1995 Mercury 2.5l 175hp carb ignition issues

[Rider_560]

I have a freshly stock rebuilt Mercury 2.5l 175hp carb model. All cylinders bored .030 over with 125-130 psi except cylinder 2, which is registering 122/123... Timing was set at 22* without idle box and 19* with idle box. Ran better with the box, but I believe it was using the advance and retard function of the box to mask the ignition system dropping a cylinder. Box was only installed on most recent trip.

Motor has been run and I have been suspicious that it seemed under powered. It is on a 26ft deck boat and the boat has been toping out at 30/31 mph and only around 4800/4900 rpm. Would only achieve more rpm when trimmed up (and trimmed to far I believe).

Motor had 2 new switch boxes installed when I rebuilt it. The boxes were advertised as CDI, but later found out they were branded JAE.

Last night (in the dark) I put a timing light on each cylinder to see how the light reacted while rpm increased (dropping a cylinder or cutting out). As soon as I started, cylinder 1 and 3 we're not firing at all (which is weird because I adjusted timing and rechecked several times on cylinder 1). Cylinder 5 was intermittent, only firing about half the time, but when it did fire, it was normal, not intermittent. I could get cylinder 1 and 3 to fire intermittent when revving high rpm. Note: when revving timing did not advance as i just push the lever on the carb butterflies. I switched out the switch box to a good one and only cylinder 1 wouldn't fire. Then I went back to the original 2 switch boxes and switched the stator wires to the switch boxes (red, red/white, blue, blue/white). The problem did not follow the stator. Then I switched those wires back and swapped the switch boxes around completely. Problem followed the box. I feel as though I have a bad "new" switch box but also believe I may have a stator problem. I know stators can kill switch boxes and vice versa.

I have a dva adapter on the way (should be here Friday). I believe I have a bad switch box, but also believe my stator to be faulty. I'm considering replacing the trigger, switch boxes, and stator. Would you guys replace all those at the same time? Trigger seems to be functional. Should rectifiers be replaced with stators? I know they (or lack there of) can fry electrical components.

Any input would be helpful and greatly appreciated!! Thanks in advance

[Fishinmymission]

From what you said I'd start use the working switch box and the switch box that only cylinder one doesnt fire. Swap them and see if the issue follows the switch box. If it follows the switchbox you need another one. If it doesnt follow the switch box check the trigger wire is signaling to cylinder one, check cylinder 1 ignition coil, perform dva checks from stator.

If you're still perplexed I have a full set of 1995 175 carbureted electronics. I can guarantee the whole set of electronics work as the engine died from a main bearing failure due to being over propped. The stator, trigger switchboxes and volt regs are all one year old and ran fine for the last year of the engines life in 2017.
https://www.screamandfly.com/showthread.php?330872-Seized-175-HP-1995-Power-Head-I-m-taking-it-apart-but-would-like-to-know-my-options/page3
Being over propped was my reason for low rpm, wasted power being outside of the power band. Its about a 4500 lb (loaded) 23 ft cuddy cabin fishing boat went only 33 mph on a 19 pitch prop but gained 350 rpm and went 39 mph on a 17 pitch prop.
Let me know if your interested in certain parts and I'll just looks up the lowest ebay prices and undercut 10%.
You should be able to solve this problem though.

[Rider_560]

I will probably take you up on that. All of the parts were only 1 year old? Please let me know a price. Is that trigger, switch boxes, rectifiers, and stator?

[Rider_560]

With it being a newly rebuilt motor, I wouldn't mind everything being new!

[Fishinmymission]

I'd have no problem selling you a working set but you might be on the verge of solving it. I had these momentary bearing roller seizure which would give instant dips in rpm, i thought it had to be something electrical that i didn't understand. I replaced everything with new parts in 2017 except the ignition coils. Didn't change anything and I felt like an idiot. I even dissected an expensive older stator going crazy that was perfectly fine. The day it finally seized the roller seizure got very frequent about an hour before the bearing race disintegrated and crank jammed. I'm certain the electronics are fine.
Here are the dates i bought the items and what I think is a fair price. Let me know if you can find for cheaper. Ill cover shipping.
6/4/2017 2 CDI switchboxes $65
6/13/2017 CDI Stator $275
8/22/16 2 rectifiers(voltage regulators) $65
6/15/17 CDI Trigger, $100
Everything else in the picture except for the trim relays Free. Probably original to the engine starter relay, plates, ignition coils, plug boots. I don't wan to spend the time disassembling.
417984

[Rider_560]

Okay. The $500 is a little out of range at the moment. I'd definitely like all new electronics, I will keep it in mind. The powerhead was expensive enough! Lol. I will test my dva adapter when it comes Friday.

