Ask Xulfiqar - An Automotive Encyclopedia

[abdullahzahid625]

Thank you

[helper_learner]

Read it, https://byjus.com/question-answer/on-heating-a-conductor-its-resistance/

[Xulfiqar]

The main relay is a double relay that powers the fuel pump and also the injectors etc.

Its failure is a very known issue

[abid110]

@Xulfiqar I recently bought a City 2016 manual transmission 95k KMs done. car is Alhamdulillah very good. however, one issue is very irritating which pops up all by itself all of a sudden and that too very rarely - say once in a 100 times of driving - and sometimes twice in a km of drive - means it is coming up intermittently. everything runs fine, suddenly the brake pedal gets super hard and car seems to be slipping towards right and steering turns towards right side too. even if i pump the brake pedal it keeps on super hard and car keeps on brutally slipping. brakes are services twice in detail, calipers, pads all are ok, showed it to brake booster wala, he checked everything and said its ok after running the car very fast and braking hard and confirmed all is ok even ABS engaging perfectly fine - please note the issue never came up in front of technicians whenever they test drove it. i need your assistance in exact solution to this issue please. my city is karachi.

[pwuser166331039855]

Most probably either brake booster or Master Brake Cylinder needs replacement.

Since Brake booster works with Engine’s Vacuum system, so maybe it sometimes miss to receive the enough vacuum from engine which makes the brake pedal hard.

[abid110]

Most probably either brake booster or Master Brake Cylinder needs replacement.

Since Brake booster works with Engine’s Vacuum system, so maybe it sometimes miss to receive the enough vacuum from engine which makes the brake pedal hard.

i was suspecting the same however 3 mechanics turned down this fact. the issue never came up when they test drove it. what about car slipping to the right side when braking when the same problem comes up - very sharply as if car is floating on wavy water (the feeling is same this).?

[pwuser166331039855]

I didn’t reply to car skidding since I was also waiting zulfiqar’s reply on it

[frontagencies]

Zulfiqar is the best expert. I am reading his comments for years.

[k180233]

So update on this, this time the issue came up in front of my main mechanic which has worked on this car since I bought. I am listing down his diagnosis procedure, let me know if his diagnosis looks acceptable to you

Issue: No start, but engine cranking.

Things checked:

1. Checked Spark, it was there
2. Checked power to injectors, it was there
3. Checked pulse to injectors, it was there
4. Checked fuel at the return line, it WAS NOT there at the time of cranking. It was in the main line connecting to injectors rail, but not in the return line.
5. We checked for power at the fuel pump when we turn the switch on, power was there fine for 2 seconds.
6. I did ask him to check main relay, he did and said it was fine, also he said it was the first thing he checked when I previously reported this issue to him and he repaired it back then.

Here's what he thinks, as the battery in the car is of smaller size than recommended for this car, he says the voltage at the time of cranking drops which result in low fuel pressure from the pump, hence my usual long cranking starts. He says 1 or 2 long cranks, and voltage from your battery is totally done to power fuel pump enough for the required fuel pressure, he also said that there might be a possibility that sometimes it gets so low that it is not even enough to power the ECU properly.

We tested this through drawing load from battery and checking voltages at cranking.

1. Fully charged battery, car starts fine but with a bit longer crank
   a. Voltage at switch on: 11.8V
   b. Voltage at cranking: 8.8V

2. Drew power from the battery by applying load through a battery load tester for 3-4 seconds, now car wasn't starting.
   a. Voltage at switch on: ~8-9V
   b. Voltage at cranking: ~6-7V

3. Again drew power from the battery by applying load from 3-4 seconds, again the car doesn't start this time
   a. Voltage at switch on: ~7-8V
   b. Voltage at cranking: ~5-6V

So we have changed the battery to the recommended size, and the long crank does appear to have gone now, car starts in a 1-2sec crank now. Will update if the issue ever comes up again. But my question is the above diagnosis right? Is it possible that such low voltage can result in fuel pump not working properly or ECU not powering up properly? Unfortunately we didn't have a fuel pressure gauge to get an exact reading though.

Thanks for the help @Xulfiqar

[Xulfiqar]

6V while cranking?

The ecu shuts down below 8v

Lol

[k180233]

Lol, makes total sense now why sometimes even the injector pulse disappears.

Also can low voltage result in fuel pump not pressuring fuel rail enough causing long cranks?

[Xulfiqar]

Yes the main relay coil also shuts down under 8v, the pump is wired through the main relay.

[dayrider]

Basically one tire locks up. Get your brake oil changed, and get the caliper pins checked

[abid110]

@dayrider this happens very rarely - not frequent - but whenever it happens, its so scary as car fails to respond to brakes and sharply moves towards right. calipers are checked thoroughly and seemed fine as per 2 mechanics. i am unsure what to do now...

[dayrider]

When did you last change your brake oil

[abid110]

When did you last change your brake oil

i dont know, i bought it at 93k km mileage, its 96k now.

if its brake oil issue, why it performs ok 99.9% of the time? also, can it be related to vacuum of booster/master cylinder issues?

[pwuser166331039855]

can it be related to vacuum of booster/master cylinder issues?

i guess yes it can be one of the possible reasons.
Brake boosters usually have very long life and works with engine's vacuum. sometimes some rubber pipe develop a crack or minor leak or loose joint, and hence affects the performance.

[abid110]

i guess yes it can be one of the possible reasons.Brake boosters usually have very long life and works with engine's vacuum. sometimes some rubber pipe develop a crack or minor leak or loose joint, and hence affects the performance.

thankyou for reply. what can be done in this regard? the pipe visually seems all ok and perfectly tight

[dayrider]

Replace the brake oil, a flush in the system will remove any discrepancy

[pwuser162360148780]

I have a question I am trying to wrap my head around a car purchased recently suzuki hustler non turbo variant.

When it passes 50 to 60 on 4000 RPM to 5000 RPM it feels like the car is swinging. It goes forward and then stops and then starts going smooth again and feels like shifting to next gear.

One more thing, The engine is driven 170,000 Km, sometimes when the car is complete idle I cannot pass small speed breaker even when flooring the gas pedal, it feels like it is not moving at all and then eventually turning the ac off it goes forward very slowly.

I have tried changing sparks, done fuel pump change, did basic tuning and general tuning. did compression test, 105, 140, 140 respectively in the valves from left to right, I am thinking of doing engine flush with liqui moly to get the compression up.

Furthermore the oil that is being used it is 10w - 40. Transmission oil is fine as well.

One mechanic said that it's gear needs replacing. Can you please see and tell me what could be the issue here?

No engine check lights are coming up also