ZRConekiller

Hey everyone so I had my 90 zr1 at a weekend long autocross event this weekend and charging out of the gate when relatively cold the car pulled strong all the way to 7200. Now after a few runs the car would come up to about 4000 rpm and it would fall on its face lack of power short shift the car and same thing. The weird part is that after I made the sweeping right hander the power was back and the car felt great for the rest of the run. Coolant temp was 98 degrees c so 208ish f. Anyone have any ideas? Yes all 16 injectors are original but we don't have any of the ethanol in or fuel you guys have in the states. I have another event coming up this weekend so any help would be greatly appreciated thanks.

ccmano

This must be going around.... it’s not injectors if it idles well, sounds like a clogged fuel filter or bad secondary fuel pump.
Check fuel pressure should be ~48-55 psi without vacuum to the regulator and ~38-45 with vacuum. I just did one with the same issue. Turned out to be the filter.

With the car cold, hook up a pressure gauge then simply turn on the ignition, don’t start the car. You should see 48-55 psi that way too. Another good way to test is to check the amp draw of the pumps. Good pumps draw 4-5 amps each, 8-10 amps when both pumps run. Less and your pumps are going bad. It’s nicely written up by Paul here...at post #7.

http://www.zr1.net/forum/showthread.php?p=136108
H

jay1055

Collapsing air intake duct ?

Rkreigh

the older air ducts suck closed. do a samco or put a coffee can in the stocker to keep it open

make sure the fuel pumps are good. easy way is to connect a fuel pressure gauge to the fuel rail shrader valve and tape it to the windshield.

if fuel pressure drops off check pumps.

check for sticky secondaries not openings and any codes

often injectors fail when hot, ask me how I know. warn the car up and you can ohm them out through the connnector harness without pulling the plenum

see zr1 specialist for a good write up on how to do this, it will save you a plenum pull

keep us posted and good luck

FYI

the FSM is the bomb for trouble shooting, I have a few spares for the early cars if needed. selling them for
$40

Paul Workman

One other thing...

When under hood temps were hot, my 1990 too would fall on it nose around 4000 rpm. Turned out to be the accordion hose between the air filter and the Throttle Body was collapsing.

I fashioned an aluminum sleeve that fits snugly inside that hose. Works like a charm! Marc Haibeck also provides some little wire hoops that fit inside of that tube that keep it from collapsing.

Either solution will prevent that hose from crushing at WOT/hot under hood conditions.

Rkreigh

we saw this clearly happening when we dyno the Z

ccmano

Certainly possible. I had it on mine early on. I built two hoops out of 1/8 welding rod similar to what Haibeck sells and installed them about 1/3 in from both ends. Problem solved.

http://www.zr1specialist.com/HAT%20W...ucts/hoops.htm

H

ucfchris84

I had a similar problem not the same.... Car would idle fine take off and anything past half throttle would fall on its face...... we swapped injectors and put some really nice all stainless injectors in and the car runs like a dream.. 90 zr1

ZRConekiller

Update I changed the fuel filter and I made a stainless steel sleeve for the intake hose. Had an event yesterday the car definitely worked a lot better thanks for the help. I still want to test the pumps and check several vacuum hoses.