[Rider_560]

I also remember the last two times out I noticed the volt meter jumping to 16v, then back down to 13. Did this for a while until it stayed at 16v. I brushed it off originally as a defective guage. Now I am wondering if a rectifier or both could have been an initial cause of all of this. Could a rectifier cause these symptoms prior to destroying other components?

[Fishinmymission]

I reread your first message and it sounds like you have a second bad switchbox. I would try a third switchbox that you are positive works and if that one goes bad then look to the stator or flywheel which is much more labor intensive to replace.
Since you said the problem followed the box and you got cylinder 1 to fire when you switched the inboard and outboard boxes you know there is no issue with the trigger(as long as you didn't leave the wires attached to the boxes when you swapped everything else) or coil.
For the price of the rectifiers and the description you gave I would suggest replacing them as it is easy and cheap.
Might as well buy my two boxes so you have a spare incase another one blows, and buy the rectifiers. $120 for boxes and rectifiers Ill cover shipping.

[Rider_560]

I went to do more diagnosing this afternoon. As soon as I began to diagnose, it wouldn't start. Thru the timing light to each cylinder. Now I have no spark! I did have a maintenance free marine battery, not knowing that was a no no. Maybe that fried the stator? I sure wish we could work a deal on all of your electrical components!

[Merc 2.5]

I'm guessing a 40amp system? Is yours a water cooled regulator?

[Fishinmymission]

40 amp non water cooled is the design

[Merc 2.5]

If so I have stator for a water cold reg, and and reg 40 stator also , if it's what u need, I'll do 100 shipped if u need stator

[Merc 2.5]

418045

[Rider_560]

So the likely causes for no fire would be stator or both switch boxes? Would a maintenance free marine battery kill those?

[Merc 2.5]

I really wouldn't know about the batt , I've heard yes and no. Likely both switch boxes completely dead? I've never seen both dead completely, stator yes will kill all spark, prob rectifier to but again I haven't seen a rectifier kill all spark but I think I can?

[Fishinmymission]

Could be lots of things. If flywheel doesn't spin fast enough stator won't deliver enough power to charge the capacitor s in the boxes. Battery could not be spinning the starter and fly wheel fast enough, or it could be a bad stator or something made the stator go bad. Once you get your dva you should be able to see what the stator is putting out. Maybe the kill switch is open or closed I forget what it is. Aka make sure ignition switch is set to run and that wire is intact all the way back to the engine.

[Merc 2.5]

If you have no fire you should be able use multi meter w/o DVa to test stator , I tested my good stator without DVA and came within specs.

[Rider_560]

I'll double check the kill wire but the boat ran. Started getting intermittent spark to one switch box, swapped boxes, followed the box. Boat was still running during this. Then came back, next day, try to crank to do more diagnosing, no spark. Soulds like stator. Possibly both switch boxes, tho seems unlikely

[Rider_560]

Anyone?

[Fishinmymission]

Very unlikely both switch boxes. Look for something that effects both. Battery, stator, flywheel, trigger, kill wire.

[Rider_560]

Update;

Still waiting on dva, should be here tomorrow I hope.

I replaced both switch boxes with old units ( before rebuild) for testing, fired right up. First thing I did was use a timing light on each cylinder. All fine except cylinder 2 and 6. No fire at first. Moved throttle arm and began to rev engine. By 2k rpms both began firing. Both stayed firing. Ohmed stator, within spec. Ohmed trigger, within spec. Ohmed each coil wire from switch box, no resistance. Ohmed every ground wire I could find to engine block, no resistance. Check engine stop wire (black/yellow stripe) for voltage, zero with key off, 1v-1.2v with engine on. By this time engine has cooled. Time to check for spark strength. Set gap on spark tester to 7/16" gap. All jump the gap except 2 and 6. All plugs we're grounded while checking. Then I fired the engine up. Used timing light, no fire on 2 and 6, rev engine, fire comes back. Recheck spark gap, 2 and 6 then jump 7/16" gap. While running I tugged on trigger wires, didn't drop any cylinders. Pulled on switch box wire, no I'll effect. All of this was done with no bias circuit on switch boxes. The old switch boxes could be bad. But the rev has me thinking stator, possibly trigger. I'll be getting 2 new switch boxes regardless, I don't trust the old ones. I just don't want to ruin my new ones! Any help would be greatly appreciated. Thanks!!

