How To Check Fuel Pressure

how to test fuel pressureI have a Chevy S10 Blazer and after a trip I arrived back home and casually turned it off. When I tried to turn it back on, it turned but there was no response. I then went to a next door neighbor who is a mechanic and he said the biggest problem would be the fuel pump.

He hit it once with a hammer and on cranking the car it started. So we deemed the problem to be the fuel pump. I replaced the fuel pump myself and it now turns on when the key is on the ON position and the fuel lines are pumping fuel. (I checked it on the engine.) But after I replaced the fuel pump and checked that it was pumping fuel I tried to start the car and it gave the same response. So it turns over but just won’t start.

I have since checked the spark plugs and they seemed to produce spark. (I checked them by opening the wire connecting to the spark plug sticking a screwdriver inside and touching the metal part to a “ground” like the top of the engine, and it produced sparks) So what could be the problem now? What could cause the engine to not start after the fuel pump has been replaced and the spark plugs checked?
-Please respond,

Howdy there Abel,

I am not sure I understand your email, BUT the first thing I would do is check the fuel pump PRESSURE. The pump might be pumping enough fuel into the lines that you can see it, but if it is not pumping hard enough the engine won’t start.

There is a place to check fuel pressure on the back of the engine with a manual screw on gauge. Hitting the tank with a hammer is a great and easy test to kick start a weak pump, but not a very accurate test. Could it have been coincidental? Maybe just the time it took to get the neighbor solved the problem and when he hit the tank you guys just assumed it was the pump?

Video showing you how to test the fuel pump pressure with a manual gauge

Checking spark the way you did is ok, but it does not tell you if the spark was strong enough to ignite the fuel, it just tells you there was some kind of spark.

I would check fuel pump pressures and recheck your installation. If you used a cheap aftermarket splice in pump, I would be suspicious. Can you hear the pump prime itself when you turn the key to the on position? Are you sure the pump was installed correctly?

I would also check the spark from the ignition coil, and test the ignition module.

Please share this with your friends,

Austin Davis

Posted in: Won't Start Issues

48 Comments on "How To Check Fuel Pressure"

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  1. Jennifer Valliant says:

    Having problems with my car not starting. The first time this happened changed caps coil packs ICM. Has new plugs and wires. Got started running perfectly. Then wouldn’t start again had it to shop messed w some wires wouldn’t start. Next morning its not so cold out mechanic checked to see if it start starts right up so took car home n won’t start again. I’ve tried starting it with jumper cables still don’t start. It turns over just won’t fire. Fuel pressure measures fine. If battery is weak and not signalling the ICM should would jump starting not always work?

    • Austin Davis says:

      These types of problems are hard to track down, since they are intermittent. You need to determine what is missing…fuel pressure or spark. A manual fuel pressure gauge attached to the back of the engine taped to your windshield while you drive, might at least rule out a weak fuel pump. Using a “node” light attached to a spark plug wire then tapped to your windshield as you drive will help rule out lack of spark. Getting a better mechanic is also advised, one with more technical knowledge of these types of problems. But, they still need it to “fail to start” while they have test equipment hooked up to it.

  2. Woody says:

    Have a 2000 blazer used the guy told me that the fuel pump is new,but when it is running i get the evap code found vent hose

    pluged with a spark plug hooked it back to purge valve. Now when running gas is running out of purge valve.Changed gas canister no good still leaking, was thinking gas fuel pump is wrong type. Thanks

    • Austin Davis says:

      I think you still have a “vent” issue. I know on the full sized trucks they have a huge problem with their canister vent valves, but not real sure about the trailblazer. I would remove the gas cap and run the vehicle to see if you still have fuel drumping into the purge valve, if not you have a vent issue somewhere. Vent hose to the fuel tank, canister fuel vent valve, pinched vent hose etc. etc.

