Engine/Transmission (1994 - 1998) 97 12v with no power

[VAdieselman]

I working on a 12v that doesn't seem to have stock power. It has had a fuel filter, air filter, and oil change recently. I took apart the fuel overflow valve and the spring was only about 3/8 inch long, so I replaced the overflow valve. It seems to have better initial take off now, but it still doesn't have any power over about 20mph. The fuel solinoid appears to be working properly. I am worried about a possibly clogged cat. The truck has 198k on it. I want to test the fuel pressure, but it appears you have to have some sort of special adapter??? Is there a shraider vavle anywhere?





Any Ideas?

Thanks in advance



David Starr

 

[TSterken]

Sounds like to me like the lift pump is bad. Thats what i have ran in to in the past

 

[VAdieselman]

How can I check it for sure?

 

[TSterken]

the easiest way to check is to replace it. If you don't have any gauges.

 

[HoleshotHolset]

Since you have an old overflow valve (and one that can be taken apart easily... )...



You can drill the part of the overflow valve (where the bolt used to go) out and tap it with whatever size you need to test the fuel pressure. The easy way to 'check' for fuel delivery problems is to warm it up good and hot... and hold your foot on the floor in neutral and see if/when it pops, spits, etc.



They'll either pop/spit from bad fuel delivery (could be air in the system) or retarded timing... which brings up another point. The timing could be low... check it out. Do a search for checking the timing on a 2nd Gen 12-valve... it takes a while... but it's worth it.



A clogged cat could do it too... the cat on my '98 was clogged pretty bad... but it still ran okay.



Let us know how it turns out...



Matt

 

[VAdieselman]

Since you have an old overflow valve (and one that can be taken apart easily... )...



You can drill the part of the overflow valve (where the bolt used to go) out and tap it with whatever size you need to test the fuel pressure.

LOL I had the same idea. I just came in from doing that very thing. The high and low sides of the pump make the guage fluctuate rapidly, but it seems as though it's getting plenty of pressure. I am farily certain the new overflow valve made a difference, but I still don't think it has the power that it should. The more I think about it, I think that the cat must be clogged. Unless anyone has any ideas on how to check it without taking it off, i'm going to pull it off tomorrow and have a look. I'll let yall know what happins.



Thanks!



David Starr

 

[HoleshotHolset]

You could measure the exhaust back pressure... Weld a bung into the downpipe and see where it's at...



I don't have any ideas what you should see for numbers... but there shouldn't be too much pressure in the exhaust at all...



Matt

 

[VAdieselman]

Well I pulled of the cat and it doesn't appear to be clogged. I also drove the truck without the cat on it and there is no differnce in power. I don't know where to go from here. The turbo does have a very slight amount of up and down play, none in and out. I don't think it's enough to hider performance. What next?



David Starr

 

[VAdieselman]

The easy way to 'check' for fuel delivery problems is to warm it up good and hot... and hold your foot on the floor in neutral and see if/when it pops, spits, etc.

Oh yeah, I did try this and the truck revs up fine. No popping or sputtering.



Any Ideas??



Thanks,

David Starr

 

[bmoeller]

I would check to see if the plastic line (supplies boost pressure for the diaphram to work) going to AFC housing on the top rear of the fuel injection pump is pinched or cut somewhere. If it isn't seeing enough boost, it will cut back the fuel. The AFC (air/fuel control) controls how much fuel should be delivered based on the amount of boost. More boost = more fuel. It is to help prevent excessive smoke under power (That's easy to fix though. ).



AFC housing (note- The TST fitting is installed on the turbo on the '97s. The end in the picture w/the fitting faces the firewall when on the engine. )-



#ad

 

[The patriot]

Sorry if this has been posted already....but

Maybe the fuel sock on the suction in the fuel tank has some crap in it.

Pull a suction line and apply some air pressure (low pressure) to the line. Oh yea, remove the fill cap first. :{

This is supposed to blow out the accumulated dirt, etc. It;s only a temporary fix, but it will tell you if that's the problem.



Other than this all I can think of is timing.

Eric

 

[HoleshotHolset]

Have you checked to see where the plate is situated? Perhaps sliding it forward a little bit will yield the performance you're after...



I've driven quite a few bone stock 12-valves... and they do feel pretty lifeless compared to even a mildly 'adjusted' one... maybe it's just 'normal'?



Does it have a boost leak somewhere? Have you tried putting a boost gauge on it?



If it was low on timing or had fuel delivery issues... it should pop like a son of a gun at 3000rpm and no load...



Matt

 

[VAdieselman]

I would check to see if the plastic line (supplies boost pressure for the diaphram to work) going to AFC housing on the top rear of the fuel injection pump is pinched or cut somewhere.

THAT WAS IT :-laf :-laf :-laf

It was broken off right at the fitting on the intake manifold!





THANKS A MILLION !



David Starr

 

[HoleshotHolset]

bmoeller gets the prize! Good find, man! I'm glad you got it figured out...



Matt

 

[Jim Fulmer]

Give that man a Cigar... ... sometimes it real hard to arm chair troubleshoot on here but we some how get it done.



Jim

 

[bmoeller]

I don't smoke, but my truck does. Oo. Glad it was a simple fix.

 

[Joe G.]

FYI. If you have a CA truck with an EGR valve the same problem can occur because of soot plugging up the AFC. In that case, the hose may be ok.