Injector Help!

Hello guys. i have a few questions about injectors, are they hard to change in the series 1. Is there any write up for it. Also should i go back with stock, or is the any aftermarket injectors yall are using. I have done a few mod to my 95 like cat back exhaust, autolite 104s , res delete, Custom cold air intake with k&N, 180 thermo. The reason im asking is im have problems with my car at a low throttle response. At idle its fine but if i barely give it gas it studders and tries to die, but it if i mash the gas, WOT it performs fine. I have just replaced the plugs, wires, air filter, throttle body, fuel filter, and no help, same problem. It studderd before i did all this work . The injectors are the only thing i can think of. I have also run injector clean through them twice, no help. i run 93 octane. its been doing this for months, seems to be getting worse. Any advice would be much appreciated, thanks!

maggot wrote:

Hello guys. i have a few questions about injectors, are they hard to change in the series 1. Is there any write up for it. Also should i go back with stock, or is the any aftermarket injectors yall are using. I have done a few mod to my 95 like cat back exhaust, autolite 104s , res delete, Custom cold air intake with k&N, 180 thermo. The reason im asking is im have problems with my car at a low throttle response. At idle its fine but if i barely give it gas it studders and tries to die, but it if i mash the gas, WOT it performs fine. I have just replaced the plugs, wires, air filter, throttle body, fuel filter, and no help, same problem. It studderd before i did all this work . The injectors are the only thing i can think of. I have also run injector clean through them twice, no help. i run 93 octane. its been doing this for months, seems to be getting worse. Any advice would be much appreciated, thanks!

Do you have an SES light/codes? Could be a MAF sensor or fuel pump too.

any SES lights?

No SES lights and i cleaned the MAF when i changed the TB it looks fine

maggot wrote:

No SES lights and i cleaned the MAF when i changed the TB it looks fine

Check the fuel pressure...I'm not sure on the acceptable '95 specs so hopefully someone can chime in.

The reason i thought it could not be the fuel pump is b/c a friend of mine had a car and the the pump went bad, but at idle and light throttle no problem, but when he mashed the gas the pump couldnt keep up

maggot wrote:

The reason i thought it could not be the fuel pump is b/c a friend of mine had a car and the the pump went bad, but at idle and light throttle no problem, but when he mashed the gas the pump couldnt keep up

My fuel pump croaked and it stumbled/stalled at idle and part throttle. Never hurts to check, its free! (with the right tools)

what to i need to check it?

A fuel pressure tester, should be able to rent/buy one from your local Autozone etc.

thanks! hopefully someone will know what the pressure suppose to be

oh yeah, and my MPG sucks im avg 18-19 on a tank thats horrible for what i use to get. I get 350miles on a tank, i use to get over 400

maggot wrote:

oh yeah, and my MPG sucks im avg 18-19 on a tank thats horrible for what i use to get. I get 350miles on a tank, i use to get over 400

depends on your driving - Rivieras don't get great city/suburban mileage.

suggest that you Fix the apparent problems (fuel pump) then worry about optimization (gas mileage).

ok i just added the MPG in, i thought it might be a symptom, my driving habits are the same and im mostly hwy. I was just speaking on term of before the studder i had better mileage

The fuel pressure spec for '95 Riviera is 41-47 psi KOEO. When the engine is started, pressure should drop 3-10 psi and remain steady. Shut the car off, and monitor the fuel pressure on the gauge to see if it holds. If the pressure drops, you may have a leaky injector(s), or a bad Fuel Pressure Regulator. If you want to drive while checking the fuel pressure, you can route the gauge hose safely up to the windshield (close the hood), and tape the gauge on the windshield somewhere you can read it, without blocking your view.

I'm surprised it hasn't set an SES light if it runs that bad. I would have it scanned for codes if you can. Maybe the SES light is inop? It is possible that the MAF is skewed (as others have stated) causing the problem. I've seen it happen before without setting a code......

maggot wrote:

ok i just added the MPG in, i thought it might be a symptom, my driving habits are the same and im mostly hwy. I was just speaking on term of before the studder i had better mileage

Yeah, but in these large Texas cities, highway driving does not necessarily proceed at highway speeds, and if you're running faster than 70 mph or slower than 50, *or* if you are speeding up and slowing down, you're not likely going to exceed 24 MPG. Riv gets great mileage at steady hiway speed of 50, 55, 60, 65 MPH--it does not do so in hiway driving with speed changes. Why? I'd prefer that one of the mechanics on here explain it if you're interested, but the short story is that if you are changing speeds the PCM won't optimize the fuel trim et cetera for economy, rather it maps for power and power costs fuel.