  3. dennis duray says:

    Ive got a 2001 blazer came out of work and had no power jumped it and started right up left it run for 20 minutes when i got home 2 hours later it theres no power again can someone help

    • Austin Davis says:

      Always start with a new battery or a known good battery, clean AND tight battery cable terminals. If you still have issues, need to check the alternator output, check for a voltage drain (something electrical left on or sucking battery power with key off), check ground connections.

  4. jessie says:

    try the spider injectors they have a tendency to over heat and seal shut the new one has a built in cooler they are operated by the timing of the motor so make shore it didn’t jump time as long as it has an orange spark when you test the coil its fine.

  5. Bryan says:

    I have a 2000 s10 4.3l. Cranks bury won’t turn over. Thought it might be the fuel pump but i put a charger on the battery and it will start right up. Can someone help me here.

    • Austin Davis says:

      So it starts when you put the charger on the battery every time? Could it be just a weak battery not spinning the engine over fast enough or providing a strong 12 volts to the computer? Try a new or known good battery and see what happens.

  6. Monique says:

    I have a 98 a blazer I changed the fuel pump,module,and coil.It cranks but won’t start

    • Austin Davis says:

      I would start by checking for spark to all spark plugs, checking fuel pressure at the engine with a manual fuel pressure gauge, check cylinder compression and firing order. If this is a 4.3 v6 you might be losing fuel pressure (and have a raw fuel leak, and smell) at the back of the engine. The “spyder” fuel injector can leak raw fuel, thus causing low fuel pressure…enough to keep the engine from starting. Look towards the back center of the engine, follow those hard plastic rubber fuel lines, see any leaks, smell any fuel? They used to make a repair kit for it, but you might be better off buying a new injector, if that is the culprit.

  7. reggie says:

    Hello my 2001 chev blazer wont start i have replace spark plugs ,fuel pump . It turn over but wont start. Somebody said it may b the camshaft i dont kno. Please help

    • Austin Davis says:

      Well, you need to be able to test for spark to the spark plugs and fuel pressure at the engine to find out what is missing…fuel, spark or lack of compression. If you can not do that yourself, I would advise you pay a mechanic to help you diagnosis the problem (which is ALWAYS cheaper than guessing and replacing parts)

      Could be lack of spark, like a ignition coil or ignition module type of problem, or many other things. Things are just to complicated these days and you have to do some troubleshooting and diagnosing.

  8. Danny says:

    Love your ideas, going to try them out now and see if I can figure out what is going on.

  9. Ryan says:

    thanks for the information i will try that out and let you know what i find out

  10. Ryan says:

    I have a 1997 chevy blazer that will start then die at times and not start back up it will crank but not fire i have noticed that when it is cranking and not starting that my dash gauges do not work but once they start to work then my blazer will start right up i have replaced fuel pump and also when my gauges are not working neather does my fuel pump i think its sumthing electrical but i am not sure dose any body have any advice

    • By Austin Davis says:

      Hi there, yes this could be related to the gauges. I would probably start looking at the ignition switch first. Look under the steering column, usually a fairly large white looking component attached to the column. See if you can wiggle it and the connections and get the gauges to come on…or replace it and see what happens.

      If those gauges are not coming on you are not getting power…my best guess anyway from this side of the computer. 🙂

      keep me posted.

  11. Aub says:

    Thanks Austin. I determined the ICM works like this:
    1. When cranking the crank signal (3 Amp fuse) to the ECM keeps the B lead low. This puts the ICM in Bypass or limp-home mode.
    2. This will cause the ICM to generate pulses directly to the Ignition coil, and R lead pulses to the ECM.
    3. The ECM seeing R lead pulses from the ICM will pulse the Injector. This should fire up the engine as the ECM has also turned on the fuel pump providing fuel pressure for 2 to 3 seconds at the turning on of the ign key.
    4. When the Ign Key is released causing the crank signal to go low, the ECM brings the B lead hi (+5 Volts) which causes the ICM to receive spark timing pulses from the ECM via the E lead.
    5. The fuel pump relay is held on by the oil pressure switch in run mode.

