the injectors from same 454 tbi unit. unit was on a 3/4 ton suburban.



The 1994 and newer big block TBIs run at a higher pressure,26-32psi. The regulator is different. The injectors are different.

The TBI fuel pressure specification for small block Chevy’s is 9 – 13 PSI with the truck running.

Different size engines use different size injectors.
Once you get the fuel pressure problem solved the 454 injectors will be a problem.

What year are the 454 injectors for?
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


Edited by Chevytech on 06-01-09 05:12 PM. Reason for edit: No reason given.

 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-01-09 05:17 PM - Post#1709132    
    In response to Chevytech

ok, so i will put the original regulator back on and original injectors back on as i do not know the year of the 454 injectors. as far as the switching valve goes, it did switch between tanks as i got a face full of gas while checking it. and i currently have the switching valve off the truck and running on the left side tank directly. i ran the right tank out of gas trying to figure this out.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-01-09 05:26 PM - Post#1709140    
    In response to motroo

Well, if you have bypassed the switching valve and have it connected directly to the tank, and there is no pressure, and you are sure you had the return pinched off, then it is time to look in the tank.

The short hose connecting the pump to the sending unit could be leaking all the pressure into the tank, or the pump could be bad.

I do not recommend installing aftermarket pumps because of their high failure rate from past experience.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-01-09 05:38 PM - Post#1709147    
    In response to Chevytech

ok, but i have 2 tanks, with same situation on both tanks. is it possible for both tanks/pumps to fail at same time? i know anything is possible but how likely?

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-01-09 05:49 PM - Post#1709156    
    In response to motroo

I find it very unlikely that both pumps failed at the same time.

Double check your work on bypassing the switching valve and make sure you did not confuse a return line with a supply line.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
Cmartinjr 
Member
Posts: 231

Reg: 11-16-03
06-01-09 06:22 PM - Post#1709179    
    In response to Chevytech

well you ruled out fuel filter being problem. I'm inclined to agree that two fuel pumps failing is unlikely, wondering if there's a bad ground... maybe through fuel pump relay. lowered voltage to pump could affect its performance. Since I have no direct experience in electric pumps or dual tanks, most of this is speculation. if the control system for the tank and fuel delivery system switches all systems, then an electrical failure in an upstream system, would affect both tanks identically.
proud owner of a piece of junk
1984 Chevy G-10 van, complete with I-6 250 V-8 305 and 3 on the floor.


 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-02-09 04:01 AM - Post#1709355    
    In response to Cmartinjr

yes i too have considered a problem with voltage. chevyteck said it's time to drop the tanks which i think is a good idea, i might as well get everything checked and up to par, plus i would have to drop them to check the wiring 100% anyway. i have checked voltage going to fuel pump relay at over 12 volts, but haven't figured out which wire goes to fuel pumps. i did find a hot wire down by the switching valve and fuel tank area and it only had a little over 8 volts, it also had a splice in it i am going to look at that a little more too. right now i am just going to follow the instructions these guys are giving me because they know the process and step by step this thing will get fixed.

 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-02-09 04:15 AM - Post#1709366    
    In response to motroo

i would like to add also that i unplugged the fuel pump relay and the truck still started the same. i don't know if that is normal or not.

 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15712

Loc: Colorado Springs, CO
Reg: 08-08-04
06-02-09 12:50 PM - Post#1709657    
    In response to motroo

Truck shouldn't start at all with the relay unplugged. There might be some bleed-thru voltage from the control circuit causing the pump to run a little bit, which might explain it - but only if the relay is still plugged in.

A relay is an electrically activated high power electrical switch. This allows an ECU that only puts out a 12 volt signal with low current to control a high-power electrical switch remotely - and the fuel pump is a high current device. SO, if you want to test whether a relay is failed, you want to connect the two "thick" power wires together on the relay - this will hard wire the relay in the on position, and make the pump run all the time (you should be able to hear it when you connect it up).

To put it another way (using a bosch style relay) - If you want to "jump" the relay, connect the 30 terminal with the 87 (not the 87a terminal) to hard wire the pump in the on position. Doing this, then trying to start the motor - will tell you whether the relay connection has failed or not. If it runs, replace the relay. IF it doesn't run, it is time to take the fuel tank out.

By the way - when you "jumped" the tank selector switch - you have to jump all THREE lines - the supply (big), the return (medium) and vapor return (small). If you don't do this, the truck will not run well - and it will drain the supply tank early and pump it into the bypassed tank.

IF you pull the in-tank pump out of the the tank(s) - BE ABSOLUTELY CERTAIN TO MARK THE WIRES TO THE PUMP. There are no markings on either the pump or the wires, and if you hook them up wrong on the new pump it will run in reverse - and it probably won't start at all. Don't dismiss this part, it is very important that you do it.

