won't rev over 3600 (fuel injector issue?) 7.4l

1

1990dtgl98

Member
Sep 21, 2020
37
Boat Info
1999 bowrider
Engines
Mercruiser
So here's the deal.

I bought a project 1999 searay 230br. Mercruiser 7.4L L29 engine. Got it running decent after a bit of back and forth. I still have an issue with it not revving over 3600 rpm under load.

I replaced cap/rotor/coil/plugs and wires last season. Set base timing with a techmate.

Had to replace the fuel pump as I only had 20psi.

Now I have spark and good pressure at the rail.

However it still won't rev over 3600, and the hole shot pulling skiers/wakeboarders up still feels subpar.

So this weekend I did a spark test, pulling wires and seeing if it sounds different under load. #5 and #6 had no perceptible change.

I pulled some plugs before having to put the kids to bed and here's how they look.

Looks like #5 is dead. Could it just be an injector? I had so much with the cool fuel and am hoping it could just be dead? Do they just quit like that? Doesn't smell gassy or look wet, like it was a clogged and spraying bad.

Buy a set of 8 injectors and be done with it?
 
Last edited:
Before spending any money on expensive parts, lets eliminate some more cheap/easy items. That boat should jump up and fly!

What outdrive Bravo 1 or Bravo 3?

1. How are you measuring RPM? The dash tach is notoriously inaccurate, you need to get a photo tach on it.

2. Re-check that you have set the timing right and that the wires are on the correct plug/cylinder. I've mixed them up and similar result to yours.

3. Fuel Filters - If they haven't been changed, change them. If none installed, might want to add one.

4. What prop is on the boat? Here is what Sea Ray shipped it with. A PO might have thrown something too aggressive on, limiting your RPM.

upload_2022-6-16_7-27-16.png
 
1990dtgl98 said:
So here's the deal.

I bought a project 1999 searay 230br. Mercruiser 7.4L L29 engine. Got it running decent after a bit of back and forth. I still have an issue with it not revving over 3600 rpm under load.

I replaced cap/rotor/coil/plugs and wires last season. Set base timing with a techmate.

Had to replace the fuel pump as I only had 20psi.

Now I have spark and good pressure at the rail.

However it still won't rev over 3600, and the hole shot pulling skiers/wakeboarders up still feels subpar.

So this weekend I did a spark test, pulling wires and seeing if it sounds different under load. #5 and #6 had no perceptible change.

I pulled some plugs before having to put the kids to bed and here's how they look.

Looks like #5 is dead. Could it just be an injector? I had so much with the cool fuel and am hoping it could just be dead? Do they just quit like that? Doesn't smell gassy or look wet, like it was a clogged and spraying bad.

Buy a set of 8 injectors and be done with it?
Click to expand...
A compression check should also be on the list.
 
dtfeld said:
Before spending any money on expensive parts, lets eliminate some more cheap/easy items. That boat should jump up and fly!

What outdrive Bravo 1 or Bravo 3?

1. How are you measuring RPM? The dash tach is notoriously inaccurate, you need to get a photo tach on it.

2. Re-check that you have set the timing right and that the wires are on the correct plug/cylinder. I've mixed them up and similar result to yours.

3. Fuel Filters - If they haven't been changed, change them. If none installed, might want to add one.

4. What prop is on the boat? Here is what Sea Ray shipped it with. A PO might have thrown something too aggressive on, limiting your RPM.

View attachment 128840
Click to expand...

Bravo 3

rpm measured with a techmate.

Timing set with techmate pro...wires are double checked, in correct order.

Fuel filter changed last summer, has about 15 hours on it.

Checked the prop..has the factory pitch/part number as what it came with from the factory.
 
While compression could be an issue, the fact you had Cool Fuel issues certainly points at fuel delivery. Could be clogged injectors, but also check the electrical side too. Corrosion is a known issue. Are you now or has the boat been in salt water?
 
dtfeld said:
While compression could be an issue, the fact you had Cool Fuel issues certainly points at fuel delivery. Could be clogged injectors, but also check the electrical side too. Corrosion is a known issue. Are you now or has the boat been in salt water?
Click to expand...

Boat has definitely seen time in saltwater. Engine bay looks pretty good but there are signs of corrosion back side of the block, as well as the anodes being corroded on the outdrive.

As far as how long and to what extent....I have no idea.

Since I need to pull the plenum off, I might buy injectors from somewhere I can return them, then start testing the connections to see if I even have juice at each injector.
 
Just pull the injectors and have them ultrasonic cleaned/tested by a reputable shop. Way cheaper
 
No-one is going to refund used injectors and the cheap chinese stuff just doesn't work. Good ones are big bucks, send yours out for service.
 
scoflaw said:
No-one is going to refund used injectors and the cheap chinese stuff just doesn't work. Good ones are big bucks, send yours out for service.
Click to expand...

Or buy a new set of reputable injectors, swap em out and send the old ones to be refurbished. Now have a spare set.
Check Summit Racing and Jegs for injectors.
 
You could test that injector by checking to see if it has continuity, applying 12V to it with jumpers and seeing if it "clicks", or by swapping it with another injector to see if the problem moves to the other cylinder. If you do remove it, then check that little screen on the input side to see if there's any debris in it. If there is, then there's probably debris in the rest of them too. You can get new screens or carefully pull the old ones out and clean them.

When you were checking/setting the timing, did you also verify that it was also advancing properly with RPM increases?
 
Bill Curtis said:
Or buy a new set of reputable injectors, swap em out and send the old ones to be refurbished. Now have a spare set.
Check Summit Racing and Jegs for injectors.
Click to expand...

Not sure if you would know a crossover but the mercury part number doesn't coincide with any gm numbers.

If I look up a generic 1999 3500 gm 454 I can find injectors, I just don't know if they are interchangeable.

802632t is mercruiser. 19244615 looks to be the late 90s 7.4 in a Chevy pickup.

I also noticed these reman ones on ebay. Seems like theyre cleaned, flow tested and oem, with positive reviews. Might be my best option? (Not sure if links are allowed):

https://www.ebay.com/itm/1918092097...624&ssuid=&var=&widget_ver=artemis&media=COPY
 
Not the same, merc injectors are short. Not only are they back ordered but there about 200 each.
Boats Unlimited has high quality ones for less than half that price. 817-658-772

I wouldn't give up on your yet, send them out for testing and cleaning.

Another thing about the chinese knock offs is you can't tell the difference externally.but you can if you flow test them.
 
Try to do a play by play update.

Pulled all plugs and checked spark at the plug. All looked good.

Looks like #5 and #6 have no combusion.
 

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Compression test:

1- 160
2- 160
3- 150
4- 155
5- 158
6- 161
7- 151
8- 160
 
2 of the 3 items necessary are present I.e. air/compression and spark, so obviously there is a fuel problem. Any shops nearby that test and clean injectors?
 
Called around some performance shops and the closest is about an hour and a half, 22 per injector (includes new screens and o-rings) and is on a 7-10 day turn around.

Might go with that reman oem ebay set for 150 more and have them in 3 days. Seller has perfect reviews.
 
Injectors all ohm'd between 12.3 and 12.5

Power and pulse to all wire.

Pulled the rail and got 1 bank off so far. Injectors are all heavily clogged. Rail doesn't have any pieces in it.

Do I need to worry about the new injectors clogging or do you think the rust was a combo from sitting for so long and the fuel pump being bad (which I replaced).
 

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Is there a secondary high-pressure filter before the injectors? If so, you might want to change that before you reinstall the injectors.
 
There's only a fuel pressure regulator. I have a new one to install.
 
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