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Need help with 5.0 tbi

Old 06-19-2019, 10:49 AM
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Default Need help with 5.0 tbi

Hi guys,

I just rebuild my volvo penta 5.0gi pefs v8 (TBI) with new pistons, new valves... etc and the problem is the engine dont have enough power and sometimes start good, sometimes dont start good and have explosion by intake (I think too fuel inside) and when it start idle is good (just sometimes do a vibration I dont know why).

spark plugs and cap distributor is new. I set ignition 8º btcd like workshop manual say and I try to move it for see if there are some error here but nothing. I did a fuel pressure test connecting fuel cell port and it show (running) 15 psi

When is running the engine go well untl 3000 rpm more or less but I can't go more rpm and in neutral it go well until 6000 rpm with good sound

Please is somebody can help me or give me advice about where I can start to check I will be very grateful

Thank you guys!
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Old 06-19-2019, 04:45 PM
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is the timing advancing? Fuel pressure steady? Plugs look normal? Throttle opening all the way?
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Old 06-19-2019, 05:59 PM
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That pressure sounds low, if it is the same TBI used on GM vehicles I think it should be in the 30's IIRC.
The GM TBI's had a pressure regulator in the TBI that would get weak and need changing.
They were not expensive and were easy to change.
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Old 06-20-2019, 12:10 AM
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Originally Posted by billinstuart View Post
is the timing advancing? Fuel pressure steady? Plugs look normal? Throttle opening all the way?
At first moment I was thinking that was timing advance but I was moving it and is not the problem, maybe I need adjust 2-3 degrees but finally i'm pretty sure the problem is not advance timing
plugs look normal and thottle opening all the way. I really don't know what happen!!

Thank you!

Originally Posted by Stim View Post
That pressure sounds low, if it is the same TBI used on GM vehicles I think it should be in the 30's IIRC.
The GM TBI's had a pressure regulator in the TBI that would get weak and need changing.
They were not expensive and were easy to change.
That pressure was check in port of fuell cells so maybe can be different of finally pressure (I dont know) but yes I only can think a fuel problem. I'm going to check pressure regulator

Thank you!

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Old 06-20-2019, 05:05 AM
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Originally Posted by JoeTe View Post
At first moment I was thinking that was timing advance but I was moving it and is not the problem, !
Huh?? Timing is set by using a procedure to short out the timing advance and set the static position of the distributor.

It should never backfire, ever. Backfiring is never caused by too much fuel. It should never vibrate either. Do you have the manual for that set-up?
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Old 06-20-2019, 06:18 AM
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Originally Posted by billinstuart View Post
Huh?? Timing is set by using a procedure to short out the timing advance and set the static position of the distributor.

It should never backfire, ever. Backfiring is never caused by too much fuel. It should never vibrate either. Do you have the manual for that set-up?
Hi, when I dissaembly the engine i marked the distribuitor position (workshop said it) and when I reassembly it I put balance wheel at 8º btcd (advance timing of manual) and my first mark matched so I think is double check

Backfire just some time when I try to start and it dont start right and i have to "play" with throttle to start it when the engine is already started never have backfire but dont have enough power and yes sometimes do a "vibration"

When I check the low fuel pressure (port in fuel cells) is 15 psi and manual say should be 10 psi. The high pressure I don't know where I can test if you can tell me where I can test will be great

thank you!
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Old 06-20-2019, 06:26 AM
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Originally Posted by JoeTe View Post
Hi, when I dissaembly the engine i marked the distribuitor position (workshop said it) and when I reassembly it I put balance wheel at 8º btcd (advance timing of manual) and my first mark matched so I think is double check

Backfire just some time when I try to start and it dont start right and i have to "play" with throttle to start it when the engine is already started never have backfire but dont have enough power and yes sometimes do a "vibration"

When I check the low fuel pressure (port in fuel cells) is 15 psi and manual say should be 10 psi. The high pressure I don't know where I can test if you can tell me where I can test will be great

thank you!
Timing must be accurately reset while running according to a procedure available from GM or Volvo. Then check to make sure the timing advances with rpm.
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Old 06-20-2019, 06:36 AM
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What is the oil pressure? What procedure did you use to adjust the lifters?
A quick compression test could quickly identify a problem with the base engine set up.
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Old 06-20-2019, 08:49 AM
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Originally Posted by billinstuart View Post
Timing must be accurately reset while running according to a procedure available from GM or Volvo. Then check to make sure the timing advances with rpm.
So If i dont reset with proper tool it dont will running good? Because before of set 8 degrees I was moving delco and I didn't found good power (sometimes better some times worst...)
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Old 06-20-2019, 08:55 AM
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Originally Posted by fishbum69 View Post
What is the oil pressure? What procedure did you use to adjust the lifters?
A quick compression test could quickly identify a problem with the base engine set up.

