I am quickly losing fuel pressure from 45psi to ~18psi~ all within 3-4 minutes of engine shut down.

How do you determine if injectors are bad?
How do you test the sensor(s) associated with the cold start injector and/or primary cooling fan(since an electric fan will always run while motor is running when I tried installing one even when the engine is cold)?
How can a person eliminate the cold start injector without spending money?
Is there a good way to test the CSI to see if it is causing fuel leakage?

 

I had a problem with my 305, and it turned out the PO butchered all the Fuel injector wires, fuel pump wires and cooling fan wires.

After setting it back up to stock I found out why--

The PO was an idiot, couldn't figure out why there wasn't alot of pressure coming out of the injectors and rewired everything trying to get it to work. When it didn't work well, he sold it as a functioning motor (which I test drove for 30 mins).

After rewiring correctly, the Computer had actually gone bad and was givign weird signals. 87 bucks and a Refurbed New Comp later from NAPA and it runs well. Just been too lazy to rewire the Cooling Fan.

 

Thanks for the reply ScFlaCamaro.
I actually had a LONG explanation to what I have going on, but after a while I figured people may just avoid this thread because of that so I trimmed it WAY down hoping to lure out some info.

I have reconditioned injectors which are supposed to be flow-matched and cleaned/etc/etc/etc but I have a feeling that one has failed because of my fuel pressure issue and hard cold starts.

I have read several threads on here, but most of them aren't any help because I can't weed out the reliable information from other people's guessing

Hopefully someone will feel like answering at least a couple of the questions I posted without throwing the typical "try doing a search" answer, because I've already wasted 1/2 a day with that approach.

 

Have you tried doing a search?

J/k.

I'm by no means a mechanic or anything, but could your fuel filter be clogged? If you've replaced the injectors then there's no reason to think they've gone bad already.

Or it could be the computer. Good luck, and I'm sorry I can't be of much more help.

 

The filter is new(er). I put it on same time as injectors. I am definately losing fuel pressure fast after shut down and I'm pretty sure it is at the motor. I don't think the computer has anything to do with this issue.
Thanks for taking the time to suggest something though

I am hoping someone will tell me what they would do to eliminate things for now by testing/etc/etc.

 

Have you looked at or changed your fuel pressure regulator?

Fuel injectors are easy to remove.... bring them to a shop to have them checked.
I'm not sure that there's a way for a shade tree mechanic to check his own injectors for leakdown....

By the way, Fuel systems drop pressure once the pump stops..... why are you worried about it?

 

From what I have read on here, it isn't normal to drop 30lbs in 3 minutes after shut down so who knows.
That is why I figured I'd ask here.
My engine has developed a definite miss at idle and it has been hard to start when cold for as long as I remember.

I am somewhat mechanical competent and not a millionaire, so I'm not going to pay a shop to do something I could do on my own.

All I need is a little direction on what/how to test, that is why I figured I'd ask in a TPI forum.

 

Pressure can drop because;
check valve at pump is faulty
reg is leaking
injectors are leaking
CSI is leaking
the last two should give a obvious rich condition on startup ; smoke
To test ;
run pump to build pressure , clamp return line turn off pump and see if pressure holds.If it does ,reg is faulty
Do same on supply line; if pressure holds then check valve faulty.If neither has any effect then injector / CSI problem

Obviously have a fault somewhere,.If fan runs full time on your car A/c pressure switch may be faulty ( is it connected ? ) turning on fan full time

Switch at front of intake turns on CSI ( only has power to switch when cranking )
CSI can be deleted simply by removing the line from fuel rail to CSI and capping rail off ; leaving injector in intake to plug the hole unless you want to spend $30+ for the delete kit

 

It's normal for the fuel pressure to bleed back into the tank, some cars do it faster than others, it does this to relieve stress on the system when it's not running, otherwise there would be no need to prime it.
Put a fuel pressure gage on it and monitor it while it is running, if the fuel pressure stays constant you probably have nothing to worry about.