That said, thorough maintenance will only help - if you have not done so, then clean injectors, inspect air filter (even if recently replaced) and replace if needed, strongly consider replacing oxygen sensors if you have over 100,000 miles on yours (actually, its best to test them with a scope because if things are clean chances are they *will not* need replaced even at higher mileage), and finally inspect and clean or replace the MAF and the throttle body (these require different and specific cleaners, DON"T just wash with carb cleaner you will kill them if you do). 999 times out of 1000 you don't need to replace either one, just clean them.

Here is a hint. Start the car and watch the tachometer. If the idle speed is not sitting rock steady - I mean if it moves a little bit, like +/- 25 RPM (the needle looks like it's shivering; if you have a scanner that will give you digital readout of the tach then you can read it direct) (I use Car Code) - if it is not rock steady then pull and clean the throttle body. You *might* need to clean or replace the injectors too, we'll see.

Albertj

Can anyone tell me the correct procedure for checking the fuel pressure on a 95? Where do I conncet the gauge? What do I do first. Just pretend I'm an idiot and start from the beginning. Lol thanks.

Should be a schrader valve on the rail somewhere? Looks something like this:

on the 95 sc, that valve looks the same, but is at the back of the engine bay on the fuel rail and sticks towards the back of the car.

I got my fuel guage at harbor freight for like $10. Works great for me cuz its not a guage you use alot but when you need one, you need one now.
But I am having a feeling that his problem is not going to be a fuel problem. I would bet on a EGR problem or possibly a O2 sensor acting funny. WOT shuts the EGR off. Almost as if its opening when the computer doesnt want it too or know its open, or possible that the EGR is stuck open

Thanks AA, thanks Karma you guys are always helpful. So just to make sure I have this straight, I attach the gauge to the valve, take a reading, put KOEO and take a reading, then start the car and take a reading, then disconnect a vacuum line from the fpr for a final reading. Correct? Thanks again guys.

I'm thinking EGR *should* report an SES. Any variation in the pintle position from what the computer expects would set a code.. I'd save EGR to last unless it sets a code, due to its price.

After fuel pressure checking, throw a volt meter set to measure resistance on the leads for the Throttle Position Sensor, slowly move the throttle through its range and look for any dead spots that don't linearly match up to you moving the throttle. Bad TPS can cause what you are describing. After that look into the o2, and see about pulling any codes, some don't set a SES light.

Got a scanner? looking at your fuel trims can also shed light onto whats going on.

edit: and yes, that process for checking fuel pressure is correct. If you do this and the gauge reads 0, you may have to remove the valve insert on the test port. I've heard of fuel pressure gauges that don't engage the valve to open it.

edit 2: and maggot, check your tube from the SC to the EGR for cracks(look under the flange where it connects to the sc), they ofter crack on the series one, and allow un metered air into the SC. This is more obvious in the idle and low throttle, less of an issue under WOT where you are getting more fuel.

Derek wrote:

Thanks AA, thanks Karma you guys are always helpful. So just to make sure I have this straight, I attach the gauge to the valve, take a reading, put KOEO and take a reading, then start the car and take a reading, then disconnect a vacuum line from the fpr for a final reading. Correct? Thanks again guys.

No. Attach the gauge, turn the ignition to the "run" position, take a reading (41-47psi). Then start the car. The pressure should be roughly 31-41psi with it running. Then shut the car off. The pressure should hold where it's at. If the fuel pressure drops, which could take some time, an injector or the FPR is leaking.

You also may also want to do what I did: buy a braided hose extension to allow taping the gauge to the windshield. You can then snake it through the cowl and watch/video fuel pressure while driving. Fyi, doing this will increase the price of your gauge by $30-50.

Here is my experience:

https://rivperformance.editboard.com/care-maintenance-f8/testing-fuel-pressure-spark-chasing-kr-t3352.htm

True. "Inexpensive" gauges have short hoses. Didn't think of that when I posted on the previous page. Just used to mine I guess. It's like 4' long.

Thanks for the correction Abaddon. I can always count on you guys for help.