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E6 350 Boost ?


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I have an 88 E6 350 4 valve in my RD688S and 17 lbs of boost seems very low to me ! Truck has very low milage and has NOT been turned up and timing is spec.... Anyway I was wondering if a max of 17lbs was normal for a stock 350, I have checked all the obvious stuff, fittings, hoses, clamps, pretty sure the intercooler isnt leaking, I am getting full throttle etc ! HELP ! Thanks, Todd.

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I have an 88 E6 350 4 valve in my RD688S and 17 lbs of boost seems very low to me ! Truck has very low milage and has NOT been turned up and timing is spec.... Anyway I was wondering if a max of 17lbs was normal for a stock 350, I have checked all the obvious stuff, fittings, hoses, clamps, pretty sure the intercooler isnt leaking, I am getting full throttle etc ! HELP ! Thanks, Todd.

1989 tune up specs call for 19-27 psi, should be about the same for 1988. Check the reversing relay and fittings on the intake manifold (that runs over to the puff limiter on the fuel pump) if it's still there.

"Mebbe I'm too ugly and stupid to give up!"

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Thank you rhasler for the reply.... Yup I have taken the reversing relay all apart, thread taped and doped all fittings and put all back together.... wierd thing I found is there seems to be no boost leaks when checking with gas leak solution (thick blue soapy water) but when I shut the truck off the rear half of the reversing relay is sometimes leaking by but I believe that back half is pressurized by air pressure and not boost ? Looks rebuildable as the back half is threaded on and a relay I have kicking around in a parts pile is all one unit and cannot be taken apart....Another note, I have a gas cock plumbed between the reversing relay and pump so I can turn the puffer on and off with the twist of a knob, truck will belch the exact same amount of black smoke leaving a stop light weather the puff limiter is on or off !!!???

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Thank you rhasler for the reply.... Yup I have taken the reversing relay all apart, thread taped and doped all fittings and put all back together.... wierd thing I found is there seems to be no boost leaks when checking with gas leak solution (thick blue soapy water) but when I shut the truck off the rear half of the reversing relay is sometimes leaking by but I believe that back half is pressurized by air pressure and not boost ? Looks rebuildable as the back half is threaded on and a relay I have kicking around in a parts pile is all one unit and cannot be taken apart....Another note, I have a gas cock plumbed between the reversing relay and pump so I can turn the puffer on and off with the twist of a knob, truck will belch the exact same amount of black smoke leaving a stop light weather the puff limiter is on or off !!!???

There are a few different reversing relays, and I forget what the difference was between them. They do bleed air from the brake system by design. It sounds like maybe the puff limiter is shimmed out too much with the same result as turning off the air to it.

"Mebbe I'm too ugly and stupid to give up!"

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There are a few different reversing relays, and I forget what the difference was between them. They do bleed air from the brake system by design. It sounds like maybe the puff limiter is shimmed out too much with the same result as turning off the air to it.

check your throtle linkage as well make sure its going full stroke and the stop is going full on.The reversing relay with the prefix ending in P10 works best for most engines.,simply remove the bimbo from the pump and try it with out it hooked up to confirm your problem!

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Thanks for the help guys.... Yup I am getting full throttle, like i said the truck has very low milage and last spring I went through all throttle linkage and shimmed any play I found with stainless washers and even replased the "gas pedal" lol.... Anyway even with the puffer issue resolved it should have no effect on my low boost issue.... Any other ideas ?

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You state you are "pretty sure" the charge air cooler is not leaking but have not verified. If it were me making the decision this would be positively ruled out before preceding further along with the boots and connectors in the induction system. It does sound like the fuel system has been ruled out already. Probably wouldn''t hurt to look at the turbocharger itself as suspect also. I'm assuming the air filter is clean?

Rob

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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Is your truck set up with a chassis mount charge air cooler or does it have a series charge air mounted on the engine? Being a 350 I think it should be CAC but I can't remember for sure. If it is CAC and has the bypass piping for cold start you might look there too.

"Mebbe I'm too ugly and stupid to give up!"

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Thanks for the help guys.... Yup I am getting full throttle, like i said the truck has very low milage and last spring I went through all throttle linkage and shimmed any play I found with stainless washers and even replased the "gas pedal" lol.... Anyway even with the puffer issue resolved it should have no effect on my low boost issue.... Any other ideas ?

