fighting a 95 blazer with cpi

[sterlclan]

I installed a rebuilt long block into my 95 s10 blazer. i drove it in the shop to swap engines and now cant get it running. it started right off but ran stupid rich.it had a rv style cam in it then,i pulled the intake to fix a sticky lifter and put a stock cam in.cam timing is on,ive checked it multiple times. it has 50 to 55 psi fuel pressure static no change while cranking,new reman cpi all sensors appear to function as expected using the scan tool.when you try to start it it gives a little squirt when priming the injector but spews a ton of fuel when cranking.it will flood before it starts. unplugging the o2 sensor has no effect scan tool still says lean.compression is equal within 5psi across the board. im stumped if i unplug the map sensor no change. the only code is for esc sensor or module but that was present in the old engine. the coolant temp sensor reads actual temp,map sensor shows a drop in pressure when cranking ignition timing as close to tdc as i can get it without it running.any idea where to start?

[dave w]

Maybe the fuel pressure is incorrect? Maybe the return fuel line is kinked and causing to much fuel pressure?

dave w

[sterlclan]

i blew through the return line with air ,seems like it flows fine got air out of the fill cap. i am changing the filter today and trying again.the pump is only a year or so old.

[1project2many]

Reman spider could be an issue. Scantool definitely showing correct values? Wrong rpm at crank, wrong CTS, wrong MAP/MAF, wrong TPS? Any of those can cause excess fuel. If sensor readings are good confirm control (-) wire to injector isn't pinched or shorted to ground then inspect / swap spider. There isn't much else that could cause the problem and the spider is untested/unknown.

[sterlclan]

same issue with the original spider,swapped it for a reman to eliminate that cause,today verified all grounds to ecm changed filter rechecked ign timing still flooding. the tool seems to be right the throttle movement shows up the coolant sensor changes with ambient temp as does the intake air temp sensor map sensor value drops when cranking and shows proper baro pressure when not ambient temp shows up im guessing the rpms are about right hard to tell when just cranking it changes though.

[Fast355]

Wrong memcal perhaps?

[sterlclan]

same memcal that ran it when i drove it in the shop. the control wire for the injector is showing a ground when the ecm is plugged in but not when its unplugged. the continuity tester shows a steady ground while cranking is the tester too slow to detect pulses? the ecm shows a number for pulse width so i assume it thinks its working right.same symptoms with a reman ecm that i had in stock.

[dave w]

If I were facing the same kind of problem, I might do some dangerous and out of the box troubleshooting. Sometimes bad things happen when troubleshooting a fuel problem, so keep it safe and have a fire extinguisher ready.

I might depress the gas pedal to the floor to put the computer into "clear flood mode" when cranking the engine, keeping the CPI injector from spraying fuel. Eventually, the engine should start and run for a few moments. It's possible clear flood mode doesn't work so I might unplug the CPI injector or unplug the fuel pump relay and see if the engine stops flooding.

Maybe fuel is constantly by-passing the CPI injector and the flooding the engine?

dave w

[sterlclan]

it will sputter and almost run with the cpi plug undone, it will catch some than there is no fuel left.ive removed the top of the plenum and left the spider laying there no fuel out of the poppetts till you plug the injector in and crank it over then too much.should the signal line be grounded all the time the ecm is plugged in without running?im going to get a noid light today and wire it to the injector that should show a pulse in the signal when cranking right?it almost seems like it gets a solid ground instead using my continuity tester. being the injector is a valve if it stays grounded it would stay open correct?

[sterlclan]

Noir light shows a pulse while cranking it almost started where it was twenty degrees in the shop but didn’t stay running for mort than a few seconds now it’s flooded.

[sterlclan]

going to look at a replacement ride for her, ill fix this stupid thing i just ran outta time she needs dependable transportation and i fear this pos may never be that. if it had a carb id be driving it now,this is why people hate injection,its very frustrating to drive something in and now can not.only thing i can figure is i damaged the harness in some way and to gain access to that the engine will need to be pulled.with snow coming and other work i have no time thanks to all and i will keep you informed.