[Merc 2.5]

2 and 6 on same box and yes I have a box n junk pile that missed on #6 until 1500ish rpm and would fire hot after that also. Get u 2 boxes preferably new but to test it try find 2 good ones and try it (ex the 1,3,5 box from that set and 1 box from another set that u know at least 1 is good,

[Fishinmymission]

Tricky set of symptoms you have but sounds like you are starting to really know the engine. The box that has no fire on 2 and 6 sounds like it is the box before that had no fire on 1 and 5. I would replace that switch box and that might be your only issue. Capacitors and electrical pathways can give intermittent problems that hard to diagnose as they change with thermals and vibrations. Sometimes i take apart or look with xray CT scans at electrolytic and ceramic capcitors at work when conducting failure analysis investigation on helicopter parts.
Are you running the other boxes that effect timing or are they removed?
Also check the stator as long is its always putting out in spec it wont hurt the boxes. The spec is written to only be read with a DVA to see what the stator is putting out. If you burn up another set of boxes look to the rectifiers, stator, and any timing boxes that are connected.

[Merc 2.5]

Always swap boxes in pairs or you will chase your tail sort a speak

[Rider_560]

I did replace both originally. They both went bad within a few hours. But the were also cheap eBay, probably China, switch boxes (assuming that's why the went bad). Going to replace both with quality brand. Probably CDI. Just wanna make sure I don't kill the new ones

[Fishinmymission]

They say to do in pairs as they worry about variations in spark power, profile, and timing between brands or production runs as it could theoretically effect timing or balance of the engine. Yeah tough choice as you might blow another more expensive set. I'll sell you my old stator, old boxes, and new rectifiers for $200. Older but it will probably solve your problem and I also gaurantee these are not defective.

Do you have any of the timing adjust boxes hooked up might want to start without them just in case. Running on retarded timing won't hurt anything while your diagnosing and you can always add back in. I forget if the engine has anything besides idle shifting.

[Merc 2.5]

If I had bet $ on it ,I'd say stator is fine and u bought (cheap) boxes that have been known to go out almost immediately,, theres quite a few members here that would sell you a set of known good boxes really cheap, may even send u a set to try and send back ,just so u know it would fix it b4 u buy new ones. Either way ,you have a switch box prob, I have tons rectifiers u can have for shipping cost and a good cheap stator if u want ,but if it were me I'd get 2 boxes and b dne

[Fishinmymission]

Merclovers a really nice guy. I'll send you my boxes at shipping cost just can't send till I go to my parents house which will probably be sometime this weekend. Fyi I owned that engine for 5 years. The first three my rectifiers never worked. Durring that time I had one switch box completely fail. I think it was like two or three years after I got the engine. So my experience is these are two components that ever failed me.

[Rider_560]

So what do you guys think about the 2 cylinders kicking in just over 1500 RPM or so in the old switch boxes. These were not a pair originally but I did not connect the bias and was only planning to use for testing. I would definitely appreciate the use of those old switch boxes. Could the switch box be kicking in on those 2 cylinders at slightly higher RPM due simply to higher voltage from the stator at higher RPM? Maybe, the contact may be burned enough to not allow voltage at low RPM. Though once the cylinders kick in, they remain active as long as the motor is running or warm, even at idle. When the motor cools, they won't work until motor is revved...

[Rider_560]

I missed a couple posts there. Sorry bout that. I see where the explanation for weak spark until higher RPM is covered. I'll switch the boxes around tonight and see if the weak spark follows the box.

[Rider_560]

I really appreciate the help so far! I'll keep you guys in the loop!

[Rider_560]

Fishinmymission, I'll take you up on those boxes if you get your hands on them.

Merclovers, I may take you up on the stator and rectifier if needed. I'm still waiting on the dva.