Heres how it works.

You need fuel to make boost they go hand in hand!

remove the puff limit bimbo from the pump and try the truck with it out it!

If you have an issue with the after cooler boost leaks ect you should be laying down black smoke and the pyro if you have one will be climbing very fast to 1000 deg or higher.

Other signs of lack of air is the turbo and somr times the manifolds will have a blue look to them from being heated. to much fuel being burnt in the exhast.

if you have no black smoke from this point on you have a fuel supply issue! The pump requires no less than 15 - 20 psi UNDER LOAD to run corectly 25- 30 is best you need to determine what you have and what you don't have in order to sort this thru.

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Ok guys all good points... Rob, according to my restriction gauge, which does work, I have very little restriction under load at full throttle but Im sure it cant hurt to toss in a new filter... Rhasler, my truck is an 88 it is an air to air system... fjh, my truck will let a consistant belch of black smoke and clean right up as boost and rpm's rise just as any correctly running 350 I have ever driven, thats with the puffer turned on or off, seems to make NO difference... But I will try removing the puff limit bimbo if you think i need to try that, just not sure what a bimbo is unless you have recently spotted me dragging some local pig (bimbo) home from the bar.... I have no bluing anywhere and pyro never sees above 1150 BEFORE TURBO (I drilled and tapped manifold) which I know on my Duramax there is a 300 degree difference between before and after turbo readings... Think there is a lot of room to juice this thing up !!! And lastly fjh, where is the correct place and proceedure to measure pump pressure at ? Thanks again guys !

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Ok guys all good points... Rob, according to my restriction gauge, which does work, I have very little restriction under load at full throttle but Im sure it cant hurt to toss in a new filter... Rhasler, my truck is an 88 it is an air to air system... fjh, my truck will let a consistant belch of black smoke and clean right up as boost and rpm's rise just as any correctly running 350 I have ever driven, thats with the puffer turned on or off, seems to make NO difference... But I will try removing the puff limit bimbo if you think i need to try that, just not sure what a bimbo is unless you have recently spotted me dragging some local pig (bimbo) home from the bar.... I have no bluing anywhere and pyro never sees above 1150 BEFORE TURBO (I drilled and tapped manifold) which I know on my Duramax there is a 300 degree difference between before and after turbo readings... Think there is a lot of room to juice this thing up !!! And lastly fjh, where is the correct place and proceedure to measure pump pressure at ? Thanks again guys !

Tap a pressure gauge, line, and "T" into the line going from the secondary filter back into the pump.

"Mebbe I'm too ugly and stupid to give up!"

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My dad was trying to chase down a low boost situation too on his 88 Rd... He ran two boost gauges, one in the pipe after the turbo and one off the intake manifold. Allegedly there's supposed to be less than 2lbs difference (?)...his had 5lbs+...plugged up CAC.

While it may not leak per se, it could be something to look into.

Ever wonder how a blind person knows when to stop wiping?

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Tap a pressure gauge, line, and "T" into the line going from the secondary filter back into the pump.

AGREED!

Take the bimbo cyl out and drive it first one thing at a time!Your tackleing a lack of fuel issue by your description!

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Kool I have some things to explore today ! Now, If my fuel pressure is low can it be adjusted or is it simply a sign the pump is getting weak ? Ambac pump by the way... Also the engine tag calls for 18 degrees BTDC of initial timing, was wondering how far you suggest to safely bump it up for maxximum HP gain ? This will of course be after any other issues are resolved....

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Kool I have some things to explore today ! Now, If my fuel pressure is low can it be adjusted or is it simply a sign the pump is getting weak ? Ambac pump by the way... Also the engine tag calls for 18 degrees BTDC of initial timing, was wondering how far you suggest to safely bump it up for maxximum HP gain ? This will of course be after any other issues are resolved....

you could go as high as 24 but Im not sure of the gains or losses!

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Kool I have some things to explore today ! Now, If my fuel pressure is low can it be adjusted or is it simply a sign the pump is getting weak ? Ambac pump by the way... Also the engine tag calls for 18 degrees BTDC of initial timing, was wondering how far you suggest to safely bump it up for maxximum HP gain ? This will of course be after any other issues are resolved....