Oil pressure is good (i dont remember exactly) but is high like always was here not problem i'm sure.
About lifters i set zero lash and one turn like manual say.

I think a fuel problem or ignition problem anyways you are righ I'm should test compression so I will do it.
I was thinking the ignition was not the problem because I move delco al finally set up at 8 degrees like manual but I dont use any tool to set up so.. maybe I need reset digital advance or something similar.. really dont know

If somebody can tell me where i can do the high fuel pressure test I can check it too

Thank you guys your help is very appreciate because I'm really crazy with this problem after of spend a lot of money
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Old 06-20-2019, 08:58 AM
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As far as setting the base timing with a TBI small block, you have to disconnect the distributor from the computer (ECU)...yes it has one. This is done by disconnecting one of the wires from the distributor (unfortunately I can't remember which one...maybe go to 3rdgen.org and ask them or google it) and setting the base timing to 0 degrees (TDC) then hooking the ECU back up. The ECU then manages all the timing functions.

If the problem persists, check to ensure that the distributor isn't a tooth off. If that's not the problem, check to ensure that the cam is installed and timed correctly.
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Old 06-20-2019, 01:34 PM
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Originally Posted by Wingnutt View Post
As far as setting the base timing with a TBI small block, you have to disconnect the distributor from the computer (ECU)...yes it has one. This is done by disconnecting one of the wires from the distributor (unfortunately I can't remember which one...maybe go to 3rdgen.org and ask them or google it) and setting the base timing to 0 degrees (TDC) then hooking the ECU back up. The ECU then manages all the timing functions.

If the problem persists, check to ensure that the distributor isn't a tooth off. If that's not the problem, check to ensure that the cam is installed and timed correctly.
Hi I was reading and I think is different from car. Volvo Penta say that need "tool" that you unplug wire and plug a volvo penta tool (jump to pines and another one to 12v)

I will check

Thank you!
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Old 06-20-2019, 02:53 PM
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Pull 1 wire at a time out of the distributor (engine idling)..and notice how much the idle speed drops. No speed drop..dead cylinder. Forget mechanical compression test unless a cylinder is not doing its fair share, then check compression on that cylinder.
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Old 06-20-2019, 04:19 PM
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Are you sure it has adjustable valves?
I did a top end on a 90's 4.3 that the studs had a surface on them and you just torqued the nut/ball down.
I have adjusted a BUNCH of the older ones and it threw me for a loop.
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Old 06-20-2019, 07:43 PM
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Just in case....... have you triple-checked to make sure the plug cables are connected correctly and securely at both ends for the proper firing order? And the cables themselves are not arcing?( Check at night.)

If that engine has a 10-pin diagnostic connector, with engine running you could use a paper clip to to jump the B & C pins (as in step 5 in the link below) to hold the distributor in Timing Mode with no advance. Just remove when timing is completed to return to Run Mode.
https://www.google.com/search?q=timi...2G3nTX_ALDAsM:

Bill's suggestion for the power balance test above would quickly reveal dead or weak cylinders .

The 15 psi fuel pressure does sound low but i don't know what the spec for that TBI system should be.

Last edited by TTaxi; 06-20-2019 at 07:50 PM.
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Old 06-20-2019, 07:47 PM
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Not disagreeing with the importance of a correct base timing set. Looked at a 5.7 VP this morning (under 6 hrs on it) with 4 busted up pistons due to someone setting it with their ear. Ouch!
The intermittent explosion in the intake and vibration described and in the first post is more than likely not a base timing problem IMO. Low power and hard starting sure.
Have found excessively loose exhaust valve settings a couple times and even a faulty lifter to cause both of those symptoms. Just something else for the op to check. Would expect a compression test to pick up a problem there.
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Old 06-20-2019, 11:49 PM
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First I want to give you thank you guys a lot os people trying of help me so really is very appreciate for me. Thank you thank you guys!

Originally Posted by billinstuart View Post
Pull 1 wire at a time out of the distributor (engine idling)..and notice how much the idle speed drops. No speed drop..dead cylinder. Forget mechanical compression test unless a cylinder is not doing its fair share, then check compression on that cylinder.
All is new so hope that not problem... anyway I will check that and will test compression

Originally Posted by Stim View Post
Are you sure it has adjustable valves?
I did a top end on a 90's 4.3 that the studs had a surface on them and you just torqued the nut/ball down.
I have adjusted a BUNCH of the older ones and it threw me for a loop.
I set zero lash and one turn like manual said (if you referer that). So at first moment I think is good but anyways I will check compression test

Originally Posted by TTaxi View Post
Just in case....... have you triple-checked to make sure the plug cables are connected correctly and securely at both ends for the proper firing order? And the cables themselves are not arcing?( Check at night.)