I appreciate the help

[Merc 2.5]

Try boxes 1st and go from there, unless it just test bad but I doubt it, I been through exact same thing and boxes fixed it, at the time I only changed 1 box and on the 2nd trip the other box went out, swapped to a pair and all was good. Good luck

[Rider_560]

Great. I'd imagine the china boxes could well be why I wasn't reaching full power or rpm originally as well?

[Merc 2.5]

Yes. I believe a few guys got them bad out of the package!! Good ignition parts is always $well spent imo

[Rider_560]

DVA came in today. I believe my multimeter is too cheap. Only one the auto parts store had. $20. Going to borrow one from work tomorrow an retest. My numbers were jumping around probably +/- 15v or so. All values were still in spec, Except my coil values were low.

But my dva numbers were also jumping around.

First question is... stator ohms out of spec but dva readings seem fine. If it passes dva, is it good? Or does it need to pass both.

Stator tests...

Test 1 then 2 ohm...
(Color to ground, CDI spec 5000-7000 ohms)

Blue to ground (1)4480 (2)6360

Blue/white to ground (1)4220 (2)4050

Red to ground (spec 90-160) test (1)123 (2)120

Red/white (spec 90-160) test (1)122 (2)119

Ohm test color to color (spec 3500-4200 ohms)

Red/white to blue/white (bouncing between) 5000-6000

Red to blue (bouncing between) 4000-4500

DVA readings @ 1000rpm test 1 then test 2...

Blue to ground (spec 195v-265v) test (1)230v (2)226v

Blue/white to ground (spec 195v-265v) test (1)210v (2)220v

Red to ground (spec 120v-160v) test (1)140v (2)150v

Red/white to ground (spec 120v-160v) test (1)140v (2)160v

DVA readings @ 3000rpm test 1 then test 2

Blue to ground (spec 255v-345v) test (1)300v (2)330v

Blue/white to ground (spec 255v-345v) test (1)310v (2)320v

Red to ground (spec 230v-320v) test (1)280v (2)295

Red/white to ground (spec 230v-320v) test (1)300v (2)300v

Trigger

Trigger ohmed within spec and all values were very similar. Also had approx. 40 volt while running between every lead and ground. Spec was 4+ volts

So what do you guys think. Stator is good and it is the switch boxes? I am ordering switch boxes tonight and I just don't want to ruin the new ones.

Thanks!

[Rider_560]

Re-did dva this evening with a fluke multimeter. First tests at 1k rpm. All measurements were in spec except stator dva test blue to ground. The volts on 2 coil were low, at first. Same 2 I was having firing issues with before. The volts on cylinder 1 and 5 (started as 2 and 6 then move switch box and firing problem moved with it) were low, around 1.5v, coil 3 was in the 200s (spec 125-175). The dva reading on the blue wire to ground was 295 (spec 195v-265v). Then I revved the engine a couple times (before spark was weak on 1 and 5, revved the engine, back to neutral. Spark then jumped 7/16" gap). Then re-did the dva readings on the coils 145v on all 6. Re-did dva reading on blue to ground, it was 210 (spec 195v-265v). I then checked all circuits at 3000rpm. All were within spec. I then rechecked values at 1000 rpm. All within spec.

I believe the short circuit in the bad switchbox is causing high voltage in the stator and low voltage to the coil. When revved and the short clears, voltage returns to normal at coils and stator. Would this be a plausible assumption? Is my stator likely bad? I have 2 switchboxes arriving tomorrow and don't want to ruin them. I don't mind buying a stator, I just don't think it's bad. I'm going to redo all DVA tests tommorow after the new switchboxes are installed. Would the testing procedure be enough time to ruin the boxes?

Thanks for any help in advance.

[Merc 2.5]

I understand ur concern 100% but I dont wanna say one way or the other but in past experiences when I had a bad box it didntnhurt stator or Visa versa , i would put new boxes on and check fire before you start the engine, sounds like if it sits it wont fire but will when warm,,so theoretically if it fires with new boxes cold,you should be safe to run , if acts same gonna b stator. I'm pretty positive you got the fix on the way, install,test,run, if you fry boxes by testing then I'd have to say you hooked something up wrong

[Rider_560]

Need some help please!! First time using DVA. DVA is attached to fluke multimeter.