[dave w]

The computer pulses GROUND to the injector connector to cycle the CPI injector on / off. One wire on the injector connector get power from the ignition switch when is ON or CRANKING, the other wire to the injector connector gets GROUND pluses from the computer.

Several years ago I helped a co-worker with a similar problem, which ended up being a kinked return fuel line at the gas tank causing fuel pressure much higher than factory specification. Makes me wonder what your fuel pressure is?

dave w

[sterlclan]

the pressure is 50 to 55 psi static or cranking,i can blow air in the return and hear it in the tank, the lines do run along the top of transsmission and the trans did drop some while pulling the original engine i just spoke with ed by phone and have some more things to check ill try bypassing the return line and go from there i will fix this thing eventually ill will keep you all informed.

[sterlclan]

Checked fuel lines no blockage. Replaced prom with correct one and tried both ecm still flooding it will run with the booster vac line open and half throttle or more poorly huge black cloud. Static fuel pressure is fifty five holds fifty with key off for fifteen min. Or better drops to fifty two or so while cranking is the pressure too low? Still don’t get the rich condition it just dumps the fuel in pulses but looks like a holly double pump accelerator squirt every time.

[dave w]

Maybe replace the spider assembly? https://www.rockauto.com/info/321/217-3395_Primary__ra_p.jpg

Maybe replace the computer? https://www.rockauto.com/info/1/776395-fro__ra_p.jpg

dave w

[sterlclan]

Maybe replace the spider assembly? https://www.rockauto.com/info/321/217-3395_Primary__ra_p.jpg

Maybe replace the computer? https://www.rockauto.com/info/1/776395-fro__ra_p.jpg

dave w
already done. rebuilt ecm no change,reman injector swap between any of them same symptoms. new nos prom as well any combination of parts same thing what am i missing? grounds check good all the sensors appear to function as expected. even swapped some of those from the parts rig no change. how can i shorten the pulse width on the injector? seems to me that a quicker pulse would lessen the fuel its puking. and the main stumper why did it run to drive it in and just like that wont????

[dave w]

The injector flow setting will change the injector pulse width.

For example an injector flow of 50 lbs / hr: we will say for argument sake is 8 milliseconds at 4000 RPM with an engine load of 75 Kpa.

For example an injector flow of 100 lbs / hr: we will say for argument sake is 4 milliseconds at 4000 RPM with an engine load of 75 Kpa.

Increasing the injector flow rate "makes the computer think" more fuel is flowing, so it reduces the time the injector will spray fuel.

With the computer wire harness unplugged from the computer, and the injector connector unplugged from the injector along with the pulling the injector fuse, I wonder what the resistance is between ground and the two wires going to the injector are?????

I also wonder what the resistance of the injector measures, measuring the two electrical prongs on the injector?

dave w

[sterlclan]

The injector flow setting will change the injector pulse width.

For example an injector flow of 50 lbs / hr: we will say for argument sake is 8 milliseconds at 4000 RPM with an engine load of 75 Kpa.

For example an injector flow of 100 lbs / hr: we will say for argument sake is 4 milliseconds at 4000 RPM with an engine load of 75 Kpa.

Increasing the injector flow rate "makes the computer think" more fuel is flowing, so it reduces the time the injector will spray fuel.

With the computer wire harness unplugged from the computer, and the injector connector unplugged from the injector along with the pulling the injector fuse, I wonder what the resistance is between ground and the two wires going to the injector are?????

I also wonder what the resistance of the injector measures, measuring the two electrical prongs on the injector?

dave w
injector is no resistance both wires to ground open.

[dave w]

The generally accepted CPI injector resistance is between 1.30 - 1.70 ohms. A good quality / calibrated Ohm meter is needed to accurately read injector resistances. Odds are; a new in the box CPI injector will also read no resistance with a low quality / un-calibrated ohm meter?

dave w

[sterlclan]

I will check again with a different meter when I bring it back in pushed the frustration outside for a while