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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: lehman368 on May 23, 2019, 02:25:55 am
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It has a long cranking to start at least 4 seconds then fires up. You stop and shut off run in some where for 15-30 minutes it fires right up after turning the key. Is this normal with the early tbi models? Thanks for any help.
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No it's not normal. Check your fuel pressure, check for a leaking injector, ensure fuel pump energizes to full pressure with initial key on cycle.
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vile would this be symptomatic of a bad fuel pump relay?
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My cousins 90 does this. If he cycles the fuel pump twice before cranking it starts up pretty quick. Other than that it will crank for longer than it should. Runs great otherwise and it has a fairly new fuel pump as he thought that was the problem.
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1) First, i assume you mean sitting for hours, not the other thing that was typed....... ;)
i'm going to go with leaking injectors.
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No it's not normal. Check your fuel pressure, check for a leaking injector, ensure fuel pump energizes to full pressure with initial key on cycle.
I can cycle the key on and off a couple of times dose not seem to help. The throttle body was rebuilt with new fuel injections last year
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1) First, i assume you mean sitting for hours, not the other thing that was typed....... ;)
i'm going to go with leaking injectors.
The injectors was replaced just last year and tbi was all rebuilt.
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do you hear the fuel pump come one when you first turn the key on?
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do you hear the fuel pump come one when you first turn the key on?
It not real loud but I can hear what seams like a fuel pump it has duel tanks it’s the same on both fuel filter was changed also when we rebuilt the tbi. Each tank would have it own fuel pump correct.
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do you hear the fuel pump come one when you first turn the key on?
It not real loud but I can hear what seams like a fuel pump it has duel tanks it’s the same on both fuel filter was changed also when we rebuilt the tbi. Each tank would have it own fuel pump correct.
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Do you know if there is a check valve on the return line to fuel tank or where a check valve would be located at?
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no, theres no check valve. if you take the fuel cap off you should be able to hear the fuel pump for a few seconds when the key is first turned on.
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no, theres no check valve. if you take the fuel cap off you should be able to hear the fuel pump for a few seconds when the key is first turned on.
Ok I will check that thanks
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First of all it just a guessing game if you don't have a fuel pressure gauge on this. If you can get a hold of a gauge you can isolate the fuel pressure drop of either the supply side or the return side. If you cant get a hold of a gauge and see no external leaks or drips from the injectors it could be the pump check valve. But if does it on either tank its not likely. I know you said the TBI unit was rebuilt but my best guess would be the fuel pressure diaphragm seat. They are a highly polished seat that mates to the casting in the throttle body to close off the fuel return to the tank. If it is not seating good from say a burr it could be bleeding off.
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i was recently working on a tbi from the 88-98 style, pretty much the same setup. i installed a pressure gauge where the filter should be and installed two ball valves, one on each side. this way i could turn off each side to check to a check valve and there was none on either side, pressure bleed off from both sides. problem was either a poor ground or bad fuel. changed batteries and the issue slowly went away. but there was still no pressure being held, like there was no check valve
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First of all it just a guessing game if you don't have a fuel pressure gauge on this. If you can get a hold of a gauge you can isolate the fuel pressure drop of either the supply side or the return side. If you cant get a hold of a gauge and see no external leaks or drips from the injectors it could be the pump check valve. But if does it on either tank its not likely. I know you said the TBI unit was rebuilt but my best guess would be the fuel pressure diaphragm seat. They are a highly polished seat that mates to the casting in the throttle body to close off the fuel return to the tank. If it is not seating good from say a burr it could be bleeding off.
I working on getting a fuel pressure gage. I just got the 87 Series trucks service manual and drive ability books. Im seeing there are two types of fuel systems and where to put the the pressure gage by fuel filter. I’m been getting everything by one most of the other issues corrected but this long cranking issue has been around for 3 years as long as I have owned the truck. But I will get pressure gage and start there. I’m going on vacation tomorrow for a week so it will be a little bit before I get under the truck. Thanks for the information I will keep you All posted on what I find with fuel pump and pressure
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First of all it just a guessing game if you don't have a fuel pressure gauge on this. If you can get a hold of a gauge you can isolate the fuel pressure drop of either the supply side or the return side. If you cant get a hold of a gauge and see no external leaks or drips from the injectors it could be the pump check valve. But if does it on either tank its not likely. I know you said the TBI unit was rebuilt but my best guess would be the fuel pressure diaphragm seat. They are a highly polished seat that mates to the casting in the throttle body to close off the fuel return to the tank. If it is not seating good from say a burr it could be bleeding off.