    I found that strangely enough, the engine would fire up after I had “tickled” one of the ICM to ECM leads (B or R) with my analog multimeter when trying to measure signals. This was likely caused by a poor ground in the ICM which needed some current to clear. The engine would then usually fire up normally until left to sit for a few rainy days again.
    I replaced the ICM. Hopefully this is the end of my problems.

  12. Aub says:

    1991 S-10 4.3 v6, I have a similar problem. No spark on cranking engine if truck left sitting for a few days and it is wet. When it starts I have gone on hundred mile trips without problems.
    Test light shows no signal at B lead (tan) from ECM to Ign Module. This is supposed to be the cranking ignition pulse or limp home mode from the ECM.
    Question: Does the ECM look for fuel pressure before allowing ignition spark?
    Guessing and parts replacing got me into trouble. I replaced the Fuel Pump relay and the new after market one failed and really put me behind the eight ball. Also banging the fuel tank seemed to fix it once.

    • By Austin Davis says:

      Well, the ECM is not looking for fuel pressure from the pump, but is getting…or waiting for a crank signal from the distributor.From what I remember, this distributor should be able to produce spark with out the EMC, and the B lead is a bypass wire from the ECM.

      So, I would start with checking distributor cap, rotor, power and grounds etc. But you should have spark without the ECM. There should be pink wires at your ignition coil, those are hot wires..power wires. If you don’t have spark from the distributor after checking secondary ignition items then I would guess at a new ignition module.

  13. kenny says:

    Just so everyone knows the pick up wire also controls spark to the ignition modgel also which intern fires the coil which fires the spark wires so if ur fuel pump is kicking on I bet its the pickup wire I looked on things people where telling me ignition modgel they said fuel pump coil wires plugs and the funny part a Guy that lives next door that’s in his 80’s use to work for GM on the distbutors he had the parts in his garage I didn’t believe him that it was the pick up wire he said trust me I built GM cars for 30+ years I put it in put the disbutor. Acid in turn the key and it fired right up now when it went out it back fired then died started up once then died and never started till 200 dollars later I get a free part from a retired GM worker and it fires up so I learned a valuable lesson look it up ask a lot before playing a guessing game or take it to a real mechanic not a shade tree one and get it fixed

  14. kenny says:

    If ur injectors also don’t spray could be a pick up wire in the disbutor to do this it must be pulled out and taken apart part replace then put back in I mark my distbutor just so I know where it goes back in. The pickup wire do send a signal to the ecm to fire the injectors just so people know for the tbi motors

  15. Joey says:

    i have a 02 chevy 10 blazer with the 4.3. I do not get a spark at any spark plug. We have changed out everything that has to do with the engine starting and the plugs and ran every test possible and checked wires with voltmeter and the plugs with the nano light tester. But it still doesnt get spark….My friend said it might be the computer that needs to be replaced. The fuses are fine and we cant think of anything else serioulsy….We ran a diagnostic in the fuse panel inside with a reader and nothing came back. It will crank but no spark, all the plugs r new and everything has been checked. Does anyone have any other ideas.?

    • By Austin Davis says:

      Humm, 2002….so you have a distributor correct? if so, then I would first start by testing the external ignition coil. remove the coil wire, and try and ground the end of the coil wire to a metal part on the engine and have someone crank the engine over to check for spark. if no spark from the coil, replace the coil. if there is spark then I would remove the distributor cap and check the cap and ignition rotor…or just replace them. You should have an ignition module, which is located near the ignition coil. There are many complaints about their failures and will cause a no spark issue when they fail.

      There should also be a crankshaft position sensor near the harmonic balancer pulley, which is the lower large pulley at the bottom of the engine. Crank sensors are notorious for failure, but rule out the easier stuff first.