I redid readings today immediately after installing new CDI electronics switchboxes. Revved motor to 1k rpm. I'm going off of my tach, not sure how accurate it is. Volts on red and red/white stator leads were low, 95-100v on red and 110v on red/white. Spec is 120v-160v. Blues were in spec. I cut the boat off. Literally for Less than 1 minute. To walk to the truck (attached to the boat) to grab a pen and write down readings. I cranked the boat back up. Never revved it or anything. Slowly revved back to 1k rpm. Specs were then 135v on red, 130v on red/white (spec 120v-160v). Blue checked 205v, blue/white 195v (spec 195v-265v).

I then revved to 3k rpm, to check those specs. 268v on blue, 275v on blue/white (spec 255v-345v). 270v on red, 268v on red/white (spec 230v-320v). I was going to cool and recheck but ran out of gas.

My stator may be bad but I'm not 100% convinced. I had 138v-145v at all 6 coils the whole time. Spec is 125v-175v. What do you guys think, is my stator good to run?

[Rider_560]

Again, I'm not sure how accurate rpm tach on dash is. All were in spec on second start up. Motor was no warmer or cooler for second startup.

[Merc 2.5]

Do you have a extra stator to try?

[Rider_560]

I dont

[Rider_560]

I was going to recheck tomorrow when I get more gas. Based on that, would you consider my stator bad?

[Merc 2.5]

Can u send me a pic of yours?

[Merc 2.5]

Based on ur readings it was out of spec but let me ask. Did boxes fix firing issue?

[Rider_560]

I can tomorrow, the camera on my phone doesn't work. I can use my wife's tomorrow. It looks like this...418670418670

[Rider_560]

Yes. As soon as I fired the motor I checked volts at both all coils, all were 138v-145v.

[Merc 2.5]

418671

Should be this one??

[Rider_560]

Yeah, it's that one.

[Merc 2.5]

If this is like yours. U pay shipping and I'll send it to u to try and if u wanna buy u can

[Merc 2.5]

If not send it back

[Rider_560]

That would be great! I want to double check specs tomorrow. How do we go about setting that up?

[Merc 2.5]

PM sent for contact info

[Rider_560]

Is the CDI trouble shooting guide based on cranking speed? There spec is 25v-100v red and 180v-400v blue

[Rider_560]

Talked with a CDI electronics tech support guy this morning. He claims my numbers are within spec, even the initial low reading, per their books. I will retest this evening and let everyone know if anything changes.

[Merc 2.5]

Go run that thing and c what it does!

[Rider_560]

Yessir! Gonna double check specs this evening and head to the lake tomorrow evening! I thought it was weird that Mercury and CDI had different specs. Their specs are for cranking speed but the red wires are 25v-100v and 180v-400v at cranking speed. He said I was good at 1k rpm

[Merc 2.5]

Sounds like u have done plenty testing and research, which is good learning,but I think u need give it a shot. Hs it been firing like suppose to during testing?

[Rider_560]

Yeah, ever since I put new switchboxes on it, I've had 138v-145v on every coil. Spec is 125-175. The 2 bad cylinders we're previously <1v. Plus firing via test light. I haven't put the spark gap tester back on them yet, but I think I'm good

[Rider_560]

DVA readings were in spec last night. According to Mercury and CDI spec. Lake this evening to see what she'll do

[Merc 2.5]

Does it run?

[Rider_560]

It seemed to run well. Finally got my rpms up. About 5600 rpms and 37-38 mph. Not too bad for a 26ft deck boat. It started surging for 10-15 minutes. 300-400 rpm increase/decrease. Did it at almost any rpm range. 99% sure my tank just needs a good cleaning. There was mess all in my fuel filter. I can see stuff at the bottom of the tank. Sometimes when I prime the fuel bulb, you can hear it having a hard time sucking fuel and takes 15-20 squeezes before it starts to take. Sometimes it only takes 4 or 5. Cleaning the tank today! Only other thing it could be besides the tank is a coil dropping in and out. My stator checked good, with Mercury specs, every time after the first time. Trigger good. Carbs clean. Fuel pump rebuilt. Timing correct, 23* WOT. No black boxes. I'm pretty confident its the tank. On the way back it ran perfect, no surging, 5600 rpm each time I tried. I appreciate all of your help!!

[Merc 2.5]

Thanks for the update. Sounds like you have bout got her dialed in. Good luck