ihatebarkingdogs-
Thanks for the feedback. I’ve heard of the potential issue regarding plugged cats. But I found the last part of your post the most informative. I used to be under the impression that the rotten egg smell meant the cat was going bad.
with this suggestion, and other things I’ve noticed, it looks like I’ll be spending time under the car. (Oh yeah) I’ve had the car on jackstands once before and that was a long process. Can you recommend a better system for getting the car off the ground far enough to do work under it? I’ve seen ads for things like race ramps but wonder if they’re sturdy enough or provide enough space to really get under the car.

thanks again for the input👍

 

Use the jack points along the rocker panels.
jack it on the rear one, the whole side goes up.
then u can put jackstands front and rear.

i had two melted cats. True duals with H pipe.
no power.had cats cut out and test pipes put in, it’s a beast again.
idled fine. Just gutless.
timing set wrong can cause it to stumble and that big woofing sound.
so if you set the timing, uh you might have a harmonic balancer that the rubber is bad allowing the timing mark to move around.
get s bottle of white-out, paint a line from timing mark to the pulley. Start it up, go for a drive, start it several times.
then check your lines.
if they are moving apart, u need a balancer.

 

Interesting info about the harmonic balancer. I’ll give that a try. My year has pre-cats. Have been advised those are no bueno. Need to find a way to test exhaust flow. Also thinking to have compression check done.

Thanks for the feedback Coupeguy👍

 

Ok Corvette Gurus
Did a little testing. Thought I would share results and get your feedback.
I bought a multimeter and ohmed my injectors. Readings were between 16.1 to 16.6. Got a fuel pressure tester. This is where things got interesting.

I hooked the tester to the Schrader valve and turned the key to the on position. Pressure jumped to 39 psi but dropped to 34 psi in about three seconds. Then pressure slowly dropped from there to 21 psi over the next 15 minutes. Did the test twice with virtually identical results. After testing I pulled the FPR vacuum line. It was dry and I could only detect a VERY faint smell of fuel. Replaced FPR vacuum line, started car. Idle fuel pressure was 29 psi. Removed FPR vacuum line while running, pressure jumped to 36 psi. Revved engine in bursts and fuel pressure would go to 36 psi. But when I ran the engine up to about 2900 RPM and held it there fuel pressure dropped to 27 psi.

Thinking FPR is ok (dry, no real signs of fuel, pressure jumped when vac line removed). Was thinking to access fuel send and return lines at top of tank and do the clamp test.
What do gents think?

 

Wait, did I miss something or does the car run without starting fluid now ?

 

First thing I would do is to replace the injectors with Bosch III's. The original injectors are not E10 friendly and tended to short out. You can get a good cleaned and tested set for ~$130.

 

Good way to test cats is with an IR heat gun. A healthy cat increases in temperature between inlet and outlet because of the chemical reactions. A clogged cat is the opposite, temperature on outlet will be colder.

 

Patsgarage
You must have me mixed up with another rescue 87…..lol.
Quick update. When I got the car it started fine, idled fine, and revved well without load. Under load (driving) she would not rapidly rev/accelerate beyond 3000 RPM (bogging/popping). I replaced plugs, wires, cap, rotor, coil, O2 sensor, and fuel filter. Same symptoms still existed. So I joined the forum for help. Based on feedback I purchased a multimeter and fuel pressure tester to do testing instead of just replacing parts. Injectors ohmed within acceptable range (16.1-16.6). Fuel pressure testing showed fuel pressure dropping from 38 to 34 psi as soon as fuel pump shut off after pressurizing the rail. From that point pressure dropped slowly but steadily to 21 psi after about 15 minutes. (shouldn’t fuel pressure stay mid to high 30’s for first 10-15 min?) Pulled FPR vacuum line after first testing. No visible signs of fuel or obvious fuel smell. Replaced vacuum line, started engine with gauge attached. Fuel pressure at idle was 29 psi. Removed FPR vacuum line while running, fuel pressure jumped to 36 psi. Replaced FPR vacuum line and revved engine in short bursts, pressure would go up to 36 psi. Revved engine to 2900-3000 RPM and held it there. Instead of increasing fuel pressure dropped to 27 psi. 😳 Was looking to esteemed Forum members for next step suggestions.

