Sputtering, backfiring, hard start, engine light, slow accelerating

LDWILSON

MEMBER
1991 MAZDA
3.0L
6 CYL
2WD
AUTOMATIC
58,000 MILES

On first start I need to prime by turning on fuel pump only three to four times and then maybe depress pedal once to start and may have to this more than once. This has been a problem for a while. Now, once it starts and in park it seems smooth running. Once I depress the gas it can bog and has even died. Replaced fuel filter and it helped somewhat but still slow acceleration, but once rolling (fifty five) it maintains and seems okay until I accelerate more. After first start, subsequent starts are easier if engine is still warm. Had some work done on exhaust system but there is still a leak (loud) towards the front. Did an STP fuel injector treatment today, cannot tell yet if it helped. The check engine light comes on after about fifteen minutes operation under normal operation. Do not notice it as much on highway. It runs good aside from the recent sputtering. Vehicle sat for sometime (year plus) and I recently replaced transmission. Do not have the funds to take to garage so any input would be greatly appreciated. Thanks in advance.

3 Replies

STEVE W.

MECHANIC
13,498 POSTS

It sounds like a case of low pressure from a failing pump or bad regulator. The constant need to prime as well as the poor acceleration are from it starving for fuel.

First check the fuel pump pressure itself. Connect a fuel pressure gauge to the line coming from the pump before the pressure regulator and see what it shows for pressure. (Should be around 30-40 psi minimum with the engine running at idle)

Test the regulator next, disconnect the vacuum line and see if there is any gas in the line ore coming out of the fitting. If yes the diaphragm has failed and you need a new regulator. If no gas in the line connect a pressure gauge inline between the regulator and the injectors and watch the fuel pressure as you remove the vacuum line. It should change if the regulator is working.

I think you will find low pressure, unfortunately the pump is in the tank. It is not that hard to change but it is not that fun. There should be a video or two online, but you did not state which model it is so I cannot link you to one.

Post back what you find after those tests and we can determine if it is the pump/regulator or something else.

Sputtering, backfiring, hard start, engine light, slow accelerating

3 Replies

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