gmsracing

I've done a fair amount of research and searching, but I haven't been able to track this one down yet. Purchased a stock '86 951 a couple of months ago. Car was boosting properly to ~ 1.75 bar on the stock gauge. Now it will only hit 1.5-1.6. KLR is not in limp mode at 1.2 bar. Car wasn't idling properly, so I pressure tested the system and found a bunch of leaks using the soapy water method. I took off the intake manifold and fixed/replaced:

-New cycling valve. (leaking at the electrical connectors.)
-New ICV (leaking at the electrical connectors/side)
-Venturi delete added. (leaking)
-Epoxied manifold nipples. (leaking)
-Tightened a bunch of hose clamps. (leaking)
-New DME temp sensor--old was ok. Cheap to replace.
-Rebuilt throttle body--leaking at TPS. O-rings were trashed.
-New silicone hose vac lines where needed
-Banjo bolt was leaking--new crush washers
-New intake manifold gaskets-nasty
-Injectors rebuilt/resealed-previous owner
-Rebuilt AFM (Fixed the idle issue.) Potentiometer was grooved.
-DME/KLR?-was sent out and tested OK by previous owner.

So, car was boosting properly before I took it apart. The whole system is much tighter than it was before I got it. I've clamped off the line going to the wastegate and it will boost properly. So, mechanical stuff is fine. So, my thought process is that the only things that have changed are:

-Venturi delete? Can't see why that would cause a low boost issue.
-I replaced the vac line from the J-boot to the cycling valve with a smaller vac line supplied by Lindsey. This line is cut off under boost as the cycling valve diverts pressure to the wastegate? Or, does pressure still bleed through here? Maybe go back to OEM diameter?
-Cycling valve wiring is a little suspect--but it seems to be working.

I'd prefer to keep the system stock and not go to a MBC. Thus, trying to work with the cycling valve.

Thanks!

GPA951s

Make up A "T" electrical connector for your CV... Simple connectors 2 male and 2 female, just so you can run the wires into the cabin. Tie-Wrap a multimeter to the dash vents and watch the signal to the CV. If you suspect the wiring is sketchy you be able to see when / the CV actuates (after 1/2 throttle) you should see 12v... If your foot is to the floor and you don't see 12V then its the wiring. Sounds like you covered most of the bases... I've had a CV intermittent before.. you can also take that harness and hook it to the battery (no need for engine to be running) and test the CV by hearing the "Click" when you apply 12v. wiggle GENTLY the terminals coming out of the CV to make sure they are not intermittent. with 12 volt applied to the CV and you wiggle the wires it should not click... if it does then you have a bad CV.. 1.5 to 1.6 means you are getting boost but some of it is getting lost...
Another thing to check for is the Boost Hose connections, I know you have checked them but just because they don't leak in the static position doesn't mean that when you Load the Driveline and the engine "Twists" in the car that they don't leak at that point.. Hard Hoses are a dead giveaway. I had my intercooler pipes off last year on my street car when I was freshening the timing belt and Noticed and Tiny crack in the IC to TB hose and when I pushed on it from the inside out the crack opened up. The boost was never an issue BUT when I replaced it I was giving up some power holy cow.. what a difference.. Good luck!

gmsracing

Thanks-I'll look into the cycling valve connector. It didn't look great; but I thought if it was working, at least it was working so to speak.

I also replaced the intercooler to hardpipe boots. (2) Also the throttle body to hardpipe boot was replaced.

divil

Have you pressure tested the intake?



EDIT...oops sorry I see you already did that. I'll leave this post here anyway for anyone reading in future.

Jim O.

Leaky wastegate diaphragm?

Humboldtgrin

No that would create a high boost issue

gmsracing

I pulled in the intake manifold this weekend and replaced the cycling valve to j-boot hose with a larger ID hose. It now seems to boost properly--1.75 in 4th gear. Won't hit full boost in 1-3.

divil

Have you checked the blow off valve/diverter valve? The top port should hold pressure or vacuum. If that's leaking it's harder to build boost.

gmsracing

It is an aftermarket billet diverter valve, but I haven't checked it yet. Would hope it would build pressure a bit faster than in 4th gear.

fejjj

If you still have a cat, then you likely have a clogged one.

Chapman951

My car was boosting with a faulty diverter valve. Suck on the top nipple and see if you can breath into it and out of it. If you can breath freely through it, it's faulty.