1987 GN won't rev past 4K RPM.

[Blackened87]

So recently I picked up a 87 GN and I had a issue where it would bog out above 5psi of boost. Well a new fuel filter solved that issue. Now it will build almost 15psi of boost but The engine goes flat at 4K rpm. No timing retard on the scanmaster and no popping or any abnormal noises, just gets to 15psi and don't do anything.
I changed the plugs, wires, module, and a new delco coil so I covered all the ignition stuff, I also replaced the fuel pressure regulator and the ECM since my scanmaster wasn't communicating. Normal driving around its fine and has plenty of power under 15psi, it's when I push it that it loads up and won't accelerate past 4K.
MAF counts are 7 at idle with the engine running. I was planning on unplugging it and see if I can push it harder. The engine has a little over 100K miles on it and most parts are original except what I just recently replaced.

Does this sound like a bad MAF, or a clogged cat or weak valve springs? I was planning on doing the valve springs next week, but I wonder if I have something else to check out as well.
Thanks for any info.

 

[dank GN]

Springs. There is many threads about this very issue .

 

[TurboBuRick]

Loads up? Probably starving for fuel. You did all that and no fuel pump and hot wire.

I have a wbo2 I throw in the tailpipe when I need to know.

Need data to really know what's going on. I bet your lean.

 

[Blackened87]

Loads up? Probably starving for fuel. You did all that and no fuel pump and hot wire.

I have a wbo2 I throw in the tailpipe when I need to know.

Need data to really know what's going on. I bet your lean.

I'm still getting the hang of the scanmaster readout. I don't really push the car until I get this sorted. I ordered the comp 980-12 springs, and just ordered the walboro pump and Hotwire kit from Gbodyparts.com.

I'm more then willing to invest into this car to maintain it and keep it running as it should so in only 3 weeks of ownership, I've already amassed a large amount of parts to install and get it running properly. The previous owner had the car sitting for a few years so I'm trying to get all the kinks out of it before I can really enjoy it.
I appreciate all the advice.

 

[MAK507]

My piece of crap GN does the same thing too. I realized TPS won't even go past 3.9 even when I do set it properly to read 4.5 engine off, ignition to on. I was assuming it was that causing it to not go up.

dank, what springs?



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[wb_7354]

Ok. 1st thing you said is that the new fuel filter helped. Later you say that the car has sat for a few years. Where did the car reside? Gas goes bad. If the fuel filter was bad I would be willing to bet the filter on the bottom of the fuel pump is bad too. The gas is probably no good that's in the tank. I would drain it. Clean it out. Install the new fuel pump. Change the "new " fuel filter. Your injectors could be fouled up with varnish too. Install your valve springs with the proper retainers. (Not the stock ones) check the cam lift on all cylinders while you're doing the springs. I would replace the timing gear set also. If it were me I would also buy a power logger and a wide band 02. If you get that far you should have a pretty good running car and always know what it's doing.


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[TurboBuRick]

I'm still getting the hang of the scanmaster readout. I don't really push the car until I get this sorted. I ordered the comp 980-12 springs, and just ordered the walboro pump and Hotwire kit from Gbodyparts.com.

I'm more then willing to invest into this car to maintain it and keep it running as it should so in only 3 weeks of ownership, I've already amassed a large amount of parts to install and get it running properly. The previous owner had the car sitting for a few years so I'm trying to get all the kinks out of it before I can really enjoy it.
I appreciate all the advice.

Sounds like you are on the right track.

The scanmaster "recall" feature is the best for seeing what wot throttle afr's are. After a wot pull, hit the "recall" button. Should read 780-800mv 0 knock. Hold "recall & mode" buttons to see the MPH it was recorded at. (Higher mv# = rich) (Lower mv# = lean)

I bet the fuel pump and hotwire will make a big difference.

 

[Blackened87]

Ok. 1st thing you said is that the new fuel filter helped. Later you say that the car has sat for a few years. Where did the car reside? Gas goes bad. If the fuel filter was bad I would be willing to bet the filter on the bottom of the fuel pump is bad too. The gas is probably no good that's in the tank. I would drain it. Clean it out. Install the new fuel pump. Change the "new " fuel filter. Your injectors could be fouled up with varnish too. Install your valve springs with the proper retainers. (Not the stock ones) check the cam lift on all cylinders while you're doing the springs. I would replace the timing gear set also. If it were me I would also buy a power logger and a wide band 02. If you get that far you should have a pretty good running car and always know what it's doing.


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The previous owner had the car sitting for a while, he decided to get it running so he drained the gas tank, put fresh gas and tried to start it. It ran like crap so he replaced all the fuel injectors with accell 30lb injectors and put new plugs and a coil on. It ran better but had a hesitation over 5psi of boost. After I replaced the fuel filter, it ran much better but the engine goes flat at higher boost at 4K RPM. No timing pull and the scanmaster is showing about 800 for the 02 under throttle, just the engine don't build power at that point.
I changed the plugs, delco coil and module, high output wires, TPS adjustment, denso 02, new coolant temp sensor, fuel filter, and cleaned the MAF.

The previous over had a aftermarket coil on it and gapped the plugs wrong. I didn't see any defects in the plugs but for my own piece of mind, I swapped them out. It's running great as long as I don't push it.
This week will be new valve springs and the fuel pump with Hotwire kit. Hopefully this will solve the drivability issue. It idles rather smooth and has great part throttle drivability. No hesitations and pulls very strong at lower boost and rpm.

 

[pacecarta]

i hate these threads
little info that dribbles in and lots of answers without the info

HOW MUCH BOOST DO YOU THINK YOU SHOULD BE ABLE TO RUN ON PUMP GAS STOCK IC STOCK PUMP AND WHO FRIKKIN KNOWS WHAT CHIP ??

15psi may be more boost than the chip can handle on pump gas stock ic
could be knock retard pulling the timing and boost down

and you want to unplug the maf and run it out hoping for better ..really?