If that engine has a 10-pin diagnostic connector, with engine running you could use a paper clip to to jump the B & C pins (as in step 5 in the link below) to hold the distributor in Timing Mode with no advance. Just remove when timing is completed to return to Run Mode.
https://www.google.com/search?q=timi...2G3nTX_ALDAsM:

Bill's suggestion for the power balance test above would quickly reveal dead or weak cylinders .

The 15 psi fuel pressure does sound low but i don't know what the spec for that TBI system should be.
plugs are connected right and firing order are right too I'm 100% sure. Cables and delco cap is new so here I think not problem. Spark plugs have 1 year and look good but anyway I order a new set so I will put new again to discart because I can think that sometimes vibration could be here although is strange for me but...is not a lot of money so i'm going to replace to new

Today I'm going to put a jumper for ignition mode and I wish that problem will be solved with that but if I don't understand bad doing that only "remove" ignition electronic advance for set timming with the gun (if you not do it your gun will read ignition base + ignition digital) so you cant set good ignition base because we can't know ignition digital but maybe i'm wrong and ecu need "reset" doing that but i'm sure that my delco right know is at 8 degrees like manual.

Originally Posted by fishbum69 View Post
Not disagreeing with the importance of a correct base timing set. Looked at a 5.7 VP this morning (under 6 hrs on it) with 4 busted up pistons due to someone setting it with their ear. Ouch!
The intermittent explosion in the intake and vibration described and in the first post is more than likely not a base timing problem IMO. Low power and hard starting sure.
Have found excessively loose exhaust valve settings a couple times and even a faulty lifter to cause both of those symptoms. Just something else for the op to check. Would expect a compression test to pick up a problem there.
the backfire is only sometines when I try to start the boat. Sometimes start good and sometimes don't want start and I have to "play" with throttle (and some backfire sometimes) and when it start never backfire and have good idle (just some vibration that is not normal).

Valves and valves lifters are all new

So today I'm going to jumper for ignition and test compression



THANK YOU SO MUCH!!
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Old 06-21-2019, 12:58 AM
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You need to put the engine in base timing mode. You can use a paper clip as shown in the link above. While in base mode, you need to set the timing with a timing light. There’s no getting around this.
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Old 06-21-2019, 06:37 AM
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Hi guys

I have news... If I retrase ignition engine start veery good (always) dont have enough power but have more power and almost dont have vibration

After I run engine and put in base timing mode and use timing light and I put at 8ºbtdc (that was same timing that i had without timing light) I removed the clip and turn off engine and start again and check with timing light to know what engine was doing with electric ignition working and Ignition was retarding from 8 degress so I tend to know that something arent right and engine cant advance ignition right...

Anyways if somebody can confirm that I right: Engine turn clockwise right? so 8º btdc degrees is at right of 0 º mark. (marks of flywheel) right?

I replaced mine knock sensor to a new one when i rebuild it. I replace it for Standart motor KS3 knock sensor (match with volvo penta and sierra part number) and I test ohms from new and old and was same... I dont think problem here but... more info for you guys

Thank you!
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Old 06-21-2019, 11:02 AM
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I'm reflexioning and I think I have a fuel problem and problem is high pressure pump.

If i set ignition timing 8 degress the engine start and run but not good and electrical ignition advance and retard coninually but If i put a 0 degress engine go better and electrical ignition advance until 8 degrees more or less and engine is better anyway dont have enough power. In neutral rpm are good but running in boat just go until 2600 rpm where best go and more power have is at +- 0 degress if I accelerate at full hardly engine have backfire i guess because ignition advance too much and dont have enough fuel to keep that ignition (and fuel is used as well to refrigerate for no knock)

So I tend to think that low pressure pump work good (15 psi) and is enough to run until 2600 more or less... and high pressure pump work but dont put enough pressure. I tried disconnect high pressure at idle and only a little bit more rough but pretty similar symphtons
And I was moving ignition retarding and advancing and I retarded ignition until idle is not stable and I advanced ignition until idle was rought and/or backfire and best position is 0 degrees although should be 8 degrees so really i dont think that we have here the problem I must have another problem (i tend to think fuel problem) that cause that my engine dont support correct ignition and of course dont have power

Fuel have as well 9 months or so I never had problem with that but like I dont have to much I refill with fresh fuel
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