 

Wrong on both counts;neither has anything to do with his problem

 

Thanks guys for the replies.
I actually installed this TPI system on the L69 motor in my 87 monte carlo ss. I didn't want to say this at first because I knew people may not be able to accept that it was installrd properly and would concentrate on offering info towards things that have nothing to do with what is causing my problem. I say this because I had a perfect running car after the install up until about 1 month ago when I noticed this mysterious but definite miss at idle that has developed.
I also have what acts like a cold blooded carb engine when it's cold only. It has to be cranked for 5-7 seconds, then I stop, turn key forward to prime pump once again and it will then fire right up. If the motor is warm such as running into a store and coming back out, then it also fires right up no problem.
I may just eliminate the CSI just because it 'may' be leaking and I don't know why I was so persistent in installing it anyways when I did this swap. It is old, and I've heard people mention how they are problematic anyways.
What can a person use to block off the rail? It doesn't seem to be a common pipe plug thread? (I'm sure it isn't just to be difficult anyways).

I put a brand new AC Delco fuel pump in during TPI install, new fuel filter, and reconditioned injectors that were supposedly flow matched, etc/etc.
All of this has roughly 4,000 miles on it, and the first 3,500 were with a smooth running engine.
I spent an entire winter going over the wire harness and cleaning it up. so I'm fair confident the harness is fine. I do have an obvious fan problem, but right now I am still running a mechanical clutch fan. I did hook up the electric fan before, and although it worked as I thought it should with A&B jumpered, it must have some issue since it shouldn't just run constant when motor is cold and running. I tried linking this to my other problem wondering if it had anything to do with the car just thinking it is hot when it ain't(CSI wouldn't function causing harder cold starts(???) and fan would run thinking motor is hot when it ain't).
I'm not too concerned about the fan function since I'm pretty sure there is a fuel system problem.
I pinched off both return and feed lines before with gauge hooked up, and pressure still dropped within 3 minutes. I question wether or not I had them pinched off completely, so I'm going to try and get a couple of the line/pinch plyers from a frien and try it again.

I hope it's just a bad CSI, but that wouldn't cause the obvious miss to the engine I wouldn't think.

 

Also, with motor running, car has a constant ~40lbs~ of pressure which jumps up to 45 when I pull the vaccum line off the regulator.

 

I checked the ohms on all injectors and they all checked out good(I believe). Most were ~16.5~ with 2 injectors(cly 6 & 8) being lower at ~15.5~.
The CSI was 4.5 ohms.

Two qusetions if anyone could answer;

I unplugged the CSI and I plan on just leaving it unplugged since eventually I'm going to just do away with it. Will this affect anything?

Even though the injectors ohm out ok, this doesn't mean one can't still be leaking, correct?

The reason I am set on a faulty injector is because of the miss my engine seems to have at idle. Timing has been checked and confirmed at about 6 degrees.
I notice every once in a while the engine "runs on" for a few puffs after the key is turned off.
This doesn't happen every time, but it does happen.

I may just pull the CSI from the fuel rail and mount another spare one as a dummy to block off the rail, leaving the original one in the runner as a block off.
I know thats honky, but I don't know how else to plug the fuel rail without one of the kits.

 

CSI is just a " dumb " switch ; there is no feedback to the computer
If the injector you use is known not to leak ;leaving it in as a plug works because it only operates when it gets power while cranking.
Disconnect the harness between CSI switch under TB and CSI injector so it doesn't operate. If you can't find a plug for the fuel rail then you can leave the hardline connected , no fuel will flow
Nothing honky ; just looks like stock

Yes
A injector leak is a mechanical fault ; low resistance is a elec fault

 

Thank you very much for your help vetteoz.
I do appreciate it very much

 

I finally ended up using a pair of the hose pinch-off pliers, and found that clamping the return line stopped the fuel pressure from dropping.
I guess I will have to swap out the FPR and I'm thinking it can be done without removing the plenum/runners, but can anyone confirm this?
I know it will be tight, but it seems possible.
At least I'm hoping so.

 

I am chasing a low pressure problem on my 91 TPI motor. I replaced the fuel pump but still has low pressure. I clamped off the return line - no change. I think I may have a faulty fuel pump.

You mentioned above to check fuel pressure by clamping supply line side. I'd like to know how you do this. How would I connect a pressure gauge to the fuel lines prior to the TPI rail? Thanks for your advice.

Bob t.