New Member
Well New Member Here!
Needing Some Support & Help.
My sons 1989 Corvette (just got three weeks ago not running, towed home) will not start due to the fuel injectors spraying fuel into the cylinder and loading up, at this Time.
Short history this past week. Replaced fuel pump & strainer, cleaned rust out of tank, blew out both fuel lines and replaced fuel filter that also had rust in it.
Replaced fuel pump relay, cleaned out fuel rail and installed all new fuel injectors ( 22 lbs. Bosch 3 from Fuel Connection) replaced vats lock key ignition cylinder and ignition switch,
all new spark plugs.
Go to start pressure gauge reads 40 plus then drops when key is returned to on position drops, due to injectors leaking into engine.
Does not hold pressure. Before replacement tested pump after installing went to 42 lbs. slowly went down within hours and held 10 lbs. for over 24 hours, now nothing.
The old injectors were also leaking into the cylinders but only 2, 4, 5, 6 & 8 so I figured they were dirty with rust.
At this time unplugged all injectors wires, all fuses and fuel pump relay, the wire from distributor (red) cranked over again and the same thing happens?????
Fuel sprayed out cylinders. All Spark plugs were removed in doing this test.
Removed ECM or ECC under right side dash and opened up to see a after market Chip from Hypertech (89 Corvette 350 TPI Auto, Street Runner PT. # 128981).
Not sure if this has anythig to do with it but running out of options.
I have over 80 hours in this project with no results ( good thing I love Corvettes) :D
Im going to a local car show to chill with my C5 and vent and will try to give it another go when I get back.
Need another game plan! or insight to were to go.
I have been owning, driving and playing with Corvetts for over 40 years so not just starting out, this is the first time I ran into this kind of problem or maybe just getting to old.

the first step, in isolating a problems source on these c4 corvettes is almost always to pull trouble codes, and to grab the factory shop manual, so ID be looking at those first. youll want to have a muli meter and a fuel pressure gauge and it certainly won,t hurt to have a diagnostic code reader/scanner
have you pulled trouble codes"
what is the resistance reading on the new injectors?
if the injectors still allow fuel flow without the electrical connectors attached ,to the injectors themselves, obviously theres either crud in the pindle seats that needs to be cleaned or the fuel pressure significantly exceeds the 40psi-44psi the stock TPI fuel rail system runs at.
Measured Value

Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
Engine Oil Temperature Sensor. (lower sensor above oil filter) 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.

some early c4 vettes have the gauge and oil pressure switch on an adapter near the distributor base into the block

to add something to this that is often over looked regarding MAF codes, so here it is, a direct quote from my 87 FSM which is probably the same for 85,86,88,89.

Second paragraph on both code 33 and 34...interestingly not on code 36.
Code 33 page 6E3-A-42

"The oil pressure switch or the ECM, through control of the fuel pump relay, will provide 12 volts for the MAF power relay which provides the 12 volts needed by the MAF sensor".
I personally know a few guys who cured their MAF problem simply by either replacing the FP relay or repairing the wires going into the FP relay...these wires over time may have had the insulation shrink back (mine were bare 1-2 inches, and touching) not only dangerous , but can cause all types of problems.

Oil Pressure Sender/Switch. (top sensor in picture above) 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F,

the most likely source of your problem, that matches your stated symptoms, is a ruptured or leaking fuel pressure regulator diaphragm thats allowing fuel to flow up the vacuum hose into the plenum, as its very unlikely all 8 injectors are leaking, that would account for the fuel pressure drop and all 8 cylinders showing excess fuel contamination , if its a small leak the fuel bleeds down into the vacuum line and back into the plenum, when the cars shut down, fouling the plugs, but it may just run slightly rich once it starts as the oxygen sensors partly compensate by reducing the injector pulse duration


