ok yesterday i bought a 91 c-4 and upon acceleration it stumbles like crazy.Actually through out all speeds it stumbles.I changed plugs and wires and cap and rotor.I also put a fuel pressure gauge on it and it reads 50 lbs with key forward.I am thinking injectors.anybody have this problem before?also my tach is reading crazy...at idle it says it at 2,000 rpms but when you accelerate it jumps past redline.it seems to be off by 1000 at idle and 2-3000 during acceleration........any ideas on this?

 

what is your timing set at?

if you don't know how to check it, check the FAQ at the top of the page

 

Check oxygen sensor.

 

Just had injectors done, after exhausting everything else. How many miles are on it? Did you get any service records with it, or are you still in contact with the previous owner?

I can tell you from experience that whatever is wrong is fixable. Just requires knowlege and $$$s. How much of one directly affects how much of the other.

-Eric

 

THanks guys,,,,My timing was way OFF.I dont know who set it or what they thought they where doing but it wouldn't even read on the tab...it was way below actually....Runs like a million bucks now....thank god! Does anyboby have any idea about the tach?its still at 2,000 at idle and redlines at quarter throttle???????????

 

with hesitation, the first thing to check is always timing...

mainly because it's free

sorry, dunno about your tach though

 

The tach makes me think the filter is bad. The filter is a capacator thingy that evens out the pulse info from the distributor. It is a black cylinder near the distributor.

The stumble... hm... that is problematic. First off, the fuel pressure is way too high. Stock, with the vacuum line removed, should only be about 40psi. Recheck, if you had the line attached. Do you have access to a camera? If so, take a pic of the area around the rear of the fuel rail. That's where the Fuel presure regulator is, and if it's bad, it will do wierd things, I wonder if it's adjustable.

Other causes... bad coil. injectors. TPS.

Check the coolant level... if you have a leaking gasket, then a stumble will occur. There is a test available that will easily determine if there are combustion gases in the coolant. If they are present, you have a bad headgasket.

Another cause is a clogged catalytic converter. Take a rubber mallet and tap, sharp, but not hard, on the cat(s). If you hear rattles, then the cats monolith has failed, and the cats need replacing. If so, please look into high performance cats. They're not all that expensive, and will give performance. Depending on where you live, you can ditch the precats and go to town on the main cat only.

How to set timing - you need a timing light, no doubt. The process is simple: somewhere near the power brake booster is a tan wire. That must be disconnected. It has a connector. You need the 9/16" distributor wrench - go to sears for it. The bolt is on the passengers side, down low under the distributor. Loosen accordingly, but not too much.

the timing mark is on the drivers side, so is #1 cylinder. use that plug wire for the timing lights' inductive pickup. connect the light to the battery.

start the car, aiming the light at the timing mark (on the crank balancer) there is a scale, the bottom mark is 0, you want to move 2 high marks up (that should be 6* BTDC). You will have to phyiscally turn the distributor to change the timing. The mark on the crank is a little dot thingy, and it will move up and down against that scale. It's kinda neat, really.

I will check the timing cover on my gf's 87... and confirm the mark for 6*.

Shut off the engine, retorque the bolt and reconnect the tan wire.

What you have successfully done is set the base timing, the tan wire is what sends timing data from the ECU to the distributer.

Invest in a Helms manual - factory service manual - www.helminc.com

Keep us posted!

 

Does it have an adjustable fuel pressure regulator? 50 psi is too high for a stock regulator. Might not be an issue, I just thought that was strange if it is all OEM equipment.

(edit: looks like bogus beat me to it)

 

I agree... if that is stock, it's way broken.

 

ok well I already set my timing to 6* yesterday and that seemed to take care of most of the problem...it is a ajustable regulator and what is stock psi?.....also do you think i should just bypass that filter for my tach?also what can I take my timing up to (10-12*)......thanks guys...

 

ttt

 

Yes on the timing, get a new tach filter from the dealer, and set your fuel pressure to 44.

 

Is this the same on a 1990... I have the same problem....
Just looked at my engine... no black cylinder and a wire going straight to the firewall...

 

Still waiting...

 

i believe its identical on the 90's but one problem the dealer discontinued them.......I need to find some place that has it...any ideas?

 

try salvage yards (www.contemporarycorvettes.com; www.corvettesalvage.com; www.vette2vette.com).

or call Chris @ Superior Chevy, 1.800.728.8267. If he does not have it, he might be able to find it.

The Last Detail may have it, too.

 

thanks bogus,,i'll call tomarrow!

 

Superior won't be open, but the yards should be!

Contempory might be snowed in.

 

snowed in huh.....I haven't seen snow for 3 years..,...kinda miss it.......anyway thanks for the info and I will get it some how....sometime....,.thanks again