Bogs down when accelerating

Welcome to 2CarPros.

You indicated that you replaced the timing belt and several vacuum hoses prior to this happening. Did you recheck your work? Also, have you checked for a plugged catalytic converter? I do need clarification on one thing. Does it seem the transmission is slipping?

Now, you said it has 55 psi fuel pressure. That is actually too high. I'm questioning if it is running too rich, which could in turn damage the catalytic converter. Here are two links. One discusses symptoms of a bad converter and the second one explains how to check.

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Here are the manufacturer's specs as far as fuel pressure.

At Idle, vacuum to regulator .................... 190 - 200 kPa (25 - 30 psi)
At Idle, NO vacuum to regulator .................... 280 - 320 kPa ( 41 - 46 psi)

Also, if you remove the vacuum hose from the fuel pressure regulator, is there any evidence of fuel in the hose?

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Let me know what you find with the converter and the fuel pressure regulator. Additionally, I strongly recommend checking for diagnostic trouble codes. This vehicle has an OBD1 system. If you follow this link, it explains how to retrieve codes.

https://www.2carpros.com/articles/odb1-isuzu-1985-1994-cars-and-trucks-code-retrieval-procedure-and-definition


Take care and I will watch for your reply.

Joe

On the converter issue i failed to mention i gutted it.. the increased horsepower is noticeable but it didn't change the problem. the rpm's will jump from around 2,600 to 3,500 no in between. That is when the bog down occurs.. it feels like it is starving for fuel at that point.. the transmission doesn't slip but it seems the bog down occurs at shift intervals..ie 1 to 2, 2 to 3 etc., but it is not only at those points. It is time the accelerator is depressed too much. at that point it may rev high but it sticks right here at whatever the rpm.is and will not accelerate. it feels like its running out of gas. lift your foot and depress the accelerator again and it will begin a slow acceleration but it does accelerate unless you give it more gas at which point the process repeats.. i was going to double check the timing marks this weekend though i am certain i got them spot on.. this is an interference engine timed to the number 2 cylinder at tdc and it works on a four cycle rotation to get the marks.aligned.. i would think even if i were a notch off by now the motor would be trashed and the belt i replaced though about to snap was.only 25% cut across its weak spot.. it didn't jump.timing my friend drove it.with the thing flapping until i finally told him it had to be done and did it for him. he.lets me use his other car and owns the house i live in so i am trying to help him out with this and i am failing miserably. i tested his coils found one bad. Verified by the number 2 plug not firing and him being electrocuted was all he needed to know to convince him to change the wires, lol.. his old plugs were gaped to .095, fuel filter reversed and so was the check valve for the emissions. i checked the EGR and that's good too, by the way. I will do as you suggest and check the pressure regulator tomorrow. thanks for the response I will let you know how it goes..

Here is some new information that just appeared out of the blue: .a misfire began last night very noticeable. he vehicle by the say at idle ran fine.. no bogging down whatsoever and accelerator pedal and fuel supply and spark were all in sync..

I used a spark tester and i can see the misfires i got three of them. cylinders 1-3 and 5. oddly this is the entire right hand bank of the V 6 and more oddly it represents only one tower on each coil and it is an intermittent miss coming from just those 3 cylinders.. 2-4 and 6 are working perfectly...

I don't know how the above scenario is even possible! New plugs new wires. I have to solve these misfires in order to go on. maybe i am just stuck on the coil packs and module being no good and the fact that i have to keep replacing them with used coils and modules isn't helping.. i guess i am looking to confirm my theory or offer an alternative because none of this makes any sense to me they should either work or not work. am i wrong?

Mote information. i changed the 2-5 coil thinking i could confirm the odd number cylinder misfire was not coil related.. it fixed the misfire in all 3 cylinders. i am thinking i have a wiring problem and the signal to fire those from the computer to the module is being broken or shorted along the way either from vibration or heat expansion.. i checked the vacuum line to the pressure regulator no fuel present. however, idle improved immediately when i disconnected the line and it started back up without issue.. I need to go out for ice so i am just going to stick a plug in the vacuum line and see if it helps or hurts. f it helps I will pick up a regulator while i am out and change it anyway.

I agree with you 100% on the misfire. There is a bad connection and moving things around is changing it I have attached two pics of the ignition schematic and circled things I need you to check. First, have you replaced the crankshaft position sensor? Next, confirm the connections circled are clean and tight. Third, make sure the ground on the engine is clean and tight. I have a feeling that is the problem. The ground is circled in both pics, but I added the second pic for you to see location.

As far as it running better with the fuel pressure regulator disconnected, that almost makes me believe there is a good vacuum leak and the added pressure is compensating. Also, you said it had 55 PSI fuel pressure. Is that with the regulator connected or disconnected?

Let me know,
Joe