My suburban won't start.

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brianblanton

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I have a 1995 chevy suburban. It is 2 wheel drive, 5.7 tbi. I have added a 1 inch lift plate between the tbi and the intake. It ran just fine for about 3-4 months after installing the lift plate. I rebuilt the tbi, and added a 14 psi spring. It gave me a lot more torque from the engine at low speeds. It was running yesterday, no problem. I went out to start it up this morning, and it sprays from the tbi injectors, it cranks but won't start. I have replaced the fuel filter this morning, and it still doesn't start. I have removed the relay for the fuel pump, and it turns over ok. I replaced the relay, and it try's to start, I just won't continue to run. Any help would be greatly appreciated.

Sorry. I have replaced the cap, ignition coil, wires. Left the old spark plugs in because I replaced them 3 months ago. I haven't checked the pcv valve. I will do it today. The problem is that it is an OBD1 computer, NOT OBD2. I'm not sure how to hook up my fuel pressure sensor. I used to own a 2003 silverado. Is there any place on my 5.7 liter to hook it up? Oh, BTW I ordered a spark checker from amazon. :)
 
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someotherguy

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Basics on no-starts are checking fuel pressure and checking spark.

Since you say it is spraying from the injectors and attempts to start but won't stay running, low fuel pressure is a possibility. Another one outside of the pressure and spark concerns would be a bad coolant temperature sensor (CTS) causing the mixture to be too rich and stalling out the engine because it's fuel-fouling the plugs.

There's a small tool investment to be made here. A decent fuel pressure tester that can work with a TBI engine will set you back less than $50 or so; a multimeter you can use to check the CTS should run you about the same (you don't need to spend megabucks on a fancy one), and a spark checker tool is pretty cheap from any auto parts or tool store.

Are ya ready? My best guess on plan of attack would be, I'd start with checking the CTS. If it comes back in range, I'd move on to fuel pressure.

Richard
 

someotherguy

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And ya know, now that I think about it, since you were messing around with the throttle body adding your spacer plate and adjustable regulator.. check your MAP sensor vacuum connection at the rear of the TBI. If that isn't a tight fit or if it has slipped off, that could be an issue. In reality it should run with the MAP completely disconnected, it just won't run well. Easy to check, anyway.

Richard
 

Schurkey

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Basics on no-starts are checking fuel pressure and checking spark.
Agreed, as long as we're talking about "cranks, but won't start" rather than "won't crank". That seems to be the case here.

Since you say it is spraying from the injectors and attempts to start but won't stay running, low fuel pressure is a possibility. Another one outside of the pressure and spark concerns would be a bad coolant temperature sensor (CTS) causing the mixture to be too rich and stalling out the engine because it's fuel-fouling the plugs.
Also agreed.

How old are the usual "tune-up" items--cap, rotor, plug wires, spark plugs, air filter, PCV valve, etc.

Another possibility is weak spark due to failed ignition coil, or improper signal from the pickup coil or ignition module.

There's a small tool investment to be made here. A decent fuel pressure tester that can work with a TBI engine will set you back less than $50 or so;
Or get one from a parts-store "loaner-tool" program. You buy the tool from their stock of "loaners", use it, return it for a refund. Essentially "free".

One hopes that the gauge is accurate, and that they have a TBI adapter. The TBI adapter may be the sticking-point with a loaner-tool.

a multimeter you can use to check the CTS should run you about the same (you don't need to spend megabucks on a fancy one),
Not a fan of testing sensors with a multimeter. Yes, it can be done. It generally does NOT verify the wire harness the sensor is connected to. And it's a complete pain in the tuckus. In little more than the time it takes to verify one sensor with a multimeter, you can verify ALL the sensors, and their wire harnesses using a scan tool; and you don't get messy under the hood, or risk damaging sensor connectors.

and a spark checker tool is pretty cheap from any auto parts or tool store.
Should be in everyone's tool box. I consider a spark-tester essential.

I prefer this kind; there's two versions and several brand-names. There's the ones calibrated for HEI ignition systems, and the kind with a smaller air-gap that are intended for points or low-energy electronic ignitions.

www.amazon.com/dp/B003WZXAWK/?coliid=I3S98D7T1J0RLJ&colid=2VLYZKC3HBBDO&ref_=lv_ov_lig_dp_it&th=1
xc_hide_links_from_guests_guests_error_hide_media

There's also other designs, some with an adjustable air gap, and some that just blink a light-bulb. You want a tester where the spark actually jumps an air-gap, not one where the spark just flashes a lightbulb.
 

brianblanton

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I found out that my fuel pressure is running at 11 psi, and it is fluctuating 10.5 to 11.5 psi. That means that I need an add on fuel pressure regulator. I ordered one from amazon, and it got here ok. I do need to know, however, whether to splice inline with the small return line to the fuel tank. I need the fuel pressure regulator to return to the tank, but I am wondering if the tbi should return to the tank on the same line, or whether I need to run an additional line to the fuel tank. I also need to know which is the supply line and which is the return line. In my opinion, the large (3/8 inch) is the feed line, and the smaller line is the return line. Please correct me if I am wrong. Thanks for any information. Your suggestions before helped me a lot with my engine diagnosis.
 

Schurkey

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I found out that my fuel pressure is running at 11 psi, and it is fluctuating 10.5 to 11.5 psi. That means that I need an add on fuel pressure regulator.
Why would you jump to that conclusion?

This could be a matter of insufficient power to the fuel pump, including an insufficient ground.
It could be a worn-out fuel pump.
It could be a plugging fuel filter--either in-line, or the sock on the bottom of the pump.
MAYBE, it could mean a defect in the existing pressure regulator--but I think that's unlikely.

Cramming another fuel pressure regulator in-line with the existing regulator is unlikely to be a proper fix.
 

brianblanton

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172,000 miles. I am putting in another fpr because the fuel pump is outputing 10.5 to 11.5 psi. I looked at another carborated pickup and it showed 6 psi. Very steady, no jumping around.
 

Schurkey

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I am putting in another fpr because the fuel pump is outputing 10.5 to 11.5 psi.
Your PUMP should toss 15+ psi, dropped by the regulator to whatever the regulator is set at. The regulator does not change pressure from 10.5 to 11.5. The regulator is set at ONE pressure. If the pressure varies, it's probably because the pump's output pressure has dropped due to wear or voltage/current problems.

You're probably "fixing" the wrong thing.

I looked at another carborated pickup and it showed 6 psi. Very steady, no jumping around.
Electric fuel pump, or engine-driven? If it's engine driven, the fuel pressure pulses like mad at low engine speed. If it's electric, then steady pressure would be normal and desirable; but you need more pressure than that for TBI.
 

Donald Mitchell

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The regulator on the tbi is where you replaced the spring. Fuel pump, or bad ground at the fuel pump. Was it a stock spring or something else?
 
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