Thanks
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for grins hook a jumper wire from battery to the 3" red wire on the fuel pump relay. this will bypass the ecm and energize the fuel pump. see how it starts and compare that to the noise you suspect is the fuel pump. this will energize the the fuel pump even with the key on
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for grins hook a jumper wire from battery to the 3" red wire on the fuel pump relay. this will bypass the ecm and energize the fuel pump. see how it starts and compare that to the noise you suspect is the fuel pump. this will energize the the fuel pump even with the key on
Go from the positive side of battery to the red jumper line
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for grins hook a jumper wire from battery to the 3" red wire on the fuel pump relay. this will bypass the ecm and energize the fuel pump. see how it starts and compare that to the noise you suspect is the fuel pump. this will energize the the fuel pump even with the key on
Go from the positive side of battery to the red jumper line
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I replaced the fuel pump relay Saturday. At first I thought it worked but after it set over night it still had long crank again
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I have to say that this is what if frustrating: no follow up and no results
Irish suggests bypassing power so you can listen to the pump to see if there is a difference. That is huge in analyzing what is going on!
Since you have changed the pump we will never know unless you try again.
Have you looked for tubing issues that may have blockage, creating a vacuum that the pump has to overcome?
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I have to say that this is what if frustrating: no follow up and no results
Irish suggests bypassing power so you can listen to the pump to see if there is a difference. That is huge in analyzing what is going on!
Since you have changed the pump we will never know unless you try again.
Have you looked for tubing issues that may have blockage, creating a vacuum that the pump has to overcome?
He I have responded I trying to find locate a fuel pressure gage. And I have replaced the fuel pump relay. I’m currently working 16 hours a day at my full time jobs and I have tried taking it to a garage to have them look at the issues they charge me $ 125- 200 and they tell me they can’t find anything. And I have same issues. I guess I have diagnose the problems my self and with the help of all of you Gus on here. Sorry I’m only lucky to have 4 hours a week to try to fix the issues. I want to drive it daily but hope it will start and I’m not doing more harm to it. I would love to have 10- 20 hours a week to just work the bugs out of it and to get it preforming the way it should and be able to take someone a ride. So they won’t say why is it dose it do that. but that won’t happen until the middle of July with my work schedule right now. I have looked at the fuel lines from tank to fire wall from what I can tell they look ok not soft not cracked. Looked at fuel lines going to Tbi when it was rebuilt. When I bought the truck i have a Friend that was a dam good mechanic 70’a 80’s 90’ vehicles. Then a little over year ago he was killed in car accident and I don’t have his knowledge and experience We put the engine and transmission back in the truck and had truck running great for over a year. It has always had that longer start issue he never got the chance to figure it out. And it truck also has a very slight bobble or could be miss at 35 mph to 50 when going the same speed in those ranges or letting up on the gas. It could seem as a Slight out of balance tire. But it is not I have two sets of tires and dose it on both set. I know it’s not tires. I just put 500 highway miles on it last weekend no other issues than the two. I do have GM service books now and going through them also. But have not come across anything yet to help.with the issues. Thanks for all of your time and help. Tom
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Here is something to check that i forgot about. The relay is activated by the ECM. If the relay fails then the oil pressure switch next to the distributor will bypass the relay and activate the fuel pump. If it takes a few seconds to build oil pressure then that will lead to the fuel pump not coming on which would be long crank time. Now I know you said you changed the relay but that is only part of the circuit. ECM may not be activating relay. You have a power side and a control side of the relay. Look on this site in the emission book. It has the schematic of the fuel pump and relay. Study it to gain the knowledge of how the system works.
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Sorry if I came across as a butt head, my observation is across the board, not just your issues.
On the tire issue, have you looked for a bent rim? Easy to miss.
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Sorry if I came across as a butt head, my observation is across the board, not just your issues.
On the tire issue, have you looked for a bent rim? Easy to miss.
No big deal just my frustrations also about this truck is a very nice truck and trying to make it run probably. I want to do other cosmetic things to the truck but I want it to run right first. But I will keep digging on it I will look at the oil pressure switch also and the way it works
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this is the schematic for the dual tank tbi
(http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=23791.0;attach=19852;image)