My car has had starting problems that have been progressively getting worse. Aprox 3k ago the car would take about 5-7seconds worth of cranking to fire up. This was following by even more cranking time followed by a very weak startup. I would typically need to gas the throttle a big to get the idle to even out. Now the car will almost refuse to start. If i let it crank for 7-10 seconds and then stop and try again I will instantly get a weak start that I can try to throttle to life.


This only seems to occur on cold start. Warm or hot starts are strong and fast.

Car drives fine when started. There may be a slight miss at idle but that may also just be my inexperience with an older SBC

Items replaced;
ICM
Dis cap& rotor
Plugs
Wires
The I/M was taken off and resealed
Fuel filter changed

On stock injectors
Timing set correctly.

This is a 4l65e TPI

Thanks

 

I'll be watching this thread as I'm having just about the same symptoms with my '89. It used to start first piston up, but after a blown head gasket with a subsequent top end overhaul, it now takes 4-5 seconds of cranking to start, then a really rough idle for about the same time before smoothing out.

Hot, it starts fine but still with a couple or three seconds of cranking then a smooth idle.

I have new injectors recently installed which made no difference. There's no air leaks in the plenum or runner gaskets verified by spraying carb cleaner around to no effect. My fuel pressure is right on the money.

Plugs? I dunno. They hardly have any miles on them since the head work - though I'm not sure the mechanic changed them. It's been a couple of years ago, memory fades and I really don't trust what he might have said (or billed me for). He was kind of a hack. He didn't even put all the bolts back in and forgot to hook up vacuum lines, etc. I fixed several items when putting in the new injectors.

 

I did try cleaning the Maf just now with some electrical contact cleaner, seems like it hasn't helped. Although this time I did only let it crank for 2-3 seconds, stopped, tried again, then it fired almost immediately and had another weak start but leveled out on it's own to a 1K RPM idle for a while.

plugs were changed, pretty sure they're platinum's or regular coppers, nothing out of the ordinary. Gapped correctly.

Maybe the FP relay? I'm really just reaching here given it starts fine hot, and whenever I let it crank for a while and then stop, to try again.

 

Have you removed the battery terminals and cleaned the posts? I had problems with cold start caused by corrosion I couldn't see without removing the terminals. I cleaned them and the posts with vinegar and sprayed both with red anti-corrosive I got at Walmart and it starts fine now. Battery voltage looked fine prior to cleaning 14.2v.

 

Battery looks relatively new and the posts are completely corrosion free.

it has no problem cranking, it just doesn't want to actually start firing.

 

What year? '85-'88.Cold start injector or circuit?

 

89 with Bosch MAF. I'm not familiar with what you referring to?

 

Cold start injector was discontinued in '89. That won't be the issue. Have you checked the fuel pressure after a cold soak? Should build up quick, sometimes won't even get to zero. Regardless of the residual pressure it should jump up quick on key up

 

I don't have a fuel pressure gauge reader, I've been trying to diagnose everything else before dropping a c-note for a master kit from harbor freight (as it's the only one that can read GM)

 

Sounds like the fuel pump is not running when you turn on the ignition. It should run for 2 seconds to prime the fuel rails for starting.

The technical stuff: The ECM turns on the fuel pump through the fuel pump relay for 2 seconds when you turn on the ignition. It then shuts off the fuel pump, so it won't run continuously if you turn on the ignition but don't start the car. When the ECM sees DRPs (Distributor Reference Pulses) from the ignition module during cranking or running it turns on the fuel pump again and it runs as long as the ECM sees DRPs.

If the fuel pump relay circuit fails there is a backup system. There is an oil pressure switch that turns on the fuel pump when the oil pressure reaches 4 PSI (that's hearsay -- I've never seen that number in a publication from GM). The switch bypasses the fuel pump relay and applies 12 volts directly to the fuel pump.

It sounds like you are running on the oil pressure switch, which is why it takes so long to get the engine running. Check that the fuel pump is running for 2 second at ignition on. I can only hear mine run if the AC and radio are off.

The fuel pump relay is next to the windshield wiper motor. The oil pressure switch is on the back of the engine next to the distributor on the driver's side.

 

Good stuff! Thanks! I'll check this out today!

 

I just bought (and have used successfully) this $20 kit from HFT. Fits the 1989 Vette jus' fine.



http://www.harborfreight.com/fuel-in...ter-92699.html

All I used out of the kit was the gauge and the hose at the bottom. Be sure to use Teflon tape for the gauge connection, per the instructions.

 

oh man thanks a million! I looked at that kit first but when it said 'not compatible with GM TB systems' I thought I'd have to upgrade to the master kit.

I'll pick it up today!

I'm going to replace the relay, it's $13 from autozone. I think I heard the pump cycle while I had my helper cycle the ignition only once out of 10 tries.

 

Anything without a Cold Start (and it's still true for those years too once it's running), the amount of fuel it gets is determined by the Coolant Temp Sensor Signal. Acting in place of a Choke, the length of time the injectors are held open is proportional to temperature - colder more/hot less. You start with a Scan to see what it's sensing cold and that should match ambient and the air intake sensor and if there's a wide variation, plug a new one into the harness (you don't have to install it yet) and see if there's any difference.

Relays are rarely if ever intermittant - they either work or they don't, so I'd spend 9 Bucks on the Sensor if you thought you heard it work.

Get a scanner or something to see Sensor input too so you and all the rest of us don't have to guess and please post your Year when you have a problem.

For the guy with the rebuild following a blown head gasket; check valve adjustment; particularly if it's not running right after it starts.

 

That was me. The head work was a couple of years ago. It had nothing to do with my current (new) problem. I think this one may be an intermittent connection fault on the IAC plug. One time it runs fine, the next time the idle will drop out, then it's okay again. Worked fine today.

 

just from a quick look, it appears my car has a manifold air temperature sensor(no airbox IAT), access to this is... difficult.

How do you suggest I 'scan' this. Measuring resistance with a multimeter? What range should they be in?

 

A Scanner plugs into the Diagnostic Port and converts Serial Data into meaningful information; ie, you'll see what the ECM is seeing to run the engine. For '96 and up, you can pretty much use a Cellphone/IPad with the right App and Cable (Delphi just introduced their own which was reviewed in Poplar Mechanics). Haven't seen many useful Apps for older systems, but you might do an Android or Apple Search. Assuming you can't use your Cell, you'll need a dedicated device. There are also Cables for a Laptop and software available over in the Scan & Tune Section (or if you post there, someone will give you the info).

 

Replaced coolant temp sensor, had a little bit of a drama with a crushed distributor wire causing the car to refuse to start, so I'll have to wait until the morning to see if it made a difference.

Which Scanner would you recommend? My knowledge of obd1 extends to knowing that its very manufacturer specific and finicky..