Hi, i am new to posting forums but have been reading them for years. i have a real problem with starting up my car and i have tried most everything i can think of plus asked a hundred different mechanics. I have a 1988 with LT1 with TPI think it has been bored out to a 383. there are a ton of mods on the car some of which i dont have records for as i am probably the cars 4 owner. recently ran great but now She turns over and over with occasional sputter but won't start. Spark test is positive/ has spark. Replaced fuel pump and filter. Has pressure in at the rails. Thought it was a vats problem but a byPass didn't fix it. Thought it was the ECM replaced that and still just rolls won't fire up. Sprayed starter fluid into mass airflow sensor and it fired right up and ran till it burned up the starter fluid so i am positive that this has to be a fuel supply problem.

I'm seriously confused and have spent $$$$$ trying to get past this what else could it be? Injectors? Wiring harness? I still can't tell if this is an electrical or mechanical problem. or how to go about a fix.

Any advise is golden at this point because i have only basic mechanical knowledge and this is my first Corvette.

 

OK, you mentioned it has fuel pressure.....how many lbs of fuel pressure at the rail?

During cranking, are the injectors pulsing (test with a noid light).

If it starts with starting fluid, it's a fuel delivery issue. If you've got around 40 psi and it holds pressure, you've got an injector issue.....probably ECM related.

Post your results of these tests and we'll go from there.

 

thanks for the reply!!

yes i have tested the injectors with a light and they are not receiving any signal, no pulse. this lead me to believe it was a ECM related problem.. so i went out and got a new one yesterday and plugged it in...no change and still no start. I don't have a fuel pressure gauge however whenever i depress the nipple fuel sprays out. i assume the proper tool is a better tester than my method.(I will get one)

this car previously had an intermittent start problem where this same situation would occur from time to time, sometimes stranding me places. it would right itself with no intervention after leaving it overnight sometimes and this baffled me. when it would start it ran strong with no problems or sputters but after driving for a while and shutting it off it would refuse to start again..

now it just lies dormant and has for months. these signs all lead me to believe Electrical was at fault. and now i own two perfectly functional ECMs as the brand new one has failed to solve the problem. (re-manufactured ECM's don't need to be programed prior to instillation to function do they?)

Are there any specific wires/connectors i should look more closely at for faults, is there a fuse for the injector system, would this come up on a Dino ERROR code if i got it looked at in a shop?

i am just skeptical about tearing apart my injectors as the signs and symptoms lead me to believe it is more electrical than mechanical+I just replace the starter fuel pump and filter thinking they could have been the culprits.

 

If you used a noid light and the injectors aren't firing then first check the fuses. There should be a 10A fuse for each injector bank, then they fire off on receiving the ground pulse from the ECM. Did you swap in an LT1 ECM or are you using the L98 ECM?

 

What sort of a VATS bypass did you use? If you just used a resistor to bypass the pellet in the key--the VATS module (which "reads" the key pellet) may be the problem-the VATS module in turn sends a signal to the ECM which then "enables" injector pulse.

There are kits on the market which completely eliminate the VATS and send the correct signal to the ECM--OR "tuners" are able to remove VATS via programming. You would have to check whether or not that is possible for the ECM you are running. There are vendors here on the forum which should be able to tell you if it can be done on a '88 ECM.

 

One thing you could try is to unplug all of the injectors and check for injector pulse. If pulse is now good it's a good sign of a shorted injector. My kids car was doing something similar. And after a couple hours of diagnosing thats what I found. Bad injector plugged in no pulse on any , unplug bad injector got pulse on all. Did you check for pulse on more than one ?

 

The question is do you have an '88 L98 or a '92+ LT1?

 

 

If you have an 88 the module in the distributor is probably bad.

 

Measure fuel pressure, it should be 35-42 psi and it should hold up for at least 1/2 hr after the ign is off and if it doesn't, you have leaky injector/s or a defective check valve in the fuel pressure regulator. You cannot use any old light to check for injector pulses during cranking, you should use a noid light available at parts stores. Check both INJ1 and INJ2 fuses with an ohmeter, ohmeters , "see", better than you do! Let us know what you find with these tests because there are other tests depending on results.

 

The fact that the problem progressed to this point, leads me to believe that a short in an injector may be knocking out the ECM's injector driver, or the ignition module that sends reference signal to ECM, is failing. I wouldn't rule out a poor connection at the 4 pin connector to dizzy, either.
As mentioned, unplug all the injectors and then look for a pulse in your noid light.
Use an ohmmeter and check the resistance of each injector coil, looking for 15-17 ohms.
Also as mentioned above, what bypass method was used ?
Are there any stored codes ?
Service manual says the reference signal from module to ECM is 1.3v. Terminal B5(24 pin connector) at ECM is the input. Maybe you can see if that terminal is getting that 1.3v, during cranking.