 

jv9999-
Thinking I may do that regardless. When I ohm tested the injectors I noticed they look pretty old/beat up. Probably original set. Wire connectors for two injectors had no clip to hold them in. Two other injector connectors had something that looked like a homemade clip of some sort. Where can I get a set of Bosch lll for $130?
Really would like my next moves to cure no acceleration/performance issues. Then I can enjoy the car while continuing to restore her.

 

hornetball-
Good tip👍 Really looking for concise ways to direct my moves while ruling out potential causes of issues. Thanks for the feedback.

 

You are right, I got you confused with someone else.
Getting old sucks.
That fuel pressure is a little on the low side for my liking, since you already replaced the filter I would pull the pump out and take a look at the pickup.

 

YES DO CLAMP TEST. that will tell u injectors are stuck partially open.

your pressure is a tad low. possible old/plugged filter (ive never seen one so plugged it wouldnt allow engine to rev) or possible weak pump or plugged fuel strainer or otherwise obstructed.

dont let people spend ur money. keep doing the diagnosis. good job.

let us know how fuel leakdown test goes with clamps. 👍

 

Patsgarage-
I hear you about getting old 😂

Regarding your feedback looks like great (or grey) minds think alike. From everything I’ve read fuel pressure seemed low, leak down seemed a bit fast. Especially concerned that fuel pressure drops under prolonged acceleration. Ordered a replacement fuel sock for my tank. She arrived this evening. Can’t hurt to replace it and I’ll need it anyway if I end up replacing the fuel pump. Thanks for the feedback👍

 

VikingTrad3r-
I am enjoying learning how to diagnose because I learn more about my car. 🤔
I feel like your assessments may be pretty accurate. The fact that pressure started decreasing right away instead of maintaining for a while coupled with low fuel pressure at idle and under prolonged higher rpm was concerning to me. Thought immediate but slow fuel pressure loss was more likely leaky injectors than issue with fuel pump. Lack of pressure at idle and even more so at prolonged high RPMs made me think there is also an issue with fuel flow. Fuel filter was changed may be 500 miles ago. I bought a replacement fuel sock for the tank. Planning to replace fuel sock then do another fuel pressure check while doing the clamp test. Also have another forum member that lives in my area who has kindly volunteered to bring his scanner over Friday to help me diagnose. So many good people on this forum 👍😎

 

assuming O2 all operating properly, look for high blms if pump weak.

exhaust smell lean or rich?

 

VikingTrad3r-
O2 sensor was replaced fairly recently. Exhaust is def rich.
What is “blms”? Still learning all these acronyms…..lol. I assume it’s something we’ll see on the scanner?

 

obd1—-obd2
blm = long term fuel trim
int = short term fuel trim


If pump is weak, air fuel would be lean. computer will command longer injector open time to compensate (to add more fuel).

first see what happens with the fuel system leakdown test.

 

VikingTrad3r-
So an abnormal or elongated BLM coupled with low fuel pressure would reinforce diagnosis that fuel pump is malfunctioning, correct?
And leak down/clamp testing could confirm leaky injectors (cause of rich exhaust). May also indicate pump is weak because it’s leaky, correct?

Really appreciate your insight 👍

 

yes you are thinking correctly in your diagnosis.

the leakdown will be tell tale. post up results here.

through controlled testing of each component, you can diagnose.

when you are doing the fuel pressure leakdown test:

id.sending and return lines

clamp return line

have a helper clamp the sending line right after the key on pressurization event. this rules a leaky one way valve in the pump body allowing pressure backwards. if the return line is clamped, only way it loses pressure is perforation in lines or regulator, or injectors.

i use vice grips with black tape around teeth and a rag over the lines.

 

[QUOTE=VikingTrad3r;1604748830]yes you are thinking correctly in your diagnosis.

the leakdown will be tell tale. post up results here.

through controlled testing of each component, you can diagnose.

when you are doing the fuel pressure leakdown test:

id.sending and return lines

clamp return line

have a helper clamp the sending line right after the key on pressurization event. this rules a leaky one way valve in the pump body allowing pressure backwards. if the return line is clamped, only way it loses pressure is perforation in lines or regulator, or injectors.

i use vice grips with black tape around teeth and a rag over the lines.[/QUOTE

VikingTrad3r-
Roger that. And if pressure was steady until I unclamped send line, that points toward leaky pump?
Sounds like we may be dealing with a 2 fold issue (injectors and/or regulator and fuel pump). I need to get some vice grips and black tape. Will post update tomorrow evening. Thanks again 👍😎