  16. joseph says:

    I have a 94 blazer s10 vin w. Its been sitting for like 6 months and it would not start. So I change the spark plugs fuel pump and It started up and ran for 4 days then cut off. I have compression from the spark plugs my fuel pump is turning on my relay and everything’s working all my fuses are good. I got a brand new distributor it is a gm 23. and for some reason I feel pressure is only 12 to 13 ps i’s and yes I know that is not right trust me 41to 55. Firing order 1-6-5-4-3-2. If someone could get back with me I would really appreciate it

    • Austin says:

      And you still have spark at each spark plug now? If you are reading 12-13 PSI at the fuel rail under the hood, that is too low and I can only suspect you have a fuel pump issue or a problem inside the fuel tank. I have seen a few stopped up fuel pump screens, and have seen a few broken plastic hold down clamps that hold the pump to the fuel tank. This allows the pump to move around the tank and bang into the tank, which kills it. Might want to replace the fuel filter first before you pull the tank down again.

  17. Thomas says:

    i have a 1992 chevy s10 blazer with the 4.3 vortec. i was driving and it died at a stop light and now cannot get it to start back up. had module tested, coil tested, rotor is spinnin but no spark. where do i start to look next?

    • Austin says:

      Are you sure about no spark??? These vehicles are suspect of bad fuel pumps, so I would check fuel pressure at the engine next to rule that out. Sometimes you can bang on the bottom of the fuel tank with a block of wood AS someone is cranking the engine over. This can jump start a weak fuel pump. Testing for spark should be done with a nano light tester which will flash when spark is present. Check for spark at each plug. But spark can be missleading if there is no fuel injector pulse. I would rule out lack of fuel pressure first.

  18. blazertommy says:

    I have a 1990 blazer and it is hard to start every time. It also revs way up every time you crank it wether it’s crank it cut it off and start it right back or wait hours in between. Any Ides, im getting tired of wondering if this thing is going to crank every time.

    • Austin says:

      In most cases one of the following is to blame

      1. Bad fuel pressure regulator
      2. Weak fuel pump
      3. Bad fuel injector
      4. Bad idle control valve
      5. Vacuum leak under the hood somewhere

      I would first start with checking fuel pressure at the engine with a manual fuel pressure gauge and go from there. You most likely have a “spyder” type fuel injector which is one big injector with a bunch of small plastic tubes feeding each cylinder fuel. These injectors leak fuel usually at the back of the intake manifold causing a drop in fuel pressure and hard starts. Once the engine starts it takes a second or two to burn off the excess fuel causing the fast idle speed.

  19. camelTl247 says:

    john with the 1999 S10 Blazer……….had a friend w/the same prob and it was the fact alrm the bran box had to get it fixed at the dealer

  20. camelTl247 says:

    1,2,3 all good the alrm light keeps falshing on the dash it starts then cuts right off

  21. camelTl247 says:

    02 chev,s10 2.2L no start i know the prob but not sure how to go about fixing it it has alot to do w/the fact alrm cutting off the fuel at the injetors……….what color is the ground wire that i need to hoor up fram ground to

  22. veronica says:

    I have spark and gas going to it and it won’t start turns over but won’t start? I have an 01 Chevy Blazer.

    • Austin says:

      You need 3 things

      1. Spark to ALL spark plugs
      2. Proper fuel PRESSURE, not just a trickle of fuel
      3. Compression on all cylinders

      These vehicles have a history of weak fuel pumps and leaking fuel injectors. I would suspect you do not have enough fuel pressure if you have spark and compression. Bang on the bottom of the fuel tank with a rubber hammer or block of wood AS someone is cranking the engine over. If it starts you most likely need a new fuel pump inside the fuel tank.

  23. John says:

    1999 S10 Blazer will sometimes start and run for 1-2 seconds then die. After waiting EXACTLY 10 minutes, it will start every time. Anyone with similar problems?