You are not checking the high pressure fuel coming out of the pump going to the injectors here, you're checking fuel supply pressure to the pump. If it is low there may be a problem with the tranfer pump, restricted lines, or something else.

you could go as high as 24 but Im not sure of the gains or losses!

Be careful with adjusting pump timing. I've seen guys that "knew" what they were doing that wrecked brand new reman engines (1 hour total run time) and turned the pistons in another one into the liquid type. These were out of time by quite a lot, in the case of the reman engine about 45 degrees, FJH is probably right with as far as you could safely go, but I wouldn't go too much past the factory spec. Check the tag on the pump and see what it says as far as timing. How exactly are you checking the pump to engine timing?

"Mebbe I'm too ugly and stupid to give up!"

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You are not checking the high pressure fuel coming out of the pump going to the injectors here, you're checking fuel supply pressure to the pump. If it is low there may be a problem with the tranfer pump, restricted lines, or something else.

Be careful with adjusting pump timing. I've seen guys that "knew" what they were doing that wrecked brand new reman engines (1 hour total run time) and turned the pistons in another one into the liquid type. These were out of time by quite a lot, in the case of the reman engine about 45 degrees, FJH is probably right with as far as you could safely go, but I wouldn't go too much past the factory spec. Check the tag on the pump and see what it says as far as timing. How exactly are you checking the pump to engine timing?

Agreed as well! I don't like messing with timing Unless I'm tring to rid my self of a problem IE blu retarded smelling smoke ect! I once installed a pump on a v8 It would not run properly at the prescribed timing 19 degrees!I ended up setting it to 24 the guy complained the truck had no power it was a dog the engine was rated as a 400 we sent the truck to the dyno it dynoed at 463 to the ground. The guy shut up and payed the dyno bill!:banana:

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Agreed as well! I don't like messing with timing Unless I'm tring to rid my self of a problem IE blu retarded smelling smoke ect! I once installed a pump on a v8 It would not run properly at the prescribed timing 19 degrees!I ended up setting it to 24 the guy complained the truck had no power it was a dog the engine was rated as a 400 we sent the truck to the dyno it dynoed at 463 to the ground. The guy shut up and payed the dyno bill!:banana:

Sounds like he had a case of buyer's remorse!

"Mebbe I'm too ugly and stupid to give up!"

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  • 2 weeks later...

Hey guys checking back in as I finally rigged up a pressure gauge and here is the results.... 14lbs at idle 650rpm, 1700rpm produces the highest reading @ 27lbs, pressure gradually drops off to 23lbs @ 2100rpm.... Is this normal ??? Oh and one other thing for any trying this proceedure. use a liquid filled gauge ! A dry gauge will NOT work !!!

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Hey guys checking back in as I finally rigged up a pressure gauge and here is the results.... 14lbs at idle 650rpm, 1700rpm produces the highest reading @ 27lbs, pressure gradually drops off to 23lbs @ 2100rpm.... Is this normal ??? Oh and one other thing for any trying this proceedure. use a liquid filled gauge ! A dry gauge will NOT work !!!

That is enough pressure but it should be done under a load.You are using more volumun of fuel under load and if a proble is there the pressure will drop off big time under a load.

glenn akers

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That is enough pressure but it should be done under a load.You are using more volumun of fuel under load and if a proble is there the pressure will drop off big time under a load.

If it maintains 23 with a full load on the engine and does not drop below 20 id say your good to go But by what your discribing the drop at 2100 does not sound good !I thinK you may have a restriction some where.to test this run a good known fuel line into a bucket of fuel directly to the red filter do your test again see if the same thing happends if the gauge still drops off put the hose directly into your clean pail of fuel from the transfer pump and try again.

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  • 1 year later...

Hey guys checking back in as I finally rigged up a pressure gauge and here is the results.... 14lbs at idle 650rpm, 1700rpm produces the highest reading @ 27lbs, pressure gradually drops off to 23lbs @ 2100rpm.... Is this normal ??? Oh and one other thing for any trying this proceedure. use a liquid filled gauge ! A dry gauge will NOT work !!!

Would an old mechanical oil pressure gauge work? If not where would I find a liquid filled gauge?

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