FAQ
TL;DR: In this thread, 1/1 confirmed fixes = "It's a computer" (failed ECU) after choking on throttle and MIL on. [Elektroda, miki1203, post #16853742]
Why it matters: This FAQ shows how to quickly triage Seicento 1.1/0.9 stalling with the injection light, even without a scan tool; it’s for DIY owners and techs who want fast, forum-proven checks.
Quick Facts
- Symptom pattern: stalls when adding gas, injection light on; reversing shows no issue. [Elektroda, miki1203, post #16827048]
- The ECU stores faults even after power disconnect; read codes first. [Elektroda, sandamiano, post #16827312]
- Vacuum leaks at the brake servo line can upset mixture and cause stalling. [Elektroda, andrzej20001, post #16827512]
- Engine movement in reverse can tug hoses/grounds, changing symptoms directionally. [Elektroda, tzok, post #16827895]
- Final outcome here: failed ECU reported by the OP. [Elektroda, miki1203, post #16853742]
What does it mean if my Seicento chokes on acceleration and the injection light turns on?
That pattern points to the engine going lean or losing critical sensor input during throttle. The MIL turning on means the ECU detected a fault and stored a code. Reversing normally can mask movement-related issues. Start with fault-code reading to avoid guesswork. Document when the light appears and whether throttle or load triggers it. Then check for vacuum leaks and wiring strain. If codes are unreadable, follow the quick mechanical checks below before swapping parts. [Elektroda, miki1203, post #16827048]
Why would it run in reverse but stall going forward?
When you select reverse, the powertrain shifts in the opposite direction. That motion can tug vacuum hoses or stressed grounds, temporarily restoring or worsening a connection. As one expert noted, it can even expose a torn engine ground strap. Inspect the brake servo vacuum line, MAP hose, and engine ground while rocking the engine. Movement-sensitive faults explain direction-dependent symptoms during acceleration. "It may just as well be a torn-up engine mass switch." [Elektroda, tzok, post #16827895]
Can the brake servo vacuum hose really cause stalling?
Yes. A cracked or loose servo vacuum hose becomes an unmetered air leak. That leans the mixture during throttle, causing hesitation or a stall. Because braking and engine load vary together in traffic, you may see intermittent symptoms. Flex the hose while idling and listen for pitch changes. Check the one-way valve orientation. Replace any hardened or split sections. Confirm by temporarily isolating the line per the How‑To below. [Elektroda, andrzej20001, post #16827512]
What’s the first diagnostic step when the injection light comes on?
Read the ECU fault memory. The controller turns the light on to point you to a specific sensor or system. It retains errors even after power loss, so you won’t erase clues by disconnecting the battery. "The controller itself informs the control that something is wrong with one of the sensors." Capture codes at the moment of failure if possible. Then test the implicated circuit rather than replacing parts blindly. [Elektroda, sandamiano, post #16827312]
I don’t have a scanner—what quick checks can I do today?
Perform targeted mechanical checks: inspect and reseat the brake servo hose at the intake. Temporarily disconnect the servo from the manifold and plug the port to rule out a vacuum leak. Wiggle-test the MAP sensor lead while idling. If symptoms change, repair the wiring or hose. These checks cost nothing and can confirm a vacuum or harness issue before you book diagnostics. [Elektroda, mario 77, post #16828551]
Could a crankshaft position sensor cause these symptoms?
Yes, a failing crank sensor can cause sudden cutouts or no-starts, especially when hot. However, your thread’s direction-dependent behavior suggests movement or vacuum issues first. Test sensor signal with a scope or substitution only after code reading. Avoid replacing on speculation. One user suspected this sensor here but the confirmed fix differed. Prioritize faults flagged by the ECU. [Elektroda, miki1203, post #16828386]
What is the MAP sensor, and why does its cable matter?
The MAP (Manifold Absolute Pressure) sensor measures intake vacuum for fuel and ignition calculations. A loose hose or damaged cable feeds wrong load data, causing lean spikes and stalls on throttle. Inspect the small vacuum hose and the sensor’s electrical connector. Clean and reseat both ends. Repair any cracked rubber or chafed wires before further testing. A quick wiggle test can expose intermittent faults. [Elektroda, mario 77, post #16828551]
What ultimately fixed the original poster’s Seicento?
The OP reported an ECU failure and resolved the issue after addressing the computer. That is the only confirmed outcome in this discussion. Keep ECU power and ground integrity in mind during diagnostics, since weak supply can mimic module failure. Verify basics before condemning the unit. If codes and tests implicate the ECU, seek repair or replacement. [Elektroda, miki1203, post #16853742]
How do I quickly check for a brake servo vacuum leak?
Try this three-step check:
- Warm the engine; set the parking brake.
- Disconnect the servo hose at the intake and plug the manifold port securely.
- Blip the throttle; if hesitation disappears, repair the hose/check valve/servo.
Perform a road test carefully once reconnected. Replace brittle hoses and verify one‑way valve function. This isolates a major unmetered air source in minutes. [Elektroda, mario 77, post #16828551]
Can a kinked fuel return hose cause hesitation or stalling?
Yes. A bent or pinched return can alter rail pressure and upset fueling during throttle transitions. One forum user reported a similar case traced to a bent return hose. Inspect the full run of supply and return lines for kinks near clips and the tank. Straighten or replace any restricted sections and retest. This is a low-cost, high-impact fix when present. [Elektroda, deezoo68, post #16827100]
Could a bad engine ground strap cause cutouts on acceleration?
Yes. A torn or corroded engine ground can intermittently drop ECU and sensor reference grounds under torque. That causes misfires, stalls, or random warning lights. Inspect the ground strap between engine and body. Clean both lugs and reinstall tightly. Flex the harness while idling to reveal movement-related dropouts. Replace any frayed strap you find. [Elektroda, tzok, post #16827895]
What is the brake servo and how is it connected to the engine?
The brake servo (booster) multiplies pedal force using engine vacuum. A hose connects the intake manifold to the servo through a one‑way valve. Any crack or disconnection becomes a vacuum leak, leaning the mixture and destabilizing idle. That can trigger hesitation when you add throttle. Ensure the hose seats firmly and the valve faces the correct direction. [Elektroda, tzok, post #16827863]
Two users told me to read codes—do I really need to?
Yes. Forum guidance emphasized code reading because it targets the failing circuit. Skipping this step leads to parts darts. As one member put it, just read the logs and decode the errors. Capture codes during the fault event for the best clues. Then test that system methodically. "It will be known immediately what the kaman ..." [Elektroda, web69, post #16828153]
Is an ECU failure common, and how do I confirm it?
In this thread, one user confirmed a failed ECU; others proposed hoses, grounds, and sensors first. Confirm ECU faults only after verifying clean power, grounds, and signal wiring. If codes persist with correct inputs and outputs, the ECU may be defective. Professional testing or substitution is the proof step. Avoid premature replacement. [Elektroda, miki1203, post #16853742]
Edge case: the tube angle toward the windshield—could that matter?
A misrouted or tilted hose/tube can kink under engine movement, creating a sporadic vacuum leak. If reversing changes the tilt, symptoms may appear directionally. Reseat the tube, ensure smooth bends, and secure with proper clips. Re‑evaluate acceleration response after correcting routing. This matches the thread’s movement-sensitive theme and is quick to rule out. [Elektroda, tzok, post #16827895]
