Engine runs, terrible stumbling / hesitation

[CarlosJavier]

I got my hands on a 1980 Spider that hadn't run for a long time. I put in a new battery, starter, spark plugs, fuel pump, fuel filter, and replaced some rotted fuel hoses to see if it would run. I emptied out the gas tank, gave it a so-so cleaning, and put some new fuel in and the car started up and went through all gears, albeit on jackstands and with an engine miss. I put some load on it for a by applying the brakes and the thermostatic fan even came on. I traced the engine miss to two injectors - one was barely spraying and another was stuck open. The car would start both warm and cold. After seeing that the car still has life in it I ordered a set of reconditioned injectors and for the next three weeks I concentrated on thoroughly cleaning out the gas tank, fuel lines, and fuel rail in preparation for their installation.

I installed the reconditioned injectors today and and now the car does not want to start, no matter how much or how little I press the gas pedal. It will occasionally sputter, as if wanting to start, but that's the most it will do. All spark plugs were firing three weeks ago, so I doubt the culprit is in the ignition system. The fuel pump is developing pressure; a bunch of fuel sprays out when I crack open the cold start injector hose clamp. I fiddled a bit with the idle speed adjustment screw and a/f mixture adjustment screw, but neither resulted in any improvement.

Interestingly, I disconnected the ignition coil and cranked the motor a few times. There was fuel pressure in the lines, but the spark plugs did not smell like gas when I removed them...

So, facing an imminent sunset, I decided to put down my tools for the day. That's where the project is at folks, any suggestions will be greatly appreciated. Thanks in advance!

*UPDATE* - Engine runs now but hesitates badly, especially under load.

[narfire]

By chance you did'nt disconect the injector grounds while changing and not re-conect(two leads on the intake plenum) when putting back together? If you pulled the whole rail off, to swap injectors, one would generally disconect the grounds.

[CarlosJavier]

I remember disconnecting and putting back a ground wire on the plenum bolt closest to the brake booster... Where on the plenum is the other ground wire supposed to be? Thanks.

[narfire]

On/in the wiring harness that contains the wires for the injectors and all the sensors,there were/should be two short wires with circle conectors that the 10 mm intake plenum bolts slide through. There are two on my 80 and two on the other one I bought recently. Did you get the sensor in that @#$%& place under the intake on OK as well as the one on the "T". I found the one on the T,if it is on the high side it can contact the hood liner and dislodge easily. Perhaps if you have access to a "noids light" to check if the injectors are getting a current might help. I use the "Geo" size from Snap-on.
Something weird though,as I think the FI is a great system and Thought fairly easy to sort out.
Good luck

[CarlosJavier]

Quick update: I had a bit of spare time this morning, so I cleaned the two injector grounds on the plenum, but the condition did not improve. All the engine bay FI harness plugs are connected and the fuel pump comes on when the AFM moves. Hopefully I find some time within the next couple of days to figure this out. Thanks for the suggestions, keep them coming!

[CarlosJavier]

New update…

Removed the rail and injectors from the manifold but left all the hoses and plugs connected and cranked the car -> the injectors did not spray fuel.

Put a circuit tester on the harness’s injector connectors and cranked the car -> The tester’s light would come on and off; there is a pulse at the connectors.

Put the ignition in the “ON” position and measured the voltage at the harness’s injector connectors -> 12 V at both terminals of each connector.

Attempted to measure the voltage at the harness’s injector connectors while cranking the motor -> No result, the car’s battery died. Will try again later with a fully charged battery.

Momentarily wired the injectors directly to a battery -> the injectors sprayed fuel.

The harness is sending injector pulses and the injectors work when hot wired to a battery, but not when connected to the harness.

So it seems that either:
1. The ground being pulsed to the injectors is not strong enough to trigger them, or
2. The continuous voltage supply is off. What should be the continuous voltage to the injectors? Should it be measured while cranking the starter or with the ignition in “ON”? Should the voltage be the same at both terminals of the connector?

My next steps will be to hunt down and clean the FI grounds, and to research the voltages I should be getting at the injector connectors. Any tips will be greatly appreciated…

[So Cal Mark]

I've run across this on a couple of cars lately. If the battery is not fully charged, apparently there are enough voltage drops in the system that will prevent the injectors from pulsing.

[rlux4]

Good call Mark. I hadn't heard of this symptom anywhere, manuals, forums, or diagnostic troubleshooting guides. I've been trying for a while to diagnose an intermittent idling problem. Sometimes at stops the car would drop the idle down to a couple hundred RPM, sometimes even dying. I had just zeroed in on a low battery as the culprit. I didn't notice it until I tried to start the car with the headlights on and there wasn't enough current to get more than a click. Being a low battery makes sense, because keeping the revs up to 1000 or higher and the car runs smooth as silk.
I had planned on reporting this symptom on the forum, so it's good to hear from you that I was not out in left field.
Ron

[majicwrench]

Once a car is running battery is of little concern, electrical system is running off alternator at that point. Odd of a weak battery causing a dying at idle very slim.

As far as injectors, I would bet the issue is going to be on the ground side of things. Way to find out.......ground the neg side of injector, now crank over the car, it should spray continuosly . If it does, plenty of current getting to injector. If it does not spray, now hook voltage up to hot side of injector, and remove the ground from step one. Crank again, now should pulse spray.
Course if yoiu have a lab scope this would take seconds and you would not have to spray fuel all over.
PS Disable ignition during all this!!

[rlux4]

The odds may be slim, but that's what it was magicwrench. The battery I had in my car was a cheapie that the PO put in three years ago to get the car running for sale. My thoughts are that the alternator is charging the battery as the car runs, leaving little left over for the rest of the electricals. Particularly considering that the alternator in these cars is barely adequate. Acutally I was relieved to hear that Mark had run into the same symptom, I had the same thoughts as you at first, but nothing else was the cause, and a new battery fixed it.
I'm going to reasearch it, but I'm thinking that the heavy brown wire from the battery straight to the dual relay may not get enough amperage with a weak battery.
Ron

[So Cal Mark]

I've had 3 FI cars in the past 2 months with this symptom. They all were cars that had been sitting mostly, driven infrequently so the batteries were low. The car cranked, almost normally, just a tad slower than normal. On each of these cars, the injectors would not pulse even though they had run normally the last time they were started. On each of them, the entire FI system passed all tests. Once I disconnected the #1 injector connector, grounded the return circuit to force all injectors on, the cars started and ran. Once the batteries were brought to full charge, no problems

[majicwrench]

To clarify,
I can certainly see how a weak battery can cause the injectors not to fire on START-UP.
Weak battery is not, however, going to cause dying at idle.
Keith

[carl55]

The weak battery is pulling all the juice.

[spider2081]

I would think its a good idea to jump the car with with either and a battery charger with a start position (80A or better) or from another car that is running and capable of charging the battery of the car that is not starting. The car being used to jump the other car should be running about 1500 rpm to be sure it's alternator is carrying the load of the weak battery. The voltage output of a weak battery can easily drop below 11 volts when cranking the starter. this could be too little for the injectors to pulse or too little to make a good spark needed to start a less than perfect engine. Most cars alternators put out 14 plus volts when charging. Percentage wise that is a big change from 11v of a weak battery.

[So Cal Mark]

the deceptive part of these cars is that they didn't sound like they had low batteries. Cranking speed was just a touch slower than normal, but it's not like they were barely turning over. I recently ran across a guy with an Alfa using the L-jet system that had the same problem. A contributing factor could be that since these cars had been sitting, the injectors were a bit sticky. Forcing them to cycle by providing direct ground may have freed them up