I suspect these are related symptoms. Car has no problem turning over but has a hard time actually starting when cold. I can hear the fuel pump prime when I turn the key ON. Once it starts, I can shut it off and it will immediately restart without issue.

Additionally, hot or cold, the car bogs down with no power under WOT. Part throttle feels fine. I've done most of the standard tune up items (plugs, cap, rotor, timing belt, fuel filter). No check engine light (and the bulb test works).

Here's what i'm working with now:

1 - with no CEL, could it still be a TPS or coolant temp sensor problem?
2 - Could this be the symptom of an incorrect timing belt installation?
3 - Clogged cat? Low fuel pressure?
4 - Main relay going bad?

I've gone through the Honda service manual troubleshooting flowcharts and they all pretty much show a CEL, which I do not have. Right now I suspect its a fuel problem since it will restart fine after it starts for the first time.

Any help is appreciated! Thanks! It's a 92 EX 5-speed.

 

Yeop, you will have to do diagnostics to verify.

TPS does not always set a code, in fact it tends to NOT set a code when faulty.
Verify ECT sensor is measuring actual coolant temp. If it is stuck the ECM will not recognize it as bad but will cause the car to run out of tune.

If the timing belt was just changed and this is now happening then most likely.
Always verify that the timing is correct by placing crank at TDC and verifying the cam sprocket is either facing up with the UP arrow or facing down with the UP arrow. And that there is no slop in the belt. If someone loosened the tesnioneer pulley nut then the belts would be sloppy.

Clogged cat wouldn't really cause a hard starting issue, if it did the engine would barely run.
Low or incorrect fuel pressure would. If the FPR is failing or the pump is not putting out enough pressure due to motor or filter problems then there could be hard starting/running issues.

If the main relays contacts are worn, yes.
Verify the fuel pump is getting battery voltage. If not check to see where the problem lies.

 

Thanks for the suggestions Mike.

Very useful to know that a CEL is not a guarantee. I have a spare throttle body and TPS I can use to diagnose my current one.

The problem was there before I installed the timing belt.

Hopefully between the TPS, coolant temp sensor, and fuel pressure I can figure out what needs to be done next. I mistakenly replaced the temp sender, not realizing that it only controls the dashboard gauge. Haven't tested the ECM sensor. Newbie mistake.

 

Another possibility are clogged EGR ports. The procedure to clean them is referenced in one of the stickies. The new port covers cost about $4 at the dealer. You will need a drill, drill bit, slide hammer, carb cleaner, a small wire brush, and a non-metallic scraper. There are youtube videos as well. I have done it, and it is not that hard at all.

 

I checked fuel pressure today. With key ON and engine off, pressure would not go above 20 psi. Obviously below spec of 30-38 psi (per Honda FSM).

I'll try swapping the fuel pressure regulator first since i have a spare. Any other way to diagnose if the fuel pump is bad? Do they "get weak" like this? I figured they would just die altogether. Would rather not drop the tank unless I really have no choice.

 

You may try to artificially raise the PSI by (gently) pinching off the return fuel hose after the FPR. If the pressure can be raised then it is possibly the FPR, but with the pressure that low I would suspect either blockage(filter or tank sock) or pump issue(dying or not receiving battery voltage).

 

Tried swapping fuel pressure regulators with a known good one. Same result. Here is the pressure reading with key ON, engine OFF:



Here is with key ON, engine ON:



First reading is definitely below spec. Second reading is barely within spec. Maybe low voltage to the pump? Next thing to test.

EDIT: Just saw your response. Pinching the vacuum hose didn't change the pressure at all - I'm guessing the pressure is too low. Will check voltage at the trunk connector, then assuming it's OK, replace the pump.

 

Not vacuum hose, fuel return hose.

If there is a blockage/restriction between the pump and fuel rail, but the pump is fine, the fuel pressure may be able to rise up and equalize across the restriction if you create a larger restriction or block flow.

If the pressure does rise then the pump may be fine and there is a restriction between the pump and the fuel rail. I would then look at the fuel filter. Which would be a good component to replace anyway if the pump has failed.

If the pressure does not rise then the pump is incapable of increasing pressure and the pump is dying the prefilter 'sock' has failed/clogged, or the pump is not receiving full battery voltage. Test voltage at pump connector, if it is good then pump removal to inspect.

 

Shouldn't the FPR block the return flow to the tank until pressure reaches 30-38 psi?

I tried applying battery voltage directly to the +YEL wire going to the pump at the trunk connector and still only got 20 psi at the rail.

 

Sorry I meant to reply to this earlier. Thanks for the tip. I actually did this procedure on the car that I just wrecked, haven't gotten around to it on this one yet.

 

Just an update. No matter what I did, I couldn't get pressure to go above 20 psi with the engine off. It would go up a little bit (~26 psi) when the engine running, probably because of the higher voltage from the alternator. I even tried applying direct +12v from the battery straight to the connector in trunk.

Swapped in a known good pump + fuel tank and all is well, car runs like a top, starts easily, and fuel pressure is about 38 psi while running. Thanks everyone for the help.

 

Run the car for a bit. Then turn off the engine and remove the fpr vacuum hose from the intake manifold and smell it. Obviously it shouldnt smell like fuel. If it does, the fpr is bad.