Mercruiser 5.0 TBI hesitation at WOT

[DollarBoat]

I have a 1998 Sea Ray Express Cruiser 215 with the original Merc 5.0 TBI. The boat starts and runs great below 3/4 throttle. The if increase to wide open throttle, the engine hesitates and won't go any faster and the RPMs drop to like 2,000. It also sounds like it is backfiring. I have heard it might be a faulty anti-siphon value but I replaced it and it still has the problem. I checked the compression in the engine and it seems fine. I changed the fuel filter and out new gas in. Nothing. Any ideas?

 

[Bt Doctur]

the fuel pump pressure or clogged injectors

 

[DollarBoat]

What's the best way to check for and fix clogged injectors?

 

[harleyman1975]

At this point it is trial and error. pull them and get them cleaned professionally...about $25 a pop.

 

[HT32BSX115]

I changed the fuel filter and out new gas in. Nothing. Any ideas?

Howdy,


Welcome aboard!

I think you may still have fuel delivery problem. You might try a "flow" check to see if you have enough fuel flow to the throttle body.

You also have a fuel pick-up screen in the tank before the anti-siphon check valve and a fuel tank vent. 1 or both may be partially clogged.


With the fuel pumping the fuel into a container, remove the fuel cap from the tank and see if there's suction on the tank (vent plugged)

If you have adequate flow to the TBI, It may be plugged at the TBI.


Cheers,

Rick

 

[alldodge]

What's the best way to check for and fix clogged injectors?

IMO suggest checking fuel pressure first, should be 30 psi at 1800 rpm using a fitting placed in line with the TBI, part number 91-806901

 

[DollarBoat]

Can I use any fuel pressure gauge with this? Like this one http://www.amazon.com/gp/aw/d/B004K...-2358-593e-99ee-92c15149bb20&pf_rd_i=15707421

 

[Fun Times]

Can I use any fuel pressure gauge with this? Like this one http://www.amazon.com/gp/aw/d/B004K...-2358-593e-99ee-92c15149bb20&pf_rd_i=15707421

No that kit is for testing engine/cylinder compression and it won't connect to the Mercruiser fitting part number 91-806901 like shown in post 6 above nor would that gauge read correctly.

You'll need to try and get a gauge similar to these ones http://www.autozone.com/test-scan-and-specialty-tools/fuel-pressure-tester or http://www.harborfreight.com/fuel-injection-pump-tester-92699.html

But before you do buy a gauge, you'll need to ensure the connecter of the gauge will screw onto the long thin fuel schrader valve adapter. If not, http://www.hardin-marine.com/c-1967-efi.aspx

 

[Bulabula78]

Do you have a cross redference part number from autozone or anywhere?

IMO suggest checking fuel pressure first, should be 30 psi at 1800 rpm using a fitting placed in line with the TBI, part number 91-806901

 

[alldodge]

The fittings are different then the standard GM TBI, you will need the Merc fitting. The standard GM uses an O-ring seal and not the flare fitting as Merc uses.