 

im working on going through all the tests as described still waiting on getting a couple tools like fuel pressure gauge, and full set of noid lights which ill have later today.

The vats bypass i used was one that plugs in to the ignition wires below the steering column and just matches the keys resistance #.

as for the engine it is a LT1 boared out to a 383 i think. It had a AC delco re-manufactured ECM in it(had removable chip on circuit board). the replacement one i picked up at Kraigen, and seemed to be a generic RE-man for any 88 corvette. I don't know if my engine requires a special ECM or not but when i plugged it in nothing changed so i kept the old one because it is most-likely still good.

as for codes I am not sure however the check engine light has come on and off in the past indicating some may exist.(don't own a code reader but will borrow one).

 

No special tool required to get the codes, it's just a matter of jumping "A" and "B" on the ALDL connector, turn ignition to run and count the flashing SES light.

Read these for more info.

http://www.corvettephotographs.com/c4vettes/codes.htm

http://members.shaw.ca/corvette86/No...it%20Check.pdf




Do you have a DMM to test each injector ?

 

so i got through some tests today. some hints nothing conclusive. didn't get to test fuel pressure yet or injectors with noid light soon though. did test the injectors with multi tester an got and equal resistance on all 8.

checked for codes after I was instructed on how to read them (thanks agent 86, and the links you posted were immensely helpful) received code 46.

i also checked my inj fuses with test light and they were fine. one is 5 and other is 7.5.

another interesting thing, when i tried to start it today it fired immediately and ran about one engine cycle or 2 seconds then died out and continued the normal behavior. at least some gas or even fumes must be getting down through the injectors. I know i still need a conclusive pressure test.

 

code 46 is the VATS Fault code.

so i already measured resistance of my Key at the dealership and bought a matching resistance key bypass for that and installed it.. that didn't do it and was done months ago.

I discovered a rats-nest of wires under the passenger Kick panel all leading to a security system box that appears to be inactive.( security light flashes from time to time but the horn is disconnected and has been since i have owned it, probably cuz the alarm was always going off. I know they wanted these cars to be hard to steal but this is crazy.

So now i must look into other VATS bypass options. weather its a faulty key/ignition switch, other security issues i am unaware of, or can VATS be repaired? a bypass altogether as long as its fairly simple would be great.

feels like im getting close and i cant wait to drive her again.

 

I was afraid that was going to be the code.

Is this rats nest around an aftermarket security system, or the factory one ?

Read this and do the ECM enable signal test, page 8A 133-12

http://members.shaw.ca/dankai/Vats%20Electrical.pdf

 

does this test require taking out most of the dash (passenger side) to find the VATS Module? It is still not clear to me where exactly this part is. the testing instructions and diagram are helpful though.

if i do find that the module is bad i obviously have to replace it, however if it is still good then what?

the rats nest of wires is more organized than i made it out to be and connect an aftermarket(no indications that it was a GM part) security system via plug in connectors.

I am interested in the fix that involves reprogramming the ECM. This sounds like less of a haste and eliminates the problem of a repeated VATS failure.
Do you know if this is an option that would work for my car/ECM??? Or does this only work with a "programmable" ECM.

i have been looking and it seems like this happens to tons of people. unfortunately all the forums end right before they say they what fixed the problem(pertaining to this crank no start code 46).

 

I just remembered something else as well.... my car is a Manuel 4+3 but the clutch switch must have been disabled because I have always been able to start the car without depressing the clutch. could this have any thing to do with it?

 

Clutch switch wouldn't cause a VATS code 46. The VATS decoder module is in the same area as the ECM--you shoudn't need to remove the dash. I'd continue the test that Agent86 posted and be sure you don't have a wiring or connector issue between VATS module and the ECM.

If the VATS module turns out to be bad--you could replace the module which would also involve replacing the "bypass" you've already installed with another "resistor" to match the new module OR use the search feature here on this forum there are previous threads which describe bypass modules which send the correct signal to the ECM for injector enable OR as I said before contact one of the vendors here and see if programming VATS out of the ECM is a option for your ECM w/MEM/CAL chip. It can be done on the later ECMs--IMO it's doubtful on yours, but it would only take a phone call to be sure.

 

www.vatssucks.com

www.bakerelectronix.com/products vats

the "complete" bypass is listed under products in the second link