replacement diaphragm



aftermarket fuel pressure regulator on tpi fuel rail pictures

if you have at lease 38 psi in the fuel rail, and it holds at or near at least 38 psi for at least a couple minutes after you stop cranking the engine, the fuel pressure regulator is most likely functioning correctly, but you state the injectors are not squirting fuel and the pump keeps running while you crank the engine?
you can test the electrical connectors on the injectors with a noid test light to watch the electric pulse,at each injector location, ID verify timing injector resistance,and check for vacuum leaks while testing, and remember theres a 9th cold start injector on the 1985-88 TPI fuel rail


as always a simple, step bye step approach where you verify the function or failure of each related component in the system before assuming any components working correctly is the smart route to take. never assume you know some component functions or is at fault until its tested carefully, and remember to verify proper voltage, resistance OHMS and ELECTRICAL GROUNDS


MAF Problems

Faulty MAF sensors will normally light the check engine light on the drivers information center if the problem is constant and store a trouble code. If intermittent, a trouble code will still be stored as long as the battery is not disconnected.

Normally, the problem is a poor connection at the sensor and wiggling the wires, unplugging and reinserting the connector will often cure the problem.

A faulty MAF will normally cause a no start or difficult start condition and although you can eventually get the car into the "limp-home" mode in most cases, you need to attend to the problem ASAP.

AC/Delco sensors can become intermittent or give false readings if the wires become contaminated as explained above.

The MAF is a critical part of the emission control system and as such will cause the computer to react to problems very quickly, setting trouble codes and reducing performance in ways that cannot be ignored for long.

MAF Mods

The Bosch MAF is often modified by removing the two screens that are present in the front and rear of the cylinder. Removing these screens significantly increases the air flow through them and this results in more horsepower. Removing the screens is an old trick from the Corvette Challenge days in 1988 and 1989. It does work but is illegal in many states so be advised not to do anything that will get you arrested for a pollution violation.

The AC/Delco MAF is not readily modified. It is what it is but since it is a larger diameter than the Bosch, it responds well to changing the air filter to a free flowing type such as the K&N filter."



http://www.mamotorworks.com/corvette-c4 ... 6-893.html
http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf
now keep in mind the, fuel pump supplies fuel flow, the fuel pressure regulator restricts fuel from leaving the fuel rails untill pressure exceeds about 42 psi, each injector is basically just an electric solenoid that controls an internal valve in the injector thats NORMALLY in a closed position, until, the electrical pulse OPENS the injector, if you removed the electrical connectors the solenoid should remain firmly shut.
(Id remove the aftermarket chip during testing as Ive seen a very high percentage of those aftermarket performance chips cause problems after a few weeks of run time as they seem overly prone to defects)



the injector is supposed to be effectively a sealed valve controlling flow of fuel until voltage is applied forcing the solenoid to open the injectors internal fuel passage, and no fuel should be able to drain thru the orifice,if it does, even though the injectors may be new ID be strongly suspecting that debris in the tank or lines has entered the injectors ,water carrying micro crud or rust into the fuel line, and into the injector is preventing its full closure, as thats the only logical way fuel can pass thru a disconnected injector receiving no electrical current.
it only takes a very small amount of rust/dust/crud in the fuel flowing thru an injector to let it leak or jam the pindle seat partly open, so don,t assume NEW injectors can swallow that sludge with impunity.
the factory fuel filters are BARELY adequate for clean fuel

the next step is to use a multi meter and verify injector resistance, it should be consistent within an OHM or two between all injectors depending on brand most c4 corvette injectors will read 12-15 OHMS resistance.
Id then check the fuses and use a NOID test kit



to verify the injector gets an electrical pulse at the electrical connector, remember each bank is separately fused on some year c4 corvettes
Dirty or partially clogged injectors can show up in many ways and may include:

- "Check Engine" light or cylinder misfire code
- Poor idle
- Light throttle surging or bucking
- Denotation (knocking or pinging), causing possible engine damage
- Low speed hesitation and surging issues
- Emission problems
- Loss of performance
- Increased fuel consumption

Leaky injectors can cause:

- Hard starting, especially when hot
- Poor idle
- Emission problems
- Increased fuel consumption
- Exhaust odor


Theres a great deal of related info, in these links
















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The stock fuel pressure for 1985 to 1987 C4 engines with TPI was 36 to 39 psi with the fuel pressure regulator vacuum hose connected, and 47 to 48 psi with the vacuum hose disconnected. For the 1988 to 1996 C4 corvettes, the stock fuel pressure is 40 to 42 psi with vacuum hose connected and 47 to 48 psi with the vacuum hose disconnected.

swapping out the stock non-adjustable fuel pressure regulator requires removing the plenum but takes only about 20 minutes and its easy to do, it allows some minor tuning adjustments which tends to help power.ESPECIALLY if the stock FPR is leaking.
also be aware that a leaking injector, or fuel pressure regulator can cause the catalytic converter, to melt internally, blocking the exhaust flow or oxygen sensors to fail



http://www.chevythunder.com/fuel%20inje ... pg%20B.htm


be VERY SURE you order a adjustable fuel pressure regulator that comes with a NEW matching diaphragm as many kits assume youll re-use the stock diaphragm


if you swap to an adjustable fuel pressure regulator on your TPI fuel rails it makes sense to install a small fuel pressure gauge on the fuel rail so you can easily verify your fuel pressure, keep in mind raising the fuel pressure tends to richen the effective fuel/air ratio slightly while reducing the pressure tends to lean it out
slightly, but remember the computer and the oxygen sensors try to maintain the emission friendly 14.7:1 fuel air ratio

http://www.jegs.com/i/JET-Performance/5 ... ProductId=
I have not had a chance to get back to this project just yet, I have to take care of some other business at this time, but will keep you posted as soon as I can.
Will go over the basics again starting with the fuel pump and work my way to the start up problem.
I do have all the equipment you mentioned and been doing the same tests, before I asked for some help.
There is no way to check codes if this engine has neve ran. It only started and then died before I tryed to get it running, the cluster was not working at that time but fixed or found the problem and corrected it.
I will start again with the basics and see where it leads me.
I still am leaning towards electrical problem.
You mention removing the chip but I do not have the stock one to re-install seeing we just got this car.
Thanks for your time and information.
Excellent information for finding and testing the system.
But still not finding the problem.
I have not had any time except to recheck the fuel pump, which did not pass.
Blocked off the return line at the tank and powered up, went to 60 + lbs. and dropped down.
This way I by pass the fuel lines and pressure regulator so just testing the pump.
New pump also. When it was first installed I tested it and it worked as designed. Powered up and held pressure .
I suppose I will be returning it and getting another one before continuing when I get some free time.
If that works I will be removing the fuel rail and testing it off the car fully assembled as if it was in the car to see how many injector are leaking.
Will keep you posted as soon as I can.
Carlisle is coming up so I have to play with my (2000) C5, clutch pedal sticking to the floor, before I take off.
"Blocked off the return line at the tank and powered up, went to 60 + lbs. and dropped down.
This way I by pass the fuel lines and pressure regulator so just testing the pump."

while thats true, if your getting 60 psi with the fuel return line block, then the pressure drops off its very unlikely to be the pump, its far more likely to be a leaking injector(S)....blocking off the return line eliminates the fuel pressure regulator from being in the circuit, but getting 60 psi makes me suspect the pumps good, Id be looking at the injectors




http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

http://fuelinjectorconnection.com/shop/ ... groupid=72


http://members.shaw.ca/corvette86/Engin ... ontRun.pdf

http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf



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heres some newer holley efi/ignition connection info and links to EFI systems
theres no question EFI has advantages it only the initial cost, and in some cases the steep learning curve that makes it seem like an option thats best avoided in older muscle car applications, but the ability to self adjust and in some cases self diagnose problems, better fuel ratio control, easier starts, makes it a good idea

http://www.holley.com/data/TechService/ ... 5rev11.pdf

http://www.holley.com/data/products/pic ... 50-836.jpg