Ok I just rebuilt the engine in a 99 solara. I bought the car with 200,000+ and a blown engine and I dont have any history on it. I pulled it and done a complete rebuild top to bottom. During the first warm up and initial break in it seemed to run ok (no hesitations/stalls/skips) so I changed the oil and went out to do some pulls. After a couple of 3/4 throttle pulls in 2nd gear in started hesitating/stalling/skipping or whatever you wanna call it. I mostly does it under load around 3k rps. the car looses power, rpms drop, engine light illuminates every time it does it. it does it randomly but rapidly, causing the car to start bucking. if i let off the gas it will smooth out.

There is no pending or stored codes so far according to my scanner

It has new wires and platnum plugs

none of the sensors are new and i don know their age

I bought a new coil and swapped it out with both of the old ones without any change. I took the new one back to the store

looking for more ideas. but I don't wanna just keep throwing $60-100+ sensors at it.

 

V6 or 4 cylinder engine?

Was the engine running when you purchased the car and if so did it operate OK?

Keep the scanner connected when doing pulls and determine if codes show up with the check light. If the scanner has real time data output of fuel trim, etc, check this.

The fuel system itself (pressure, flow, etc) is not monitored by the computer but fuel trim is. A too lean or rich mixture will set a code. This may reset once the trim changes.

Rather then change out parts test them. You must have some manual for rebuilding. Testing can be done for most sensors using an ohm or volt meter.

Check the AutoZone websites vehicle repair guide section or a Haynes manual for test info.

Sensor age can effect performance such A/F-02 sensors but does not mean an old sensor is bad.

Suggest for now concentrating on getting OBDII codes or data when the check light is on, recheck all vacuum hoses, wire plug connections, sensor installations such as MAF or MAP sensor, TPS installation, etc.

How long did the car sit. Might be long shot but gasohol tends to break down quickly with time and water collects at the bottom of the fuel tank.

 

Its a 5sfe (4 cyl) The engine would start when i bought it somehow. It had no compression on 1 cyl. the ring lands on the piston broke. it was burning a ton of oil and had a ton of blowby. the previous owner kept driving the poor thing till all the oil was gone and then it spun all 4 bearing and kept running it lol. i had to buy new pistons/rods and turn crank . I was hoping for a ring and bearing job only. oh well.

I thought maybe I got the timing off during assembly so i checked and rechecked. tried advancing and retarding a tooth but never had any desirable results. I got it back the way I had it the first time now.

It is very possible that its just bad gas. I let it sit for 6 months or so. Im not sure how long it was sitting before I bought it. I put some seafoam in the tank and bought a new fuel filter. Im gonna replace filter after bad gas and seafoam are gone. It had about 1/2 tank now has about 1/4.

 

If the timing belt installation was off the engine would not idle OK.

The temp gauge needle should stay at a position slightly below the middle temp mark.

The engine could have had this problem when you purchased the car.

 

OK it isn't bad gas.

I tried to view the live data stream on my scanner but every time the engine hesitated the scanner would loose the signal from the ecu and give me an error telling me to check the connection. Everything was fine with the connection. I just turned off the scanner and then back on and all was good till the engine started stalling again.

Soooo I'm thinking it could be a bad ecu.

Anyone have any thoughts before I buy one?

 

Get the part number off the ECU and do an internet search. Ebay often has them. Make sure the replacement part number is the exact same as the old one.

First suggest checking wiring.

The data link has 4 wires.

The Brown wire is connected to the same brown wires in the engine compartment, all run to ground.

White/Black wire is ground.
Black wire goes to ODB fuse and cars 12V electrical system.
White goes to ECU.

Determine if the ground wires have a bad connection to ground. Make sure the Black 12V wire is receiving full voltage.

A drop in car voltage or bad grounds may cause the loss of single and engine problems.

 

I found an ecu on eBay. Got it shipped to my door for $50! Had to buy it. Maybe thats all it is..

 

(I tried to view the live data stream on my scanner but every time the engine hesitated the scanner would loose the signal from the ecu and give me an error telling me to check the connection.)

scanner loose signal from ecm mmmmm ,ecm is turning off intermittent ,most people forget to do the simple thing when doing engine swaps, check for poor grounds from engine to body grounds .

to set the correct timing on a 5sfe engine can be challenging , first of the cam timing is the dots behind the cam gears there is a very important step when installing cams on to the head if you notice one cam gear it's split this cam gear have a spring in it pre. tension is require on this cam gear to prevent noise from cams and premature ware , then the timing belt time of course TPD on the crank and the cam cap have a notch ,the notch is the correct timing beside that is a dot mark DO NOT USED DOT MARK FOR TIMING DOT MARK IS FOR INSTALLATION OF THE HEAD TO BLOCK ONLY to prevent valve damage when installing it back together.

 

update:

I put in a new to me ecu, checked and rechecked all the grounds, they all look good

problem is still there.

Im not understanding this at all.

Anyone got any other suggestions of where to go from here?