 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-02-09 02:19 PM - Post#1709723    
    In response to Vaughn

ok, truck shouldn't start at all with relay unplugged, but it does. could this be an indication of a wiring situation ie. short or grounding somewhere? and as far as jumping the tank selector valve i'm not sure if i understand. i removed the valve and have spliced together the fuel supply and fuel return. i didn't know what the fuel vapor line was, and having said that, i have not cleaned this line out as i did the others. is this something i should consider? if this line became clogged, could it cause a problem?

 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-02-09 05:01 PM - Post#1709856    
    In response to motroo

ok, here is an update. i have reinstalled my original regulator and injectors, (i had replaced them with a regulator and injectors from a 454 tbi unit). truck is running about 50% better. i could probably limp it down the road if i had to. i rechecked the fuel pressure, still no reading on the gauge, but, this time there was no fuel pressure coming from the fuel return line as there was when i checked it with the 454 stuff on. is this significant? well now i too am convinced this is a low fuel pressure problem, but why? what wires can i check off the fuel pump relay to see if i am getting sufficient voltage back to the pumps?

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-02-09 05:02 PM - Post#1709860    
    In response to motroo

  • motroo Said:
ok, truck shouldn't start at all with relay unplugged, but it does.



When the engine has oil pressure a redundant circuit supplies power to the fuel pump. This circuit goes through an oil pressure sensor/switch. This circuit is independent of the fuel pump relay.

If you remove the fuel pump relay, the engine will have to crank until it gets oil pressure, and then the fuel pump will get power.

Once the engine has oil pressure the fuel pump should get power even if the relay has failed.



Does it have to be cranked a bit before it gets fuel pressure when you have the relay disconnected?
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-02-09 05:14 PM - Post#1709871    
    In response to Chevytech

yes it did have to crank more than normal

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-03-09 06:18 AM - Post#1710185    
    In response to motroo

  • motroo Said:
yes it did have to crank more than normal



Then it is probably cranking until it get oil pressure and there is not a problem.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
Vaughn 
"13th Year" Gold Supporting Member
Posts: 15712

Loc: Colorado Springs, CO
Reg: 08-08-04
06-03-09 01:24 PM - Post#1710427    
    In response to Chevytech

That contact on the oil pressure switch may be degraded some, because it sounds like it has been running on it for a while. It may be best to replace the relay (and check that the pumps kick on for three seconds when you turn the key to on but don't start the motor).

This may cure your low fuel pressure problems, but you may have to replace the oil pressure sensor/switch in the future, to make sure that if the relay goes out again - that you have a backup way to get it running.

 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3071

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
06-03-09 02:50 PM - Post#1710472    
    In response to motroo

  • motroo Said:
……………… what wires can i check off the fuel pump relay to see if i am getting sufficient voltage back to the pumps?




I think on that old of TBI truck, the fuel pump feed wire is light brown with a white stripe (tracer).

Don’t over look a ground problem, or wiring connection problems after the fuel relay.
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-03-09 05:22 PM - Post#1710557    
    In response to Chevytech

installed new fuel pump relay today, no help. will be checking wiring this weekend.

 
chevee55 
"8th Year" Silver Supporting Member
Posts: 453
chevee55
Loc: Oshkosh, WI
Reg: 09-05-03
06-04-09 05:34 PM - Post#1711275    
    In response to motroo

I had similar issues with a '94 truck and did many of the same trouble-shooting steps you did. It took a while before I noticed that I had a burned/bad ground cable from the engine block to the firewall. I replaced it and the truck ran perfectly... as it should, since it just had an ultimate tune up right before!
Good luck!

I want to add that I too, thought it was not getting enough fuel, since it would idle OK, but not rev up. I could limp it down the road, but it would stumble and hiccup badly. I too, replaced the fuel pump and sender after low pressure and voltage readings. That ground cable affected EVERYTHING! The tip-off came when I could "kill it" by turning on the headlights... too much electrical drain I guess caused the pump to die out??
Trevor


Edited by chevee55 on 06-04-09 05:39 PM. Reason for edit: No reason given.

 
motroo 
Forum Newbie
Posts: 50

Reg: 05-29-09
06-04-09 05:54 PM - Post#1711286    
    In response to chevee55

chevee55
thanks, i will check it out. having just had the heads off i remember having to disconnect that ground and putting it back on and didn't see anything unusual, but i'll check it out anyway.
thanks

 
Bill K.b 
Senior Member
Posts: 4283

Loc: upstate NY
Reg: 10-24-05
06-06-09 01:28 AM - Post#1711925    
    In response to motroo

Take it off again and clean up both ends and everything it touches? Then make sure it's tight?

I've had no-crank situations where there was enough dirt or it was loose where you rotated the cable or wire around the lug and it would contact good enough you could start the car again.
Those who can, do. Those who can't, criticize it on the internet.

1988 G20 van 5.7L - driver.
1993 3500 dually 5.7L NV4500 - tow truck
1991 G20 van - parts truck

Plus cars for swap and sale
&yes, I once tried a frame swap on a 51 Chevy.


 
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