    • Austin says:

      Would be awesome if you could get your mechanic to check for spark and fuel during this no start time period. My first instinct is lack of fuel due to a fuel pump problem which is fairly common on these. Sometimes banging on the bottom of the fuel tank with a block of wood as someone cranks the engine over can jump start a weak fuel pump.

      If you do not have spark going to the spark plugs you could have an ignition module or ignition coil issue. You are missing either spark to the plugs or fuel pressure, so try to rule one out.

  24. tory says:

    I had the same problem as Bryan no lights, I did the same, hit the steering wheel lights came on and it started… turns out it was a short in my switch wiring!!

  25. HuieJay says:

    hey i had the same problem change your sparkplug wires mine were shorting out i changed my fuel pump and that wasnt it everyone told me it was but my wires had a short and were grounding now its back in acting and it would have saved me like 200 dollars

  26. Bryan says:

    have the same problem the lights never came on and I use to get really mad and I gave the steering wheel a smack or two and the lights would go on. I’ve been doin that for almost a year and I know its not good. WOULDNT A GOOD IDEA BE TO GET A REMOTE STARTER????? would that work Im not familiar with those things much

  27. jimmer says:

    replace the ignition module first dont be confused by the ecm electronic control module also known as the computer but check all conections first and the battery must be good

  28. zach - Answer says:

    Oh, two more things:

    1: if you have a tbi you can pour a little fuel in the top and try to start the engine. If it starts, your problem is in fact fuel.

    2: if fuel is coming out of injectors, but it is very weak, it could be a weak fuel pump, clogged up fuel filter, pinched fuel line, or fuel pressure regulator (located just previous to the fuel injectors).

  29. zach - Answer says:

    I had this problem and found the solution. I had a TBI but it may not make a difference.

    First thing check all fuses.

    After that, first, fuel must pump out from your injectors. Verify this is happening by putting a cloth or paper in front of an injector and try to start the car. If fuel came out of the injector, fuel is probably not the problem.

    If fuel did not come out, next check to see if fuel is even making it up to your injectors from the tank. The way I checked that is to disconnect the fuel line from the back of the engine (which lets out any fuel sitting there). Then re-connect it, and attempt to start. Then disconnect it again and see if new fuel falls out of the line again. If no fuel comes out, either no fuel is pumping out of the tank or your line from the tank to engine is clogged. Most likely it is your fuel pump failing in some way. Look up how to deal with that (not hard).

    If fuel does come out, fuel is at least reaching the injectors. If it is your injectors, first thing to check is if they are getting the signal to inject the fuel. This can be verified by testing the injector pulse with a $3 test light. (look up that sentence for exactly how to do it – not hard). If they fail that test, you have some kind of computer/sensor/electrical problem and further testing is needed to narrow that down.

    If they pass that test, then they are probably stuck/clogged. People clean these things, etc, but it’s very hard and doesn’t give you a new injector, just a clean, old one. So in my case I just bought and installed new injectors at this point and it started right up perfect.

    Hope that helps!

  30. joe says:

    really? take it to a mechanic?! Great car advice website mac.

    • admin says:

      ummmmm, ya. Did you actually read the reply I gave to the original email? DId you happen to read how many items the owner has already guessed at and figure up the cost that has already been spent on GUESSING? I would bet its at least $200 in parts cost….not including his time to actually do the work. So my LAST followup suggestion after he had already done what I first suggested him to do was to go to a qualified mechanic and stop guessing. You can get a mechanic to diagnose the problem for you and you can go home and do the work yourself but stopppppppppppp guessing!

  31. David says:

    I am having the same problem in my 93 blazer, i have tested all of the same things and replaced those and more, but my blazer is still not starting. Any help would be appreciated


    • admin says:

      Sorry for my delay, have been on vacation all week. Spent $100 and get a qualified mechanic to diagnosis this for you….trust me it will be cheaper in the long run.

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